Re: Passing hash ref [ was Re: finding head and tail in data structure
Hi Jim,
On Fri, Jan 11, 2013 at 1:54 PM, Jim Gibson jimsgib...@gmail.com wrote:
OR
print_path( $id, $routes-{$id} );
...
sub print_path
{
...
while( my ($start, $end) = each %$edges ) {
This is what i want, thank you!
Apparently passing $routes-{$id} is my earlier issue.
--budi
finding head and tail in data structure
Hi,
I have this following hash:
#!/usr/bin/perl
#
use strict;
use Data::Dumper;
my %MYROUTES = (
ROUTE-252 = {
# src = dest
427 = ABEP,
ABEP = 441,
441 = 427,
427 = 444,
444 = MGWQ,
MGWQ = CDEF
},
ROUTE-432 = {
AAA = BBB,
BBB = CCC,
CCC = DDD,
XXX = YYY,
YYY = ZZZ
}
);
print Dumper %MYROUTES;
__END__
Expected results:
ROUTE-252: 427 - ABEP - 441 - 427 - 444 - MGWQ - CDEF
ROUTE-432: Error: can not follow the route!
or if possible can be more specific on how many link founds:
Error, some path is missing:
ROUTE-432: AAA - BBB - CCC -DDD
ROUTE-432: XXX - YYY -ZZZ
I put data in order for brevity, actual data may not.
Can someone shed some light how to find head then follow the path as above?
Many thanks.
--budi
Re: finding head and tail in data structure
On Thu, 10 Jan 2013 17:01:43 +0700
budi perl budipe...@gmail.com wrote:
Hi,
I have this following hash:
#!/usr/bin/perl
#
use strict;
use Data::Dumper;
my %MYROUTES = (
ROUTE-252 = {
# src = dest
427 = ABEP,
ABEP = 441,
441 = 427,
427 = 444,
444 = MGWQ,
MGWQ = CDEF
},
You can't have the same hash key twice; you've duplicated 427 there.
Also, you don't need to quote the left side of a fat comma, so you can
just as easily say e.g. ABEP = 441.
Expected results:
ROUTE-252: 427 - ABEP - 441 - 427 - 444 - MGWQ - CDEF
ROUTE-432: Error: can not follow the route!
[...]
Can someone shed some light how to find head then follow the path
as above? Many thanks.
What have you tried so far? What have you got stuck on?
How do you know where the start of the route is? (Rememeber, hash keys
will come back in essentially random order; so, where do you start?)
If you need to start following from the first key you defined, you'll
need to either have an arrayref of hashrefs to iterate over, or store
the starting point as well as the routes.
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Re: finding head and tail in data structure
On Thu, Jan 10, 2013 at 5:19 PM, David Precious dav...@preshweb.co.ukwrote:
On Thu, 10 Jan 2013 17:01:43 +0700
budi perl budipe...@gmail.com wrote:
You can't have the same hash key twice; you've duplicated 427 there.
Also, you don't need to quote the left side of a fat comma, so you can
just as easily say e.g. ABEP = 441.
Expected results:
ROUTE-252: 427 - ABEP - 441 - 427 - 444 - MGWQ - CDEF
ROUTE-432: Error: can not follow the route!
[...]
Can someone shed some light how to find head then follow the path
as above? Many thanks.
What have you tried so far? What have you got stuck on?
How do you know where the start of the route is? (Rememeber, hash keys
will come back in essentially random order; so, where do you start?)
If you need to start following from the first key you defined, you'll
need to either have an arrayref of hashrefs to iterate over, or store
the starting point as well as the routes.
Here it is:
#!/usr/bin/perl
#
use strict;
use Data::Dumper;
my %MYROUTES = (
ROUTE-252 = {
# src = dest
CX77 = ABEP,
ABEP = 441,
441 = 427,
427 = 444,
444 = MGWQ,
MGWQ = CDEF
},
ROUTE-432 = {
AAA = BBB,
BBB = CCC,
CCC = DDD,
DDD = EEE,
EEE = FFF,
XXX = YYY,
YYY = ZZZ,
}
);
#print Dumper %MYROUTES;
foreach my $id (keys %MYROUTES) {
print $id \n;
# finding the starting point
my %found = ();
my $node = \%{$MYROUTES{$id}};
foreach my $src (keys %{$node}) {
print \t$src : ;
$found{$src} = 0;
foreach my $key (keys %{$node}) {
print $node-{$key} ;
$found{$src}++ if $src eq $node-{$key};
}
print \n;
}
# trace the path
my $sum = 0;
foreach(keys %found) {
print FOUND: $_ - $found{$_} ;
$sum += $found{$_};
}
print \n;
my $size = scalar keys %found;
print size: $size , sum: $sum\n;
if ($sum == ($size - 1)) {
print $id: has complete path\n;
} else {
my $total_route = $size - $sum;
print $id: has missing path, got $total_route different routes\n;
}
}
# should do recursively to print the route?
sub get_next {
my ($s, $n) = @_;
if ($n-{$s}) {
return 1;
} else {
return 0;
}
}
[budi@diavel bin]$ ./printroute.pl
ROUTE-252
427 : 444 441 ABEP CDEF MGWQ 427
ABEP : 444 441 ABEP CDEF MGWQ 427
CX77 : 444 441 ABEP CDEF MGWQ 427
MGWQ : 444 441 ABEP CDEF MGWQ 427
444 : 444 441 ABEP CDEF MGWQ 427
441 : 444 441 ABEP CDEF MGWQ 427
FOUND: CX77 - 0 FOUND: ABEP - 1 FOUND: 427 - 1 FOUND: 444 - 1 FOUND:
MGWQ - 1 FOUND: 441 - 1
size: 6 , sum: 5
ROUTE-252: has complete path
ROUTE-432
XXX : YYY DDD CCC FFF EEE ZZZ BBB
CCC : YYY DDD CCC FFF EEE ZZZ BBB
BBB : YYY DDD CCC FFF EEE ZZZ BBB
EEE : YYY DDD CCC FFF EEE ZZZ BBB
DDD : YYY DDD CCC FFF EEE ZZZ BBB
YYY : YYY DDD CCC FFF EEE ZZZ BBB
AAA : YYY DDD CCC FFF EEE ZZZ BBB
FOUND: XXX - 0 FOUND: BBB - 1 FOUND: CCC - 1 FOUND: DDD - 1 FOUND: EEE
- 1 FOUND: AAA - 0 FOUND: YYY - 1
size: 7 , sum: 5
ROUTE-432: has missing path, got 2 different routes
Looks ok to me, but ugly and need a way to print the full path.
Thanks!
--budi
Re: finding head and tail in data structure
On 10/01/2013 10:01, budi perl wrote:
Hi,
I have this following hash:
#!/usr/bin/perl
#
use strict;
use Data::Dumper;
my %MYROUTES = (
ROUTE-252 = {
# src = dest
427 = ABEP,
ABEP = 441,
441 = 427,
427 = 444,
444 = MGWQ,
MGWQ = CDEF
},
ROUTE-432 = {
AAA = BBB,
BBB = CCC,
CCC = DDD,
XXX = YYY,
YYY = ZZZ
}
);
print Dumper %MYROUTES;
__END__
Expected results:
ROUTE-252: 427 - ABEP - 441 - 427 - 444 - MGWQ - CDEF
ROUTE-432: Error: can not follow the route!
or if possible can be more specific on how many link founds:
Error, some path is missing:
ROUTE-432: AAA - BBB - CCC -DDD
ROUTE-432: XXX - YYY -ZZZ
I put data in order for brevity, actual data may not.
Can someone shed some light how to find head then follow the path as above?
This calls for a proper module that has been thoroughly tested. The
program below uses Graph::Directed. Beware that it does no checks for
things like cyclic links, but it does print the path to /all/ end points
starting at each source.
HTH,
Rob
use v5.10;
use warnings;
use Graph::Directed;
my %routes = (
ROUTE-252 = { 427 = 444, 441 = 427, 444 = MGWQ, ABEP = 441,
MGWQ = CDEF },
ROUTE-432 = { AAA = BBB, BBB = CCC, CCC = DDD, XXX =
YYY, YYY = ZZZ },
);
while (my ($label, $edges) = each %routes) {
my $graph = Graph::Directed-new;
while (my ($start, $end) = each %$edges) {
$graph-add_edge($start, $end);
}
my @sinks = $graph-sink_vertices;
for my $source ($graph-source_vertices) {
for my $sink (grep $graph-is_sink_vertex($_),
$graph-all_successors($source)) {
say $label: , join ' - ', $graph-path_vertices($source, $sink);
}
}
}
**output**
ROUTE-252: ABEP - 441 - 427 - 444 - MGWQ - CDEF
ROUTE-432: AAA - BBB - CCC - DDD
ROUTE-432: XXX - YYY - ZZZ
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Re: finding head and tail in data structure
Hi Rob,
This works and looks much more simpler. Thanks, i love it.
--budhi
On Fri, Jan 11, 2013 at 1:00 AM, Rob Dixon rob.di...@gmx.com wrote:
On 10/01/2013 10:01, budi perl wrote:
Hi,
I have this following hash:
#!/usr/bin/perl
#
use strict;
use Data::Dumper;
my %MYROUTES = (
ROUTE-252 = {
# src = dest
427 = ABEP,
ABEP = 441,
441 = 427,
427 = 444,
444 = MGWQ,
MGWQ = CDEF
},
ROUTE-432 = {
AAA = BBB,
BBB = CCC,
CCC = DDD,
XXX = YYY,
YYY = ZZZ
}
);
print Dumper %MYROUTES;
__END__
Expected results:
ROUTE-252: 427 - ABEP - 441 - 427 - 444 - MGWQ - CDEF
ROUTE-432: Error: can not follow the route!
or if possible can be more specific on how many link founds:
Error, some path is missing:
ROUTE-432: AAA - BBB - CCC -DDD
ROUTE-432: XXX - YYY -ZZZ
I put data in order for brevity, actual data may not.
Can someone shed some light how to find head then follow the path as
above?
This calls for a proper module that has been thoroughly tested. The
program below uses Graph::Directed. Beware that it does no checks for
things like cyclic links, but it does print the path to /all/ end points
starting at each source.
HTH,
Rob
use v5.10;
use warnings;
use Graph::Directed;
my %routes = (
ROUTE-252 = { 427 = 444, 441 = 427, 444 = MGWQ, ABEP = 441,
MGWQ = CDEF },
ROUTE-432 = { AAA = BBB, BBB = CCC, CCC = DDD, XXX = YYY,
YYY = ZZZ },
);
while (my ($label, $edges) = each %routes) {
my $graph = Graph::Directed-new;
while (my ($start, $end) = each %$edges) {
$graph-add_edge($start, $end);
}
my @sinks = $graph-sink_vertices;
for my $source ($graph-source_vertices) {
for my $sink (grep $graph-is_sink_vertex($_), $graph-all_successors($
**source)) {
say $label: , join ' - ', $graph-path_vertices($source, $sink);
}
}
}
**output**
ROUTE-252: ABEP - 441 - 427 - 444 - MGWQ - CDEF
ROUTE-432: AAA - BBB - CCC - DDD
ROUTE-432: XXX - YYY - ZZZ
Passing hash ref [ was Re: finding head and tail in data structure
Hi All,
I would like to pass hash: %{$routes{ROUTE-252}} instead of %routes but
got this error:
[budi@dev bin]$ ./print_path.pl
Type of arg 1 to each must be hash (not hash element) at
./print_path.plline 38, near })
Execution of ./print_path.pl aborted due to compilation errors.
#use strict;
use Graph::Directed;
use Data::Dumper;
my %routes = (
ROUTE-252 = {
# src = dest
CX77 = ABEP,
ABEP = 441,
441 = 427,
427 = 444,
444 = MGWQ,
MGWQ = CDEF
},
ROUTE-432 = {
AAA = BBB,
BBB = CCC,
CCC = DDD,
DDD = EEE,
EEE = FFF,
XXX = YYY,
YYY = ZZZ,
}
);
my $id = ROUTE-252;
print Dumper $routes{$id};
print_path($id, \%{$routes{$id}});
sub print_path {
my ($label, $edges) = @_;
my $graph = Graph::Directed-new;
while (my ($start, $end) = each $edges{$label}) {
#while (my ($start, $end) = each %{$routes{$label}}) {
$graph-add_edge($start, $end);
}
my @sinks = $graph-sink_vertices;
for my $source ($graph-source_vertices) {
for my $sink (grep $graph-is_sink_vertex($_),
$graph-all_successors($source)) {
print $label: , join ' - ', $graph-path_vertices($source,
$sink);
print \n;
}
}
}
Re: Passing hash ref [ was Re: finding head and tail in data structure
On Fri, 11 Jan 2013 10:33:02 +0700
budi pearl budipe...@gmail.com wrote:
my $id = ROUTE-252;
print Dumper $routes{$id};
print_path($id, \%{$routes{$id}});
I think you want:
print_path( $id, $routes{$id} );
--
Don't stop where the ink does.
Shawn
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Re: Passing hash ref [ was Re: finding head and tail in data structure
Hi Shawn,
When trying to accessed inside subroutine , i got:
Type of arg 1 to each must be hash (not hash element) at
./print_path.plline 41, near })
Execution of ./print_path.pl aborted due to compilation errors.
this is work:
while (my ($start, $end) = each %{$routes{$label}}) {
but this not:
while (my ($start, $end) = each %{$edges{$label}}) {
Thanks.
--budhi
On Fri, Jan 11, 2013 at 10:47 AM, Shawn H Corey shawnhco...@gmail.comwrote:
On Fri, 11 Jan 2013 10:33:02 +0700
budi pearl budipe...@gmail.com wrote:
my $id = ROUTE-252;
print Dumper $routes{$id};
print_path($id, \%{$routes{$id}});
I think you want:
print_path( $id, $routes{$id} );
--
Don't stop where the ink does.
Shawn
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Re: Passing hash ref [ was Re: finding head and tail in data structure
On Fri, Jan 11, 2013 at 11:05 AM, budi pearl budipe...@gmail.com wrote:
Hi Shawn,
When trying to accessed inside subroutine , i got:
Type of arg 1 to each must be hash (not hash element) at ./print_path.plline
41, near })
Execution of ./print_path.pl aborted due to compilation errors.
this is work:
while (my ($start, $end) = each %{$routes{$label}}) {
but this not:
while (my ($start, $end) = each %{$edges{$label}}) {
This will work, but this will pass %routes instead of %routes{$id}. Or it
should be that way?
my $hroute = \%routes;
print_path($id, $hroute);
...
while (my ($start, $end) = each %{$edges-{$label}}) {
Re: Passing hash ref [ was Re: finding head and tail in data structure
On Jan 10, 2013, at 7:33 PM, budi pearl wrote:
Hi All,
I would like to pass hash: %{$routes{ROUTE-252}} instead of %routes but
got this error:
[budi@dev bin]$ ./print_path.pl
Type of arg 1 to each must be hash (not hash element) at
./print_path.plline 38, near })
Execution of ./print_path.pl aborted due to compilation errors.
#use strict;
If you had not commented out this line, Perl would have told you what the
problem is.
use Graph::Directed;
use Data::Dumper;
my %routes = (
ROUTE-252 = {
# src = dest
CX77 = ABEP,
ABEP = 441,
441 = 427,
427 = 444,
444 = MGWQ,
MGWQ = CDEF
},
ROUTE-432 = {
AAA = BBB,
BBB = CCC,
CCC = DDD,
DDD = EEE,
EEE = FFF,
XXX = YYY,
YYY = ZZZ,
}
);
my $id = ROUTE-252;
print Dumper $routes{$id};
print_path($id, \%{$routes{$id}});
You are passing a reference to the inner hash, but you are doing it by first
de-referencing, then referencing the inner hash. This can be simply:
print_path( $id, $routes{$id} );
sub print_path {
my ($label, $edges) = @_;
You are storing the hash reference in the scalar variable $edges. This value is
$routes{'ROUTE-252'}.
my $graph = Graph::Directed-new;
while (my ($start, $end) = each $edges{$label}) {
There are two problems here:
1. $edges{$label} is a member of the hash %edges, but you have not declared or
defined %edges in your subroutine.
2. You are trying to access the member $route{'ROUTE-252'}-{'ROUTE-252'}. In
other words, you are indexing twice. You should either pass the top-level hash
and index in the subroutine, or pass the indexed hash member and do not index
in the subroutine:
print_path( $id, \%routes );
...
sub print_path
{
...
while( my ($start, $end) = each %{$edges-{$label}} ) {
OR
print_path( $id, $routes-{$id} );
...
sub print_path
{
...
while( my ($start, $end) = each %$edges ) {
#while (my ($start, $end) = each %{$routes{$label}}) {
$graph-add_edge($start, $end);
}
my @sinks = $graph-sink_vertices;
for my $source ($graph-source_vertices) {
for my $sink (grep $graph-is_sink_vertex($_),
$graph-all_successors($source)) {
print $label: , join ' - ', $graph-path_vertices($source,
$sink);
print \n;
}
}
}
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More on perl like tail
Sorry about being tricky with what was an older thread. But I suspect
that thread died... and no one noticed there was an unaswered question
still there.
Shawn C originally suggested I use File::Tail. There was a short
exchange about why and then I began trying to use File::Tail but
haven't been successful with it. The details are below:
Shawn H Corey shawnhco...@gmail.com writes:
open(FILE,./named-pipe) or die Can't Open ./named-pipe: $!;
while(FILE){
print;
if(eof){
sleep 2;
seek (FILE,0,1);
}
}
It seems at least to survive repeated restarts of system logger.
If I write my script based on this code... what I'd be adding would be
code to get 1 or 2 rgx from the cmdline, then write the hits to
various files.
[...]
In the general case, modules usually take care of special cases that you
may not be aware of. That makes them the preferred method of solving a
problem.
In this case, the above code is a kludge. You can tell this because the
program sleeps, rather than waiting on input. When a program does
something to emulate what it really should be doing, it introduces code
that may not work in all cases.
I'm having trouble with File::Tail... or more likely the way I'm
trying to use it is wrongly setup.
But first about that sleep comment. As I read a little of File::Tail
and its very likely I'm not really understanding what I'm reading but,
it appears to be saying that it `sleeps' at times... the times are
a little more sophisticated... but none the less sleep.
Now the problem.
I've taken the first examples in the perldoc File::Tail output:
(http://search.cpan.org/~mgrabnar/File-Tail-0.99.3/Tail.pm)
use File::Tail;
$file=File::Tail-new(/some/log/file);
while (defined($line=$file-read)) {
print $line;
}
And tied to make it work for my case (/var/adm/slpipe in the script is a
named-pipe that the system logger reads into):
cat fltr_sl
#!/usr/local/bin/perl
use strict;
use warnings;
use File::Tail;
my ($file,$line);
my $fname_in = /var/adm/slpipe;
$file=File::Tail-new($fname_in);
while (defined($line=$file-read)) {
print $line;
}
When I run it, it doesn't show any errors, and appears to be waiting
on the pipe.
But no data ever comes out. I used the same test sequence as for the
earlier script that didn't use File::Tail (posted earlier in this
thread). The sequence is.
1) start the script `fltr_sl' shown above
2) To make sure if data is flowing thru the pipe start
start (in a different xterm) tail -f slpipe too.
2) kill -HUP the system logger.
3) Ensure some data is flowing thru the named-pipe by
running ssh r...@localhost from a user account
I see 7-8 lines output to the tail -f slpipe command, but nothing to
the perl script fltr_sl.
And as I write this message, quite a few more lines are appearing at
the `tail -f slpipe' cmd, but still nothing at my perl filter.
Have I made some serious mistake in my attempted usage of File::Tail?
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Re: More on perl like tail
At 3:57 PM -0500 10/24/09, Harry Putnam wrote:
Sorry about being tricky with what was an older thread. But I suspect
that thread died... and no one noticed there was an unaswered question
still there.
Or no one knew the answer.
Shawn C originally suggested I use File::Tail. There was a short
exchange about why and then I began trying to use File::Tail but
haven't been successful with it. The details are below:
Shawn H Corey shawnhco...@gmail.com writes:
open(FILE,./named-pipe) or die Can't Open ./named-pipe: $!;
while(FILE){
print;
if(eof){
sleep 2;
seek (FILE,0,1);
}
}
I would modify the above a little. You are calling eof after each
line, which is unnecessary. The input operator FILE will return
undef whenever eof will return true, so calling eof is redundant. You
can make this a little more efficient with something like the
following (untested):
while(1) {
while(FILE) {
print;
}
sleep 1;
seek(FILE,0,1);
}
In this case, the above code is a kludge. You can tell this because the
program sleeps, rather than waiting on input. When a program does
something to emulate what it really should be doing, it introduces code
that may not work in all cases.
I'm having trouble with File::Tail... or more likely the way I'm
trying to use it is wrongly setup.
But first about that sleep comment. As I read a little of File::Tail
and its very likely I'm not really understanding what I'm reading but,
it appears to be saying that it `sleeps' at times... the times are
a little more sophisticated... but none the less sleep.
I do not agree with that kludge comment. When waiting for slow
events, you can either use polling or interrupts. Polling means
continually sleeping and then checking if the event has occurred. The
event in this case is additional data appearing at the end of the
file. Interrupt would mean blocking until the event has occurred.
That can be accomplished using the Unix select statement. In the
general case, interrupts are more efficient than polling, because
your process does not execute at all until the event occurs.
In this case, however, your process is waiting on another, slower
process: the file writer. If you were to use a select statement, at
the cost of increased complexity in your program, you would respond
faster to new data. However, sleeping for 1 second and trying to read
the file is not going to put a large load on your system. So the
simple method using sleep will cost you less than one second every
time you exhaust the file input in your reader process. If this is
acceptable, then using sleep is OK.
File::Tail does have a select method to improve response, but I think
that in most cases that is overkill. As you have pointed out, the
normal use of File::Tail involves calling the sleep function.
Now the problem.
I've taken the first examples in the perldoc File::Tail output:
(http://search.cpan.org/~mgrabnar/File-Tail-0.99.3/Tail.pm)
use File::Tail;
$file=File::Tail-new(/some/log/file);
while (defined($line=$file-read)) {
print $line;
}
That looks OK, and works for me on /var/log/system.log, although the
delays are longer using File::Tail than Unix tail. Maybe you should
try it on a normal file that you write to occasionally with another
Perl program.
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Re: More on perl like tail
Jim Gibson jimsgib...@gmail.com writes:
At 3:57 PM -0500 10/24/09, Harry Putnam wrote:
Sorry about being tricky with what was an older thread. But I suspect
that thread died... and no one noticed there was an unaswered question
still there.
Or no one knew the answer.
He he... unlikely here I think..
[...]
I would modify the above a little. You are calling eof after each
line, which is unnecessary. The input operator FILE will return
undef whenever eof will return true, so calling eof is redundant. You
can make this a little more efficient with something like the
following (untested):
while(1) {
while(FILE) {
print;
}
sleep 1;
seek(FILE,0,1);
}
That does look like it might be better... and thanks for the explanation.
[...]
use File::Tail;
$file=File::Tail-new(/some/log/file);
while (defined($line=$file-read)) {
print $line;
}
That looks OK, and works for me on /var/log/system.log, although the
delays are longer using File::Tail than Unix tail. Maybe you should
That isn't actually the version I used .. its a bit lower on the page
you cited above... but I can't see anything that make it work any
different.
cat fltr_sl
[...]
use File::Tail;
my ($file,$line);
my $fname_in = /var/adm/slpipe;
$file=File::Tail-new($fname_in);
while (defined($line=$file-read)) {
print $line;
}
try it on a normal file that you write to occasionally with another
Perl program.
One question, in your test you didn't actually run it against a
named-pipe did you? Would that be likely to make a difference?
Taking your suggestion I see the script above will ouput from a normal
file.
touch t1
./filterWithFileTail.pl (edited to open ./t1)
while [[ 1 ]];do
echo Now you've done it t1
sleep 1
cat ~/.bash_history t1
sleep 1
done
The File::Tail filter does eventually output the data coming in. You
mentioned it's slower.. it seems a good bit slower here.
But it will NOT ouput data from the named pipe.
I ran the same while loop writing to the named pipe and still the perl
filter with File::Tail won't output a thing.
Anyway I have a working script... soon to modify with your
suggestions. .. thanks for the help.
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Re: perl like tail -f
Shawn H Corey shawnhco...@gmail.com writes:
open(FILE,./named-pipe) or die Can't Open ./named-pipe: $!;
while(FILE){
print;
if(eof){
sleep 2;
seek (FILE,0,1);
}
}
It seems at least to survive repeated restarts of system logger.
If I write my script based on this code... what I'd be adding would be
code to get 1 or 2 rgx from the cmdline, then write the hits to
various files.
[...]
In the general case, modules usually take care of special cases that you
may not be aware of. That makes them the preferred method of solving a
problem.
In this case, the above code is a kludge. You can tell this because the
program sleeps, rather than waiting on input. When a program does
something to emulate what it really should be doing, it introduces code
that may not work in all cases.
I'm having trouble with File::Tail... or more likely the way I'm
trying to use it is wrongly setup.
But first about that sleep comment. As I read a little of File::Tail
and its very likely I'm not really understanding what I'm reading but,
it appears to be saying that it `sleeps' at times... the times are
a little more sophisticated... but none the less sleep.
Now the problem.
I've taken the first examples in the perldoc File::Tail output:
http://search.cpan.org/~mgrabnar/File-Tail-0.99.3/Tail.pm
use File::Tail;
$file=File::Tail-new(/some/log/file);
while (defined($line=$file-read)) {
print $line;
}
And tied to make it work for my case (/var/adm/slpipe in the script is a
named-pipe that the system logger reads into):
cat fltr_sl
#!/usr/local/bin/perl
use strict;
use warnings;
use File::Tail;
my ($file,$line);
my $fname_in = /var/adm/slpipe;
$file=File::Tail-new($fname_in);
while (defined($line=$file-read)) {
print $line;
}
When I run it, it doesn't show any errors, and appears to be waiting
on the pipe.
But no data ever comes out. I used the same sequence as for the
earlier script the didn't use File::Tail (posted earlier in this
thread). That is.
1) start the script `fltr_sl' shown above
2) To make sure if data is flowing thru the pipe start
tail -f slpipe too.
2) kill -HUP the system logger.
3) Ensure some data is flowing thru the named-pipe by
running ssh r...@localhost from a user account
I see 7-8 lines output to the tail -f slpipe command, but nothing to
the perl script fltr_sl.
And as I write quite a few more lines are appearing at the
`tail -f slpipe' cmd, but still nothing at my perl filter.
Have I made some serious mistake in my attempted usage of File::Tail?
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Re: perl like tail -f
Harry Putnam wrote:
Shawn H Corey shawnhco...@gmail.com writes:
http://search.cpan.org/~mgrabnar/File-Tail-0.99.3/Tail.pm
Thanks that looks useful. Is there a reason why I should use that
module as apposed to the kind of code offered in the faq about
tail? (perldoc -q tail) as suggested by another poster (Jim G).
I mean, I'm not experienced enough to know if there are things the
module handles that a simple script like the one below does not.
open(FILE,./named-pipe) or die Can't Open ./named-pipe: $!;
while(FILE){
print;
if(eof){
sleep 2;
seek (FILE,0,1);
}
}
It seems at least to survive repeated restarts of system logger.
If I write my script based on this code... what I'd be adding would be
code to get 1 or 2 rgx from the cmdline, then write the hits to
various files.
I'm told there is a systematic way to add my script to solaris bootup,
and to restart it automatically if need be. But other than those are
there other `gotchas' or whatever I'm liable to need the module for?
In the general case, modules usually take care of special cases that you
may not be aware of. That makes them the preferred method of solving a
problem.
In this case, the above code is a kludge. You can tell this because the
program sleeps, rather than waiting on input. When a program does
something to emulate what it really should be doing, it introduces code
that may not work in all cases.
--
Just my 0.0002 million dollars worth,
Shawn
Programming is as much about organization and communication
as it is about coding.
I like Perl; it's the only language where you can bless your
thingy.
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Re: perl like tail -f
On Mon, 19 Oct 2009 23:30:30 -0500, Harry Putnam wrote: Shawn H Corey shawnhco...@gmail.com writes: http://search.cpan.org/~mgrabnar/File-Tail-0.99.3/Tail.pm Thanks that looks useful. Is there a reason why I should use that module as apposed to the kind of code offered in the faq about tail? (perldoc -q tail) as suggested by another poster (Jim G). For code this brief, it's a toss-up. Using the module results in about the same amount of code; the advantage is that it's a bit more readable. In general, for tasks like this, you can expect a module to be more portable and featureful, and handle more special cases. You may never need any of its additional functionality, but if the day comes when, for instance, you want your code to be smarter about how fast it responds to changes in a file, the module would instantly become a better choice. -- Peter Scott http://www.perlmedic.com/ http://www.perldebugged.com/ http://www.informit.com/store/product.aspx?isbn=0137001274 -- To unsubscribe, e-mail: beginners-unsubscr...@perl.org For additional commands, e-mail: beginners-h...@perl.org http://learn.perl.org/
perl like tail -f
With a linux background I'm used to being able to my the system logger right to a named pipe buy means of a `|' (pipe) symbol in syslog.conf *.* |/var/log/fifo But on Opensolaris the system logger is enough different than the sysklogd daemon on linux that the `|' symbol is ignored in /etc/syslog.conf On opensolaris, you can tell syslogger to write direct to the fifo. But it has a side effect Lets say you create the fifo To get data flowing into your filter or script, syslog needs a restart. But first we use the easy example of cat. cat fifo Now restart system logger. Now anything that sys logger produces will be displayed from the cat command. Now restart systemlogger again and cat closes as would a common shell script or awk. However the `tail -f' command will not close... it keeps on reading through restarts. I want to get that behavior from a perl script. I realize I could have my script read from `tail -f fifo|script.pl' but that introduces another factor... a buffer filling factor where tail -f's shell buffer has to fill up between writes. That introduces a lag... so if you want a truly live syslog read.. you need some kind of fancy buffer flushing or the like. I'm not sure what it is about the tail -f command that allows it to keep reading over restarts of system logger (on Opensolaris)... but how can I emulate whatever it is.. in perl? -- To unsubscribe, e-mail: beginners-unsubscr...@perl.org For additional commands, e-mail: beginners-h...@perl.org http://learn.perl.org/
Re: perl like tail -f
Harry Putnam wrote: I'm not sure what it is about the tail -f command that allows it to keep reading over restarts of system logger (on Opensolaris)... but how can I emulate whatever it is.. in perl? Have you looked at File::Tail http://search.cpan.org/~mgrabnar/File-Tail-0.99.3/Tail.pm ? -- Just my 0.0002 million dollars worth, Shawn Programming is as much about organization and communication as it is about coding. I like Perl; it's the only language where you can bless your thingy. -- To unsubscribe, e-mail: beginners-unsubscr...@perl.org For additional commands, e-mail: beginners-h...@perl.org http://learn.perl.org/
Re: perl like tail -f
On 10/19/09 Mon Oct 19, 2009 11:38 AM, Harry Putnam rea...@newsguy.com scribbled: I'm not sure what it is about the tail -f command that allows it to keep reading over restarts of system logger (on Opensolaris)... but how can I emulate whatever it is.. in perl? There is an FAQ: perldoc -q tail See if that helps you. The idea is to read until the end-of-file is reached, pause for awhile, then try reading again. However, reaching EOF sets a flag in the file handle and subsequent reads will fail. The trick is to reset the EOF flag with a seek command, either seek($fh,0,1) or $curpos = tell($fh); seek($fh,$curpos,0); -- To unsubscribe, e-mail: beginners-unsubscr...@perl.org For additional commands, e-mail: beginners-h...@perl.org http://learn.perl.org/
Re: perl like tail -f
Jim Gibson jimsgib...@gmail.com writes:
On 10/19/09 Mon Oct 19, 2009 11:38 AM, Harry Putnam rea...@newsguy.com
scribbled:
I'm not sure what it is about the tail -f command that allows it to
keep reading over restarts of system logger (on Opensolaris)... but
how can I emulate whatever it is.. in perl?
There is an FAQ:
perldoc -q tail
See if that helps you.
The idea is to read until the end-of-file is reached, pause for awhile, then
try reading again. However, reaching EOF sets a flag in the file handle and
subsequent reads will fail. The trick is to reset the EOF flag with a seek
command, either
seek($fh,0,1)
or
$curpos = tell($fh);
seek($fh,$curpos,0);
It all sounds good so trying a simple example like the one below.
But being A bit unsure.. I can report that this simple example seems
to work... at least in so far as surviving repeated restarts of
system.logger. Am I making some non-obvious mistake here?
open(FILE,./named-pipe) or die Can't Open ./named-pipe: $!;
while(FILE){
print;
if(eof){
sleep 2;
seek (FILE,0,1);
}
}
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Re: display tail of monster file
叶孤城 gucheng...@freenet.de writes: 2009/9/27 叶孤城 gucheng...@freenet.de: 2009/9/27 Harry Putnam rea...@newsguy.com: Will it make any difference in loading time or cpu resource usage to use the `tail' command like 'qx/tail -n30 $file/' as apposed to something in straight perl like this example that prints the last 30 lines of $log: Not absolute that which is better. But `tail` will launch an external process that is generally slower. You may benchmark them to see the difference, using the module like: very sorry, copy a wrong link, the correct one: http://search.cpan.org/~dcoppit/Benchmark-Timer-0.7102/lib/Benchmark/Timer.pm Thanks for the link. After looking there... it appears the module concerns itself with timing. I wondered if timing will also tell you about system resource use. -- To unsubscribe, e-mail: beginners-unsubscr...@perl.org For additional commands, e-mail: beginners-h...@perl.org http://learn.perl.org/
display tail of monster file
Will it make any difference in loading time or cpu resource usage to
use the `tail' command like 'qx/tail -n30 $file/' as apposed to something
in straight perl like this example that prints the last 30 lines of $log:
#!/usr/local/bin/perl
use strict;
use warnings;
my $log = shift;
print rb($log);
sub rb {
use File::ReadBackwards;
my $log = shift;
my (@ar,$logline);
my $bw = File::ReadBackwards-new( $log ) or
die can't read $log: $! ;
my $cnt = 0;
while( defined( $logline = $bw-readline ) ) {
$cnt++ if($logline);
if($cnt = 30) {
push @ar,$logline;
}else{
last;
}
}
## reverse @ar
return reverse @ar;
}
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Re: display tail of monster file
2009/9/27 Harry Putnam rea...@newsguy.com: Will it make any difference in loading time or cpu resource usage to use the `tail' command like 'qx/tail -n30 $file/' as apposed to something in straight perl like this example that prints the last 30 lines of $log: Not absolute that which is better. But `tail` will launch an external process that is generally slower. You may benchmark them to see the difference, using the module like: http://search.cpan.org/~pangj/Net-Squid-ReverseProxy-0.02/lib/Net/Squid/ReverseProxy.pm //ye -- To unsubscribe, e-mail: beginners-unsubscr...@perl.org For additional commands, e-mail: beginners-h...@perl.org http://learn.perl.org/
Re: display tail of monster file
2009/9/27 叶孤城 gucheng...@freenet.de: 2009/9/27 Harry Putnam rea...@newsguy.com: Will it make any difference in loading time or cpu resource usage to use the `tail' command like 'qx/tail -n30 $file/' as apposed to something in straight perl like this example that prints the last 30 lines of $log: Not absolute that which is better. But `tail` will launch an external process that is generally slower. You may benchmark them to see the difference, using the module like: very sorry, copy a wrong link, the correct one: http://search.cpan.org/~dcoppit/Benchmark-Timer-0.7102/lib/Benchmark/Timer.pm -- To unsubscribe, e-mail: beginners-unsubscr...@perl.org For additional commands, e-mail: beginners-h...@perl.org http://learn.perl.org/
RE: How to implement tail -f using perl in both windows and linux !
From: Chas. Owens On Mon, Mar 23, 2009 at 14:16, Amit Saxena learn.tech...@gmail.com wrote: Is it possible to implement this without using any external modules from CPAN ? The FAQ covers this quite nicely (see below). In general you should use File::Tail[1]. And on UNIX systems, of course, you can always cheat: There are generally five reasons for not wanting to install modules: 5. the target machine is totally locked down (i.e. you login to rbash and have to provide code to a third party for inclusion on the box) Of the five, only the fifth is truly difficult to work around, but it is possible using the same techniques as the fourth with an added argument to the third party that they are willing to install other binary programs. If I may, I would like to wrap this case in a real world context. We are a certified credit card processor, commonly known as a PCI-DSS(*) level 1 Service Provider. There are specific rules about what we can and can't do on the production servers, which periodically have to pass detailed audits in order to renew our certification. In addition, there are other audits (PA-DSS) required for credit card applications we distribute to be installed on clients' computers. First of all, as a developer I am not allowed any access to the production servers, either ours or the clients'. I may not log in to them in any form. The system admins work in another department and they are only allowed to install tested and certified packages. Once the servers have passed the initial audit and are certified, every modification or addition must pass through a specific sequence of checks. First, they must undergo a thorough code review. Second, they must be packaged in an approved format for automatic installation, currently the Red Hat RPM packaging. Then that package must be installed and tested on a separate QA system. Once the QA team has approved the update, it is placed in a repository where an administrator, either here or at a client site, can check it out and install it. There are a number of reasons for this Chinese Wall between development and production, but the biggest is accountability. If I can't directly access the production servers, there is little chance that I can fiddle with the data on those servers without someone else at least detecting the intent to fiddle. Since there is real money involved, the discovery of an intent to fiddle would at least cost me my job, and could put me in prison. These rules are in place to protect the credit card issuers and are very thoroughly enforced. They also provide some liability protection for my employer, although there are additional safeguards in place for that. In the past few years there have been some highly publicized breakdowns of these rules, resulting in more scrutiny and tighter enforcement for every one else in the industry. As a result, installing a new module on the production server is very expensive. It must go through our code review and QA testing as well as being repackaged in the correct format for deployment. It is difficult to justify this expense. It would require even more effort to justify installing directly from CPAN, since none of the modules there have been through our code review nor been examined by either our QA staff or the PCI auditors. So don't talk to me about working around the limitations. The auditors will almost certainly complain about that. Tell me how to install a new module within these rules? Bob McConnell (*) PCI-DSS: Payment Card Industry - Data Security Standards -- To unsubscribe, e-mail: beginners-unsubscr...@perl.org For additional commands, e-mail: beginners-h...@perl.org http://learn.perl.org/
Re: How to implement tail -f using perl in both windows and linux !
On Tue, Mar 24, 2009 at 10:26, Bob McConnell r...@cbord.com wrote: snip As a result, installing a new module on the production server is very expensive. It must go through our code review and QA testing as well as being repackaged in the correct format for deployment. It is difficult to justify this expense. It would require even more effort to justify installing directly from CPAN, since none of the modules there have been through our code review nor been examined by either our QA staff or the PCI auditors. So don't talk to me about working around the limitations. The auditors will almost certainly complain about that. Tell me how to install a new module within these rules? Bob McConnell (*) PCI-DSS: Payment Card Industry - Data Security Standards You fall into case 5, completely locked down box (which if you recall is the one I said is difficult to work around). You have two options: 1. Follow the procedures your company had put in place for new libraries to be put on the box. 2. Provide PAR::Packer executables to QA. I have been in those environments before, and nobody seems to complain when a C programmer staticly links a library to his or her program. I see PAR::Packer as a similar beast; QA gets a monolithic binary that they can test. The question you have to ask yourself is whether it is more expensive to replicate the functionality yourself. For some modules, like the DBI, the answer is obviously yes. Remember, if you need the functionality, you still wind up writing a similar amount of code (or you wind up not implementing all of the corner cases and have buggy code), so the hit from QAing is going to happen anyway and you will have wasted the companies time and money writing, often inferior, code. Oh, and I would never suggest using CPAN (or CPANPLUS) in a such an environment. They do not provide a reliable mechanism for backing out modules. A package management system like RPM is much more preferable. I have often found that modules that are already packaged by your vendor (RedHat in this case) get a free pass in environments like this. -- Chas. Owens wonkden.net The most important skill a programmer can have is the ability to read. -- To unsubscribe, e-mail: beginners-unsubscr...@perl.org For additional commands, e-mail: beginners-h...@perl.org http://learn.perl.org/
How to implement tail -f using perl in both windows and linux !
Is it possible to implement this without using any external modules from CPAN ? Thanks Regards, Amit Saxena
Re: [PBML] How to implement tail -f using perl in both windows and linux !
Amit == Amit Saxena learn.tech...@gmail.com writes: Amit Is it possible to implement this without using any external modules from Amit CPAN ? Is it possible? Yes. Reasonable? No. Please state clearly your confusion about being able to include CPAN modules in your workflow. Hint: none of the reasons you come up with will have any ultimate validity, but I'm curious about your *particular* confusion. -- Randal L. Schwartz - Stonehenge Consulting Services, Inc. - +1 503 777 0095 mer...@stonehenge.com URL:http://www.stonehenge.com/merlyn/ Smalltalk/Perl/Unix consulting, Technical writing, Comedy, etc. etc. See http://methodsandmessages.vox.com/ for Smalltalk and Seaside discussion -- To unsubscribe, e-mail: beginners-unsubscr...@perl.org For additional commands, e-mail: beginners-h...@perl.org http://learn.perl.org/
Re: How to implement tail -f using perl in both windows and linux !
On Mon, Mar 23, 2009 at 14:16, Amit Saxena learn.tech...@gmail.com wrote:
Is it possible to implement this without using any external modules from
CPAN ?
Thanks Regards,
Amit Saxena
The FAQ covers this quite nicely (see below). In general you should
use File::Tail[1]. And on UNIX systems, of course, you can always
cheat:
#!/usr/bin/perl
use strict;
use warnings;
open my $pipe, -|, /usr/bin/tail, -f, ./file.log
or die could not start tail on file.log: $!;
print while $pipe;
There are generally five reasons for not wanting to install modules:
1. they scare you (answer, get over it)
2. they scare your sysadmins (answer, work around them by
installing in your home directory and use the lib[2] pragma)
3. you are using a hosting service that prevents you from
installing modules (answer, get a better service, there
are cheap services that don't behave like morons)
4. the target machine doesn't necessarily have the needed
module (answer, use PAR[3] or PAR::Packer[4])
5. the target machine is totally locked down (i.e. you login
to rbash and have to provide code to a third party for
inclusion on the box)
Of the five, only the fifth is truly difficult to work around, but it
is possible using the same techniques as the fourth with an added
argument to the third party that they are willing to install other
binary programs.
from perldoc -q tail[5]
First try
seek(GWFILE, 0, 1);
The statement seek(GWFILE, 0, 1) doesn’t change the current position,
but it does clear the end‐of‐file condition on the handle, so that the
next GWFILE makes Perl try again to read something.
If that doesn’t work (it relies on features of your stdio
implementation), then you need something more like this:
for (;;) {
for ($curpos = tell(GWFILE); GWFILE; $curpos =
tell(GWFILE)) {
# search for some stuff and put it into files
}
# sleep for a while
seek(GWFILE, $curpos, 0); # seek to where we had been
}
If this still doesn’t work, look into the POSIX module. POSIX defines
the clearerr() method, which can remove the end of file condition on a
filehandle. The method: read until end of file, clearerr(), read some
more. Lather, rinse, repeat.
There’s also a File::Tail module from CPAN.
1. http://search.cpan.org/dist/File-Tail/Tail.pm
2. http://perldoc.perl.org/lib.html
3. http://search.cpan.org/dist/PAR/lib/PAR.pm
4. http://search.cpan.org/dist/PAR-Packer/lib/PAR/Packer.pm
5. http://perldoc.perl.org/perlfaq5.html#How-do-I-do-a-%27tail--f%27-in-perl%3f
--
Chas. Owens
wonkden.net
The most important skill a programmer can have is the ability to read.
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perl head and tail command ?
I would imagine linux's head command can be replaced w/ chop I asked this because I have a filehandle which was, open $source, '/tmp/server.txt' ( and no doing head -1 /tmp/server.txt is not an option since I need to go through some other stuff before i need to issue below command ) and I wanted to do my $top = `head -1 $source` my $bottom = `tail -1 $source` but I realized I cannot do $source in back tick. so I imagine i can do my $top = chop $source; But what about the $bottom one? -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] http://learn.perl.org/
Re: perl head and tail command ?
Richard Lee wrote: I would imagine linux's head command can be replaced w/ chop I asked this because I have a filehandle which was, open $source, '/tmp/server.txt' ( and no doing head -1 /tmp/server.txt is not an option since I need to go through some other stuff before i need to issue below command ) and I wanted to do my $top = `head -1 $source` my $bottom = `tail -1 $source` but I realized I cannot do $source in back tick. so I imagine i can do my $top = chop $source; But what about the $bottom one? The chop() function simply removes the last character from a string and returns it. Since $source isn't a string you would get an error. Your best bet is likely to be the Tie::File module. For instance use strict; use warnings; use Tie::File; tie my @file, 'Tie::File', '/tmp/server.txt' or die $!; my ($top, $bottom) = @file[0, -1]; HTH, Rob -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] http://learn.perl.org/
Re: perl head and tail command ?
Rob Dixon wrote: Richard Lee wrote: I would imagine linux's head command can be replaced w/ chop I asked this because I have a filehandle which was, open $source, '/tmp/server.txt' ( and no doing head -1 /tmp/server.txt is not an option since I need to go through some other stuff before i need to issue below command ) and I wanted to do my $top = `head -1 $source` my $bottom = `tail -1 $source` but I realized I cannot do $source in back tick. so I imagine i can do my $top = chop $source; But what about the $bottom one? The chop() function simply removes the last character from a string and returns it. Since $source isn't a string you would get an error. Your best bet is likely to be the Tie::File module. For instance use strict; use warnings; use Tie::File; tie my @file, 'Tie::File', '/tmp/server.txt' or die $!; my ($top, $bottom) = @file[0, -1]; HTH, Rob when you are doing it to filehandle vs array, which consumes more memory? my source file is about 100,000 lines... open my $source, 'tmp/server.txt' or die !$; VS tie my @file, 'Tie::File', '/tmp/server.txt' or die $!; -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] http://learn.perl.org/
Re: perl head and tail command ?
Richard Lee wrote: Rob Dixon wrote: Richard Lee wrote: I would imagine linux's head command can be replaced w/ chop I asked this because I have a filehandle which was, open $source, '/tmp/server.txt' ( and no doing head -1 /tmp/server.txt is not an option since I need to go through some other stuff before i need to issue below command ) and I wanted to do my $top = `head -1 $source` my $bottom = `tail -1 $source` but I realized I cannot do $source in back tick. so I imagine i can do my $top = chop $source; But what about the $bottom one? The chop() function simply removes the last character from a string and returns it. Since $source isn't a string you would get an error. Your best bet is likely to be the Tie::File module. For instance use strict; use warnings; use Tie::File; tie my @file, 'Tie::File', '/tmp/server.txt' or die $!; my ($top, $bottom) = @file[0, -1]; HTH, Rob when you are doing it to filehandle vs array, which consumes more memory? my source file is about 100,000 lines... open my $source, 'tmp/server.txt' or die !$; VS tie my @file, 'Tie::File', '/tmp/server.txt' or die $!; Neither of them use any significant memory until you start reading from the file. Unless you mess about with file positioning with seek() and tell(). the only way to retrieve the last record in a file using a standard file handle is to read all the way through it one line at a time. The documentation for Tie::File says this: The file is *not* loaded into memory, so this will work even for gigantic files. So it is likely to be best for your needs. However, you should not worry about speed or memory usage until you have written the clearest program you can and then find that it consumes too many resources. HTH, Rob -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] http://learn.perl.org/
Re: perl head and tail command ?
Rob Dixon wrote: Richard Lee wrote: when you are doing it to filehandle vs array, which consumes more memory? my source file is about 100,000 lines... open my $source, 'tmp/server.txt' or die !$; VS tie my @file, 'Tie::File', '/tmp/server.txt' or die $!; Neither of them use any significant memory until you start reading from the file. Unless you mess about with file positioning with seek() and tell(). the only way to retrieve the last record in a file using a standard file handle is to read all the way through it one line at a time. The documentation for Tie::File says this: The file is *not* loaded into memory, so this will work even for gigantic files. So it is likely to be best for your needs. Actually, Tie::File seems to be very slow. http://www.mail-archive.com/beginners%40perl.org/msg93566.html However, you should not worry about speed or memory usage until you have written the clearest program you can and then find that it consumes too many resources. True. -- Gunnar Hjalmarsson Email: http://www.gunnar.cc/cgi-bin/contact.pl -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] http://learn.perl.org/
Problem in opening the file using Tail Module
Hi Guys,
I have used the following code to print the log files. but nothing is
printed even it doesn't show the warning message, no prompt is
returned.
what is the mistake in code , could u help me to find the pbm???
#!/usr/bin/perl
use strict;
use warnings;
use File::Tail;
my $file=File::Tail-new(/some/log/file/path);
while (defined(my $line=$file-read))
{
print $line;
}
Thanks,
Siva
Re: Problem in opening the file using Tail Module
I tested the codes,which run well for me.
Give a try to add '$|++' to disable IO buffer.
2007/8/29, sivasakthi [EMAIL PROTECTED]:
Hi Guys,
I have used the following code to print the log files. but nothing is
printed even it doesn't show the warning message, no prompt is
returned.
what is the mistake in code , could u help me to find the pbm???
#!/usr/bin/perl
use strict;
use warnings;
use File::Tail;
my $file=File::Tail-new(/some/log/file/path);
while (defined(my $line=$file-read))
{
print $line;
}
Thanks,
Siva
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Re: AW: Problem in opening the file using Tail Module
File::Tail is waiting at least 10 second before starting to work. if it is taking at least 10 second to start then how it is faster than using open to access the file??? On Wed, 2007-08-29 at 11:49 +0200, Angerstein wrote: File::Tail is waiting at least 10 second before starting to work. If this is not the prob, try to initalize my $line = undef; If this don´t work, you should check your file. Thanks, Siva
Re: Problem in opening the file using Tail Module
i didn't get your point , please explain little bit more...
Thanks,
Siva
On Wed, 2007-08-29 at 17:55 +0800, Jeff Pang wrote:
I tested the codes,which run well for me.
Give a try to add '$|++' to disable IO buffer.
2007/8/29, sivasakthi [EMAIL PROTECTED]:
Hi Guys,
I have used the following code to print the log files. but nothing is
printed even it doesn't show the warning message, no prompt is
returned.
what is the mistake in code , could u help me to find the pbm???
#!/usr/bin/perl
use strict;
use warnings;
use File::Tail;
my $file=File::Tail-new(/some/log/file/path);
while (defined(my $line=$file-read))
{
print $line;
}
Thanks,
Siva
Re: Problem in opening the file using Tail Module
sivasakthi wrote:
I have used the following code to print the log files. but nothing is
printed even it doesn't show the warning message, no prompt is
returned. what is the mistake in code , could u help me to find the
pbm???
#!/usr/bin/perl
use strict;
use warnings;
use File::Tail;
my $file=File::Tail-new(/some/log/file/path);
while (defined(my $line=$file-read))
{
print $line;
}
File::Tail will read only lines that are added to the file after it has been
opened. Your program will simply sleep until something new is added.
Rob
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Re: Problem in opening the file using Tail Module
On 08/29/2007 04:41 AM, sivasakthi wrote:
Hi Guys,
I have used the following code to print the log files. but nothing is
printed even it doesn't show the warning message, no prompt is
returned.
what is the mistake in code , could u help me to find the pbm???
#!/usr/bin/perl
use strict;
use warnings;
use File::Tail;
my $file=File::Tail-new(/some/log/file/path);
while (defined(my $line=$file-read))
{
print $line;
}
Thanks,
Siva
It works for me.
Maybe you want to change one of the intervals or timeouts for
File::Tail. It could be that your log file is updated infrequently.
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Re: Problem in opening the file using Tail Module
File::Tail will read only lines that are added to the file after it has been opened. Your program will simply sleep until something new is added. Rob when my log file is updated then it works correctly thanks to all for reply
AW: Problem in opening the file using Tail Module
Buffering is a problem, when you are printing to files or pipes.
The Systems don´t write everything right away to disc. It waits until it
has some time for it or the buffer is full.
If you disable buffering, you write without wait for the cost of
performance.
(if you want to write with no buffering at all you use syswrite and only
write 1 char at a time.)
-Ursprüngliche Nachricht-
Von: sivasakthi [mailto:[EMAIL PROTECTED]
Gesendet: Mittwoch, 29. August 2007 12:13
An: Jeff Pang
Cc: beginners perl
Betreff: Re: Problem in opening the file using Tail Module
i didn't get your point , please explain little bit more...
Thanks,
Siva
On Wed, 2007-08-29 at 17:55 +0800, Jeff Pang wrote:
I tested the codes,which run well for me.
Give a try to add '$|++' to disable IO buffer.
2007/8/29, sivasakthi [EMAIL PROTECTED]:
Hi Guys,
I have used the following code to print the log files. but nothing
is printed even it doesn't show the warning message, no prompt is
returned. what is the mistake in code , could u help me to find the
pbm???
#!/usr/bin/perl
use strict;
use warnings;
use File::Tail;
my $file=File::Tail-new(/some/log/file/path);
while (defined(my $line=$file-read))
{
print $line;
}
Thanks,
Siva
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AW: Problem in opening the file using Tail Module
rtfm ^^ -Ursprüngliche Nachricht- Von: sivasakthi [mailto:[EMAIL PROTECTED] Gesendet: Mittwoch, 29. August 2007 13:16 An: beginners perl Betreff: Re: Problem in opening the file using Tail Module File::Tail will read only lines that are added to the file after it has been opened. Your program will simply sleep until something new is added. Rob when my log file is updated then it works correctly thanks to all for reply -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] http://learn.perl.org/
File::Tail + JavaScript (XmlHttpRequest)
TGIF All! I hope my thread is relevant and not off-topic here. If it is, please ignore it and I apologize for taking up your time. I'm currently looking to implement a web function and an OS/X widget utilizing JavaScript's XmlHttpRequest (aka asynchronous javascript, aka AJAX). I thought at first it might make more sense to write the backend part of my script in PHP, but PHP lacks http://search.cpan.org/dist/File-Tail/Tail.pm which I'd like to use for continuous screening of a spool file. I was hoping someone could point me in the correct direction to have Perl properly speak with XmlHttpRequest. My main objective is to use AJAX functionality to speak to Perl on the backend, find me updates to the spool/log file, and push that information back to the JavaScript object which processes it and puts it into the browser. Is what I'm looking for feasible? Make sense? Thank you all, and enjoy your weekend! - sf -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] http://learn.perl.org/
monitoring file like tail -f in perl
I want to monitor a daemon's logs that updates randomly through the day and night. Is there a way to open the log file and read the new records as they come in the same way as tail -f does? Thanks Ken -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] http://learn.perl.org/ http://learn.perl.org/first-response
Re: monitoring file like tail -f in perl
Ken Foskey wrote: I want to monitor a daemon's logs that updates randomly through the day and night. Is there a way to open the log file and read the new records as they come in the same way as tail -f does? Sure, look on cpan for File::Tail::App and File::Tail -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] http://learn.perl.org/ http://learn.perl.org/first-response
Re: monitoring file like tail -f in perl
On May 29, 2006, at 18:19, Ken Foskey wrote: I want to monitor a daemon's logs that updates randomly through the day and night. Is there a way to open the log file and read the new records as they come in the same way as tail -f does? Sure, with File::Tail for example. -- fxn -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] http://learn.perl.org/ http://learn.perl.org/first-response
the 'tail' problem
hi,lists,
I have a log file which is a symbol link to the real logfile,shown as following:
$ll mssvr.log
lrwxrwxrwx1 cmail root 40 Jan 14 00:00 mssvr.log -
/home/cmail/logs/mssvr.log.2006-01-14
I have to access this file in perl script with unix 'tail -f' command.Part of
the code is below:
open (TAIL,tail -f $log|) or die can't open pipe:$!;
while(TAIL)
{
do something...
}
This script is a daemon script which run permanently.There is no problem when
in the same day.But when the date changed,the symbol link file will point to
another real logfile automatically (which decided by other application
program),such as:
lrwxrwxrwx1 cmail root 40 Jan 14 00:00 mssvr.log -
/home/cmail/logs/mssvr.log.2006-01-15
As you see,it's '2006-01-15' now, not '2006-01-14' as before.So the 'tail -f
$log' become no use for the new symbol link file,and I can't get any input from
the new logfile in the script.
How can I adjust this problem?Thanks a lot.
Jeff
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Re: the 'tail' problem
Jeff, Maybe all you have to do is make some adjustments to the pipe you're opening. Besides the well known -f switch, some tail's (like gnu tail) support -F which means a file is followed by its name and the opening is retried from time to time. From man tail (GNU): -F same as --follow=name --retry With --follow (-f), tail defaults to following the file descriptor, which means that even if a tail'ed file is renamed, tail will continue to track its end. This default behavior is not desirable when you really want to track the actual name of the file, not the file descrip- tor (e.g., log rotation). Use --follow=name in that case. That causes tail to track the named file by reopening it periodically to see if it has been removed and recreated by some other program. If you found it works for symlinks, all you have to do is use open (TAIL,tail -F $log|) or die can't open pipe:$!; Regards, Adriano Ferreira. On 1/14/06, Jeff Pang [EMAIL PROTECTED] wrote: I have a log file which is a symbol link to the real logfile,shown as following: I have to access this file in perl script with unix 'tail -f' command.Part of the code is below: open (TAIL,tail -f $log|) or die can't open pipe:$!; This script is a daemon script which run permanently.There is no problem when in the same day.But when the date changed,the symbol link file will point to another real logfile automatically (which decided by other application program),such as: [snip] How can I adjust this problem?Thanks a lot. -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] http://learn.perl.org/ http://learn.perl.org/first-response
Re: the 'tail' problem
Thanks for Adriano.I have tried the way that mentioned by you,and found it's no use for me. should the '-F' option have no effect for symlinks maybe? -Original Message- From: Adriano Ferreira [EMAIL PROTECTED] Sent: Jan 14, 2006 7:23 PM To: Jeff Pang [EMAIL PROTECTED], beginners@perl.org Subject: Re: the 'tail' problem Jeff, Maybe all you have to do is make some adjustments to the pipe you're opening. Besides the well known -f switch, some tail's (like gnu tail) support -F which means a file is followed by its name and the opening is retried from time to time. From man tail (GNU): -F same as --follow=name --retry With --follow (-f), tail defaults to following the file descriptor, which means that even if a tail'ed file is renamed, tail will continue to track its end. This default behavior is not desirable when you really want to track the actual name of the file, not the file descrip- tor (e.g., log rotation). Use --follow=name in that case. That causes tail to track the named file by reopening it periodically to see if it has been removed and recreated by some other program. If you found it works for symlinks, all you have to do is use open (TAIL,tail -F $log|) or die can't open pipe:$!; Regards, Adriano Ferreira. On 1/14/06, Jeff Pang [EMAIL PROTECTED] wrote: I have a log file which is a symbol link to the real logfile,shown as following: I have to access this file in perl script with unix 'tail -f' command.Part of the code is below: open (TAIL,tail -f $log|) or die can't open pipe:$!; This script is a daemon script which run permanently.There is no problem when in the same day.But when the date changed,the symbol link file will point to another real logfile automatically (which decided by other application program),such as: [snip] How can I adjust this problem?Thanks a lot. -- http://home.earthlink.net/~pangj/ -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] http://learn.perl.org/ http://learn.perl.org/first-response
Re: the 'tail' problem
On 1/14/06, Jeff Pang [EMAIL PROTECTED] wrote: Thanks for Adriano.I have tried the way that mentioned by you,and found it's no use for me. should the '-F' option have no effect for symlinks maybe? Well, that way would be easier if it worked. But I think with some extra logic you can do it with help of the Perl builtin readlink, which is able to give you the filename the symbolic link points to. Probably something can be written that checks to see if the link changed or not. Surely there's a CPAN module out there to help you do this. I also made a few hasty tests, and if you got hard links rather symbolic ones, it looks like tail -F would do the magic without hassle. Cheers, Adriano. -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] http://learn.perl.org/ http://learn.perl.org/first-response
Re: the 'tail' problem
Jeff Pang am Samstag, 14. Januar 2006 12.52: Thanks for Adriano.I have tried the way that mentioned by you,and found it's no use for me. should the '-F' option have no effect for symlinks maybe? -Original Message- From: Adriano Ferreira [EMAIL PROTECTED] Sent: Jan 14, 2006 7:23 PM To: Jeff Pang [EMAIL PROTECTED], beginners@perl.org Subject: Re: the 'tail' problem Jeff, Maybe all you have to do is make some adjustments to the pipe you're opening. Besides the well known -f switch, some tail's (like gnu tail) support -F which means a file is followed by its name and the opening is retried from time to time. From man tail (GNU): -F same as --follow=name --retry With --follow (-f), tail defaults to following the file descriptor, which means that even if a tail'ed file is renamed, tail will continue to track its end. This default behavior is not desirable when you really want to track the actual name of the file, not the file descrip- tor (e.g., log rotation). Use --follow=name in that case. That causes tail to track the named file by reopening it periodically to see if it has been removed and recreated by some other program. If you found it works for symlinks, all you have to do is use open (TAIL,tail -F $log|) or die can't open pipe:$!; Regards, Adriano Ferreira. On 1/14/06, Jeff Pang [EMAIL PROTECTED] wrote: I have a log file which is a symbol link to the real logfile,shown as following: I have to access this file in perl script with unix 'tail -f' command.Part of the code is below: open (TAIL,tail -f $log|) or die can't open pipe:$!; This script is a daemon script which run permanently.There is no problem when in the same day.But when the date changed,the symbol link file will point to another real logfile automatically (which decided by other application program),such as: [snip] How can I adjust this problem?Thanks a lot. Hi After reading man tail I tested tail --retry --follow=name testlog where testlog is a symlink. While this command is running, I can do (from another console): rm testlog ln -s testlog1 testlog rm testlog ln -s testlog2 testlog It does what you want. Maybe File::Tail will also do what you want, just test it (and read the man) hth joe -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] http://learn.perl.org/ http://learn.perl.org/first-response
Re: the 'tail' problem
Jeff Pang wrote:
hi,lists,
I have a log file which is a symbol link to the real logfile,shown as following:
$ll mssvr.log
lrwxrwxrwx1 cmail root 40 Jan 14 00:00 mssvr.log -
/home/cmail/logs/mssvr.log.2006-01-14
I have to access this file in perl script with unix 'tail -f' command.Part of
the code is below:
open (TAIL,tail -f $log|) or die can't open pipe:$!;
while(TAIL)
{
do something...
}
This script is a daemon script which run permanently.There is no problem when
in the same day.But when the date changed,the symbol link file will point to
another real logfile automatically (which decided by other application
program),such as:
lrwxrwxrwx1 cmail root 40 Jan 14 00:00 mssvr.log -
/home/cmail/logs/mssvr.log.2006-01-15
As you see,it's '2006-01-15' now, not '2006-01-14' as before.So the 'tail -f
$log' become no use for the new symbol link file,and I can't get any input from
the new logfile in the script.
How can I adjust this problem?Thanks a lot.
Jeff
You could try File::Tail from CPAN.
http://search.cpan.org/~mgrabnar/File-Tail-0.99.3/
http://search.cpan.org/~mgrabnar/File-Tail-0.99.3/Tail.pm
I haven't used it myself so I can't tell if it will solve your problem.
If it doesn't, you'll have to roll your own. Look up the following:
perldoc -f lstat
perldoc -f readlink
perldoc -f tell
perldoc -f seek
Basically, you would have to keep track of where you are in the file and
when the date changes, open the new file.
--
Just my 0.0002 million dollars worth,
--- Shawn
Probability is now one. Any problems that are left are your own.
SS Heart of Gold, _The Hitchhiker's Guide to the Galaxy_
* Perl tutorials at http://perlmonks.org/?node=Tutorials
* A searchable perldoc is available at http://perldoc.perl.org/
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Re: the 'tail' problem
I don't know why it can't work for me. I have tested it as following: $ln -s mssvr.log.2006-01-14 mylog $tail --follow=name --retry mylog Now this command output the content of mssvr.log.2006-01-14 correctly. So I continue to excute these commands (open another terminal): $rm -f mylog $ln -s mssvr.err mylog mssvr.err is a real file not symlink. So I expect the before command of 'tail --follow=name --retry mylog' should change to output the content of mssvr.err.But when I return to the first terminal,I found the output of 'tail' is still the content of mssvr.log.2006-01-14,not mssvr.err's. So strange it is for me. -Original Message- From: John Doe [EMAIL PROTECTED] Sent: Jan 14, 2006 8:34 AM To: beginners@perl.org Subject: Re: the 'tail' problem Jeff Pang am Samstag, 14. Januar 2006 12.52: Thanks for Adriano.I have tried the way that mentioned by you,and found it's no use for me. should the '-F' option have no effect for symlinks maybe? -Original Message- From: Adriano Ferreira [EMAIL PROTECTED] Sent: Jan 14, 2006 7:23 PM To: Jeff Pang [EMAIL PROTECTED], beginners@perl.org Subject: Re: the 'tail' problem Jeff, Maybe all you have to do is make some adjustments to the pipe you're opening. Besides the well known -f switch, some tail's (like gnu tail) support -F which means a file is followed by its name and the opening is retried from time to time. From man tail (GNU): -F same as --follow=name --retry With --follow (-f), tail defaults to following the file descriptor, which means that even if a tail'ed file is renamed, tail will continue to track its end. This default behavior is not desirable when you really want to track the actual name of the file, not the file descrip- tor (e.g., log rotation). Use --follow=name in that case. That causes tail to track the named file by reopening it periodically to see if it has been removed and recreated by some other program. If you found it works for symlinks, all you have to do is use open (TAIL,tail -F $log|) or die can't open pipe:$!; Regards, Adriano Ferreira. On 1/14/06, Jeff Pang [EMAIL PROTECTED] wrote: I have a log file which is a symbol link to the real logfile,shown as following: I have to access this file in perl script with unix 'tail -f' command.Part of the code is below: open (TAIL,tail -f $log|) or die can't open pipe:$!; This script is a daemon script which run permanently.There is no problem when in the same day.But when the date changed,the symbol link file will point to another real logfile automatically (which decided by other application program),such as: [snip] How can I adjust this problem?Thanks a lot. Hi After reading man tail I tested tail --retry --follow=name testlog where testlog is a symlink. While this command is running, I can do (from another console): rm testlog ln -s testlog1 testlog rm testlog ln -s testlog2 testlog It does what you want. Maybe File::Tail will also do what you want, just test it (and read the man) hth joe -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] http://learn.perl.org/ http://learn.perl.org/first-response -- http://home.earthlink.net/~pangj/ -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] http://learn.perl.org/ http://learn.perl.org/first-response
Re: the 'tail' problem
Jeff Pang wrote:
hi,lists,
Hello,
I have a log file which is a symbol link to the real logfile,shown as following:
$ll mssvr.log
lrwxrwxrwx1 cmail root 40 Jan 14 00:00 mssvr.log -
/home/cmail/logs/mssvr.log.2006-01-14
I have to access this file in perl script with unix 'tail -f' command.Part of
the code is below:
open (TAIL,tail -f $log|) or die can't open pipe:$!;
while(TAIL)
{
do something...
}
This script is a daemon script which run permanently.There is no problem when
in the same day.But when the date changed,the symbol link file will point to
another real logfile automatically (which decided by other application
program),such as:
lrwxrwxrwx1 cmail root 40 Jan 14 00:00 mssvr.log -
/home/cmail/logs/mssvr.log.2006-01-15
As you see,it's '2006-01-15' now, not '2006-01-14' as before.So the 'tail -f
$log' become no use for the new symbol link file,and I can't get any input from
the new logfile in the script.
How can I adjust this problem?Thanks a lot.
Have you looked at File::Tail::App? It will simplify your life a lot, if
File::Tail catches that its tailing a link and its targte changes. II
*think* it should be transparent.
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Re: the 'tail' problem
Thanks for all.I have not tried any CPAN module,since we have nearly 300 hosts
running this script,and for installing the CPAN module,I have to su to root,but
I have no that privileges.
As a tmp resolving way,I add a cron to my crontab,and restart this script at
everyday's 00:01,since the symlink get changed at 00:00.
-Original Message-
From: JupiterHost.Net [EMAIL PROTECTED]
Sent: Jan 15, 2006 1:04 AM
To: beginners@perl.org
Subject: Re: the 'tail' problem
Jeff Pang wrote:
hi,lists,
Hello,
I have a log file which is a symbol link to the real logfile,shown as
following:
$ll mssvr.log
lrwxrwxrwx1 cmail root 40 Jan 14 00:00 mssvr.log -
/home/cmail/logs/mssvr.log.2006-01-14
I have to access this file in perl script with unix 'tail -f' command.Part
of the code is below:
open (TAIL,tail -f $log|) or die can't open pipe:$!;
while(TAIL)
{
do something...
}
This script is a daemon script which run permanently.There is no problem
when in the same day.But when the date changed,the symbol link file will
point to another real logfile automatically (which decided by other
application program),such as:
lrwxrwxrwx1 cmail root 40 Jan 14 00:00 mssvr.log -
/home/cmail/logs/mssvr.log.2006-01-15
As you see,it's '2006-01-15' now, not '2006-01-14' as before.So the 'tail -f
$log' become no use for the new symbol link file,and I can't get any input
from the new logfile in the script.
How can I adjust this problem?Thanks a lot.
Have you looked at File::Tail::App? It will simplify your life a lot, if
File::Tail catches that its tailing a link and its targte changes. II
*think* it should be transparent.
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RE: Emulate tail -f on file
Thanks all for your input. The File::Tail package works although it seems to stop working once I restart the application writing to the logfile. I've played around with the settings but I'll have to take it up with the author. Thanks again! -Original Message- From: Chris Knipe [mailto:[EMAIL PROTECTED] Sent: 19 May 2005 09:48 AM To: Ramprasad A Padmanabhan Cc: beginners@perl.org Subject: Re: Emulate tail -f on file On Thu, May 19, 2005 at 11:54:35AM +0530, Ramprasad A Padmanabhan wrote: use File::Tail; On Thu, 2005-05-19 at 11:37, Tielman Koekemoer (TNE) wrote: Hi All, If I wanted to monitor a file in a way that would emulate tail -f (in the shell), how would I open the file? open(FILE, filename |); (?) TIA As someone who asked the -EXACT- same question, not even a month ago, I can really suggest the archives, and I can also really second File::Tail - it's a BRILLIANT module. -- Chris. -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] http://learn.perl.org/ http://learn.perl.org/first-response -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] http://learn.perl.org/ http://learn.perl.org/first-response
Re: Emulate tail -f on file
Because it's up-side down. Why is that? It makes replies harder to read. Why not? Please don't top-post. - Sherm Pendley, Mac OS X list Tielman Koekemoer (TNE) wrote: Thanks all for your input. The File::Tail package works although it seems to stop working once I restart the application writing to the logfile. I've played around with the settings but I'll have to take it up with the author. Thanks again! I am pretty sure that command line 'tail' has the same problem, though I suspect this is an underlying problem with the C libs if that is the case. For File::Tail you may want to check into the 'reset_tail' switch. http://danconia.org -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] http://learn.perl.org/ http://learn.perl.org/first-response
Emulate tail -f on file
Hi All, If I wanted to monitor a file in a way that would emulate tail -f (in the shell), how would I open the file? open(FILE, filename |); (?) TIA -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] http://learn.perl.org/ http://learn.perl.org/first-response
Re: Emulate tail -f on file
use File::Tail; On Thu, 2005-05-19 at 11:37, Tielman Koekemoer (TNE) wrote: Hi All, If I wanted to monitor a file in a way that would emulate tail -f (in the shell), how would I open the file? open(FILE, filename |); (?) TIA -- Netcore Solutions Pvt. Ltd. Website: http://www.netcore.co.in Spamtraps: http://cleanmail.netcore.co.in/directory.html -- -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] http://learn.perl.org/ http://learn.perl.org/first-response
Re: Emulate tail -f on file
On 5/19/05, Tielman Koekemoer (TNE) wrote: Hi All, If I wanted to monitor a file in a way that would emulate tail -f (in the shell), how would I open the file? open(FILE, filename |); (?) TIA http://perldoc.perl.org/perlfaq5.html#How-do-I-do-a-tail--f-in-perl- -- Offer Kaye -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] http://learn.perl.org/ http://learn.perl.org/first-response
Re: Emulate tail -f on file
On Thu, May 19, 2005 at 11:54:35AM +0530, Ramprasad A Padmanabhan wrote: use File::Tail; On Thu, 2005-05-19 at 11:37, Tielman Koekemoer (TNE) wrote: Hi All, If I wanted to monitor a file in a way that would emulate tail -f (in the shell), how would I open the file? open(FILE, filename |); (?) TIA As someone who asked the -EXACT- same question, not even a month ago, I can really suggest the archives, and I can also really second File::Tail - it's a BRILLIANT module. -- Chris. -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] http://learn.perl.org/ http://learn.perl.org/first-response
Re: tail -f does not exit
Rob == Rob Dixon [EMAIL PROTECTED] writes:
I got your code running nicely, although I had to make a small change due to
an older Perl (5.004) I am using:
[...]
Rob You need to close and reopen the file if you want to check for a rename.
Rob Something like the program below.
Which actually emulates tail f- nicely, since it notices a filename
change and exits, on contrary of tail -f which has to be killed.
Rob use strict;
Rob use warnings;
Rob use IO::Handle;
Rob autoflush STDOUT;
Rob use Fcntl qw(:seek);
Removed line, as seek is not yet a tag in earlier Perl.
Rob my $file = 'junk.txt';
Rob my $pos;
Rob while (1) {
Rob open LOG, $file or die Cannot open $file, $!;
Rob seek LOG, $pos, SEEK_SET if defined $pos;
seek LOG, $pos, 0 if defined $pos;
Rob print while LOG;
Rob $pos = tell LOG;
Rob close LOG;
Rob sleep 1;
Rob }
Tx a lot, Rob!
--
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tail -f does not exit
I am reading continuously a file like this:
open LOG, junk.txt or die Cannot open $file, $!\n;
while ( my $line = LOG ) {
print $line;
}
While appending lines to the file from a shell command line:
$ echo this is a new line junk.txt
Everything ok, except that I would like to find out from the Perl code
above when junk.txt has been deleted, or renamed. Unfortunately, tail
-f does not exit...
Any idea how to do that?
--
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Re: tail -f does not exit
Claude [EMAIL PROTECTED] wrote:
I am reading continuously a file like this:
open LOG, junk.txt or die Cannot open $file, $!\n;
while ( my $line = LOG ) {
print $line;
}
While appending lines to the file from a shell command line:
$ echo this is a new line junk.txt
Everything ok, except that I would like to find out from the Perl code
above when junk.txt has been deleted, or renamed. Unfortunately, tail
-f does not exit...
Any idea how to do that?
Hi Claude,
You need to close and reopen the file if you want to check for a rename.
Something like the program below.
HTH,
Rob
use strict;
use warnings;
use IO::Handle;
autoflush STDOUT;
use Fcntl qw(:seek);
my $file = 'junk.txt';
my $pos;
while (1) {
open LOG, $file or die Cannot open $file, $!;
seek LOG, $pos, SEEK_SET if defined $pos;
print while LOG;
$pos = tell LOG;
close LOG;
sleep 1;
}
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Re: tail -f does not exit
Rob == Rob Dixon [EMAIL PROTECTED] writes: [...] Rob You need to close and reopen the file if you want to check for a Rob rename. Something like the program below. [...] Tx, Rob, I'll give feedback soon here! -- Claude -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] http://learn.perl.org/ http://learn.perl.org/first-response
Re: double-log-tail
Cool, thanks - both look promising. j On Mon, 2004-01-19 at 14:47, Wiggins d'Anconia wrote: Joel Newkirk wrote: I'm interested in tailing two logs (qmail) simultaneously, and interleaving the data in something approaching chronological sequence, as well as dealing with logfile rotation gracefully. Any suggestions? Check out File::Tail on CPAN, particularly the section on 'select' and the mentioned example script, it should get you close. http://search.cpan.org/~mgrabnar/File-Tail-0.98/Tail.pm And I might as well throw a POE reference in here, as usual this sort of thing is trivial in POE, particularly since there is already a Wheel written to do it, check out the cookbook entry here (not for the faint of heart): http://poe.perl.org/?POE_Cookbook/Watching_Logs HTH, http://danconia.org -- Not all those who wander are lost. - JRR Tolkien -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] http://learn.perl.org/ http://learn.perl.org/first-response
Re: double-log-tail
Joel Newkirk wrote: I'm interested in tailing two logs (qmail) simultaneously, and interleaving the data in something approaching chronological sequence, as well as dealing with logfile rotation gracefully. Any suggestions? Check out File::Tail on CPAN, particularly the section on 'select' and the mentioned example script, it should get you close. http://search.cpan.org/~mgrabnar/File-Tail-0.98/Tail.pm And I might as well throw a POE reference in here, as usual this sort of thing is trivial in POE, particularly since there is already a Wheel written to do it, check out the cookbook entry here (not for the faint of heart): http://poe.perl.org/?POE_Cookbook/Watching_Logs HTH, http://danconia.org -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] http://learn.perl.org/ http://learn.perl.org/first-response
double-log-tail
I'm interested in tailing two logs (qmail) simultaneously, and interleaving the data in something approaching chronological sequence, as well as dealing with logfile rotation gracefully. Any suggestions? j -- Not all those who wander are lost. - JRR Tolkien -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] http://learn.perl.org/ http://learn.perl.org/first-response
Tail -f from a cgi script
Hi all My woes continue I had a great way to view system logs in real-time, all I did is direct the output of the tail command to my browser - a simple tail-f worked well. Since upgrading to RH8 and Apache 2.x this no longer works, though a tail -n20 still does. Does anyone have a way to output real-time logs to a browser? Best Regards Eugene Geldenhuys MCNE ECNE MCSE MCP TFX SOLUTIONS - PROFESSIONAL NETWORK DESIGN ,IMPLEMENTATION AND SUPPORT -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
RE: Unix ls -lrt | tail -1 in Perl
-Original Message-
From: Palmer Greg [mailto:[EMAIL PROTECTED]
Sent: Thursday, March 20, 2003 4:50 PM
To: NYIMI Jose (BMB)
Subject: RE: Unix ls -lrt | tail -1 in Perl
$filename = `ls -ltr|tail -1 $DIRECTORY`;
print $filename;
Sorry, i didn't mentioned that i wanted a pure perl solution, thanks anyway.
my $latest = (sort {-M $a = -M $b} $dir/*)[0];
Will be my way to go, thanks Sudarshan Raghavan
José.
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RE: Unix ls -lrt | tail -1 in Perl
On Fri, 21 Mar 2003, NYIMI Jose (BMB) wrote:
-Original Message-
From: Palmer Greg [mailto:[EMAIL PROTECTED]
Sent: Thursday, March 20, 2003 4:50 PM
To: NYIMI Jose (BMB)
Subject: RE: Unix ls -lrt | tail -1 in Perl
$filename = `ls -ltr|tail -1 $DIRECTORY`;
print $filename;
Sorry, i didn't mentioned that i wanted a pure perl solution, thanks anyway.
my $latest = (sort {-M $a = -M $b} $dir/*)[0];
Will be my way to go, thanks Sudarshan Raghavan
José.
The above solution will work but a more time effecient way will be to use
the Schwartzian transform as explained by Rob Hanson in his mail. Thanks
Rob :-)
The solution using while that I posted is also more time effecient than my
sort solution :-)
hth
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Re: Unix ls -lrt | tail -1 in Perl
Sudarshan Raghavan wrote:
On Fri, 21 Mar 2003, NYIMI Jose (BMB) wrote:
From: Palmer Greg [mailto:[EMAIL PROTECTED]
$filename = `ls -ltr|tail -1 $DIRECTORY`;
print $filename;
Sorry, i didn't mentioned that i wanted a pure perl solution, thanks anyway.
my $latest = (sort {-M $a = -M $b} $dir/*)[0];
Will be my way to go, thanks Sudarshan Raghavan
The above solution will work but a more time effecient way will be to use
the Schwartzian transform as explained by Rob Hanson in his mail. Thanks
Rob :-)
The solution using while that I posted is also more time effecient than my
sort solution :-)
If you want efficiency then don't use sort at all. This was about three
to four times faster on my cursory tests then then Rob's example and
about two to three times faster than using `ls -ltr|tail -1` from within
perl.
my $latest;
opendir my $dh, $dir or die Cannot open $dir: $!;
my $t = ~0;
while ( defined( my $file = readdir $dh ) ) {
if ( -f $dir/$file and -M _ $t ) {
$latest = $file;
$t = -M _;
}
}
print $latest\n;
John
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Unix ls -lrt | tail -1 in Perl
Hello, How can I do this unix command in Perl ? : ls -lrt | tail -1 Actually, i would like to get the most recent file from a given directory. Thanks in advance for your input. José. DISCLAIMER This e-mail and any attachment thereto may contain information which is confidential and/or protected by intellectual property rights and are intended for the sole use of the recipient(s) named above. Any use of the information contained herein (including, but not limited to, total or partial reproduction, communication or distribution in any form) by other persons than the designated recipient(s) is prohibited. If you have received this e-mail in error, please notify the sender either by telephone or by e-mail and delete the material from any computer. Thank you for your cooperation. For further information about Proximus mobile phone services please see our website at http://www.proximus.be or refer to any Proximus agent.
Re: Unix ls -lrt | tail -1 in Perl
On Thu, 20 Mar 2003, NYIMI Jose (BMB) wrote:
Hello,
How can I do this unix command in Perl ? : ls -lrt | tail -1
Actually, i would like to get the most recent file from a given directory.
my $latest = (sort {-M $b = -M $a} $dir/*)[-1];
or
my $latest;
while ($dir/*) {
$latest = (defined ($latest) (-M $_ -M $latest)) ? $latest : $_;
}
Remember to check for the definedness of $latest if $dir is an empty
directory
Thanks in advance for your input.
José.
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RE: Unix ls -lrt | tail -1 in Perl
If you use the first version that Sudarshan posted, you might want to use
this instead. It uses map, and is a lot faster.
my $latest = (sort {$b-{mtime} = $a-{mtime}}
map {{mtime = -M $_, file = $_}}
$dir/*)[-1];
print $latest-{file}, \n;
Benchmark results with and without using map:
Benchmark: timing 100 iterations of No-MAP, With-MAP...
No-MAP: 13 wallclock secs ( 2.43 usr 6.43 sys + 4.00 cusr 1.41 csys =
0.00 CPU)
With-MAP: 8 wallclock secs ( 1.57 usr 0.81 sys + 4.04 cusr 1.27 csys =
0.00 CPU)
Using map allows -M to be performed on each file only once (instead of once
per sort iteration). And since this is an expensive operation doing it only
once will save a lot of CPU time.
Rob
-Original Message-
From: Sudarshan Raghavan [mailto:[EMAIL PROTECTED]
Sent: Thursday, March 20, 2003 9:17 AM
To: Perl beginners
Subject: Re: Unix ls -lrt | tail -1 in Perl
On Thu, 20 Mar 2003, NYIMI Jose (BMB) wrote:
Hello,
How can I do this unix command in Perl ? : ls -lrt | tail -1
Actually, i would like to get the most recent file from a given directory.
my $latest = (sort {-M $b = -M $a} $dir/*)[-1];
or
my $latest;
while ($dir/*) {
$latest = (defined ($latest) (-M $_ -M $latest)) ? $latest : $_;
}
Remember to check for the definedness of $latest if $dir is an empty
directory
Thanks in advance for your input.
José.
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How do you code a tail -f if you're using Net::Rsh?
There's a FAQ that deals with coding a tail -f if you're logfile is on the
same box as the perl script.
But what if you want to use rsh to tail a file remotely?
Here's what I have:
--8---8---
#!/usr/bin/perl -w
use strict;
use Net::Rsh;
my $host = shift or die usage: my_rsh hostname command;
my $cmd = shift or die usage: my_rsh hostname command;
my $session = Net::Rsh - new();
my @output = $session-rsh($host, 'local_user', 'remote_user', $cmd) or
die;
for (@output) {print;}
88
---8
and here's my command line:
$ sudo my_rsh.pl hostname tail -f /u01/app/apache/logs/access_log
It seems that I never reach the print statement...
I've tried things like:
open(OUTPUT, $session-rsh($host, 'local_user', 'remote_user', $cmd) )
or die;
while (OUTPUT) {print;}
but that doesn't work.
Can anyone shed some light on this?
Thanks.
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RE: How do you code a tail -f if you're using Net::Rsh?
Richard Fernandez wrote:
There's a FAQ that deals with coding a tail -f if you're logfile is
on the same box as the perl script.
But what if you want to use rsh to tail a file remotely?
Here's what I have:
--8--
-8---
#!/usr/bin/perl -w
use strict;
use Net::Rsh;
my $host = shift or die usage: my_rsh hostname command;
my $cmd = shift or die usage: my_rsh hostname command;
my $session = Net::Rsh - new();
my @output = $session-rsh($host, 'local_user',
'remote_user', $cmd) or
die;
for (@output) {print;}
88--
--
---8
and here's my command line:
$ sudo my_rsh.pl hostname tail -f /u01/app/apache/logs/access_log
It seems that I never reach the print statement...
I've tried things like:
open(OUTPUT, $session-rsh($host, 'local_user',
'remote_user', $cmd) )
or die;
while (OUTPUT) {print;}
but that doesn't work.
The call to Net::Rsh::rsh is going to wait for the remote command to exit,
and then return the output as an array of lines. But tail -f is never going
to exit, so you need a different approach.
Try a pipe open like this:
open RSH, rsh hostname tail -f /u01/app/apache/logs/access_log |
or die $!;
print while RSH;
close RSH or die $!;
The print loop will run forever, so you'll have to interrupt your script.
The remote process will end when it tries to write the next line (it'll get
a SIGPIPE), or when the TCP keepalive detects that the client is gone.
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Re: tail + count
if (!$ARGV[0]){
die(you've forgotten to enter the file name\n);
}
if (!$ARGV[1]) {
$n = 9; # output 10 rows by default
}
else {
$n = $ARGV[1]-1;
}
what if the user enters, script.pl 8 ??? This wil try to open a file 8
and dump last 9 lines of it.
if( $#ARGV != 2){ print usage.;exit 1;}
unless ( -f $ARGV[0] ){ print bad file name ;exit 1;}
$n = $ARGV[1]-1 || 9;
- Original Message -
From: Mrtlc [EMAIL PROTECTED]
To: [EMAIL PROTECTED]
Sent: Friday, January 10, 2003 11:52 PM
Subject: tail + count
I wrote the following script as a windows tail + count function,
but it's too slow if the input is huge, how can it be improved?
if (!$ARGV[0]){
die(you've forgotten to enter the file name\n);
}
if (!$ARGV[1]) {
$n = 9; # output 10 rows by default
}
else {
$n = $ARGV[1]-1;
}
open IN, $ARGV[0] or die;
@_ = IN;
foreach my $i(($#_-$n)..$#_){
print $_[$i];
}
close IN;
$i = $#_+1;
printf ---\nTotal # of rows: $i\n;
Thanks,
Stan L
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tail + count
I wrote the following script as a windows tail + count function,
but it's too slow if the input is huge, how can it be improved?
if (!$ARGV[0]){
die(you've forgotten to enter the file name\n);
}
if (!$ARGV[1]) {
$n = 9; # output 10 rows by default
}
else {
$n = $ARGV[1]-1;
}
open IN, $ARGV[0] or die;
@_ = IN;
foreach my $i(($#_-$n)..$#_){
print $_[$i];
}
close IN;
$i = $#_+1;
printf ---\nTotal # of rows: $i\n;
Thanks,
Stan L
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Re: tail + count
Mrtlc wrote:
I wrote the following script as a windows tail + count function,
but it's too slow if the input is huge, how can it be improved?
if (!$ARGV[0]){
die(you've forgotten to enter the file name\n);
}
if (!$ARGV[1]) {
$n = 9; # output 10 rows by default
}
else {
$n = $ARGV[1]-1;
}
open IN, $ARGV[0] or die;
@_ = IN;
foreach my $i(($#_-$n)..$#_){
print $_[$i];
}
close IN;
$i = $#_+1;
printf ---\nTotal # of rows: $i\n;
A more Perlish way to do it:
use warnings;
use strict;
@ARGV == 2 and my $n = pop || 10;
$n--;
@ARGV or die you've forgotten to enter the file name\n;
my @tail;
while ( ) {
push @tail, $_;
shift @tail if @tail $n;
}
print @tail;
print ---\nTotal # of rows: $.\n;
__END__
John
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Re: tail + count
Hi John John W. Krahn [EMAIL PROTECTED] wrote in message [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... @ARGV == 2 and my $n = pop || 10; $n will be undefined if @ARGV != 2. Need something like: $n = @ARGV == 2 ? pop : 10; Rob -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
Grab last line like `tail'
Is there a perl equivalent to the unix `tail' command? Where I could grab the last line from a file without having to read the whole file? -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
Re: Grab last line like `tail'
Harry Putnam wrote: Is there a perl equivalent to the unix `tail' command? Where I could grab the last line from a file without having to read the whole file? There is the module File::ReadBackwards; # perl -MCPAN -e 'install File::ReadBackwards' $ perldoc File::ReadBackwards; bye, Da.Ta -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
Howto efficiently tail a win32 Logfile?
Hi, I need to set up a perl job which will process the lastest entries on an IIS web logfile. E.g. every (say) 5 mins, a job will run processing new additions to the file. What is the best way to go about this? Should I (when the process runs): 1) read thru the IIS logfile until I reach the desired position 2) process the new records 3) save the line number of the last (processed) record 4) exit Or will this 'lock' IIS out of writing to the file during process time (this is obviously highly undesireable) If so, should I (when the process runs): 1) take a copy of the (possibly large) logfile 2) read thru the copy until desired position reached 3) process new records 4) save last line number 5) exit Is this a better approach? Any thoughts appreciated. Regards Joel --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.401 / Virus Database: 226 - Release Date: 09/10/2002 -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
tail -f with cgi
Hi, I am trying to write a cgi program to tail -f a log file. I have a perl script that will open and print the log file, however it closes as soon as it reads whatever is in the file at that particular time. How do I mimic tail -f functionality? Thanks, Max -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
Re: tail -f with cgi
On Fri, 12 Jul 2002 08:24:55 -0400, [EMAIL PROTECTED] (Fliptop)
wrote:
Max Clark wrote:
I am trying to write a cgi program to tail -f a log file. I have a perl
script that will open and print the log file, however it closes as soon as
it reads whatever is in the file at that particular time. How do I mimic
tail -f functionality?
try the qx// operator:
my $tail = qx/tail -f filename.ext/;
print $tail;
#!/usr/bin/perl
$filename='my.log';
open( IN, $filename ) or die Couldn't open $filename: $!;
my $last;
while ( IN ) {
$last = $_;
}
print Last line is:\n$last\n;
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Re: tail -f with cgi
- Original Message -
From: Max Clark [EMAIL PROTECTED]
To: [EMAIL PROTECTED]
Sent: Thursday, July 11, 2002 6:43 PM
Subject: tail -f with cgi
Hi,
Hello Max,
I am trying to write a cgi program to tail -f a log file. I have a perl
script that will open and print the log file, however it closes as soon as
it reads whatever is in the file at that particular time. How do I mimic
tail -f functionality?
This is a quick snippet of code I threw together to view file info on a win32 platform
from the command line, that works on *nix as well. It should be easy enough to
convert to use from within a program.
use strict;
print \n\n;
my $size;
open(F,$ARGV[0]) or die Can't open $ARGV[0]: $!\n;
while(F) { $size++; }
close(F);
my ($s1,$s2)=((stat($ARGV[0]))[7],'');
for(;;){
do {
select(undef,undef,undef,0.25);
$s2=(stat($ARGV[0]))[7];
} until($s1!=$s2);
$s1=$s2;
open(F,$ARGV[0]) or die Can't open $ARGV[0]: $!\n;
my $row;
while(F) {
$row++;
print $row: $_ if($size $row);
}
$size=$row;
close(F);
}
Shawn
Thanks,
Max
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RE: tail -f with cgi
-Original Message- From: Max Clark [mailto:[EMAIL PROTECTED]] Sent: Thursday, July 11, 2002 7:44 PM To: '[EMAIL PROTECTED]' Subject: tail -f with cgi Hi, I am trying to write a cgi program to tail -f a log file. I have a perl script that will open and print the log file, however it closes as soon as it reads whatever is in the file at that particular time. How do I mimic tail -f functionality? CPAN has a File::Tail module. But a CGI script isn't designed to be long-running like this. The web server will eventually time out the request and kill your script. -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
RE: tail -f with cgi
Alright, what's a tail -f? -Original Message- From: Bob Showalter [mailto:[EMAIL PROTECTED]] Sent: Friday, July 12, 2002 11:09 AM To: 'Max Clark'; '[EMAIL PROTECTED]' Subject: RE: tail -f with cgi -Original Message- From: Max Clark [mailto:[EMAIL PROTECTED]] Sent: Thursday, July 11, 2002 7:44 PM To: '[EMAIL PROTECTED]' Subject: tail -f with cgi Hi, I am trying to write a cgi program to tail -f a log file. I have a perl script that will open and print the log file, however it closes as soon as it reads whatever is in the file at that particular time. How do I mimic tail -f functionality? CPAN has a File::Tail module. But a CGI script isn't designed to be long-running like this. The web server will eventually time out the request and kill your script. -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
Re: tail -f with cgi
- Original Message - From: Bob Showalter [EMAIL PROTECTED] To: 'Max Clark' [EMAIL PROTECTED]; [EMAIL PROTECTED] Sent: Friday, July 12, 2002 11:08 AM Subject: RE: tail -f with cgi -Original Message- From: Max Clark [mailto:[EMAIL PROTECTED]] Sent: Thursday, July 11, 2002 7:44 PM To: '[EMAIL PROTECTED]' Subject: tail -f with cgi Hi, I am trying to write a cgi program to tail -f a log file. I have a perl script that will open and print the log file, however it closes as soon as it reads whatever is in the file at that particular time. How do I mimic tail -f functionality? CPAN has a File::Tail module. But a CGI script isn't designed to be long-running like this. The web server will eventually time out the request and kill your script. I don't think he was running from the web server, but will the shell time out in the same fashion? Shawn -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
RE: tail -f with cgi
-Original Message- From: Shawn [mailto:[EMAIL PROTECTED]] Sent: Friday, July 12, 2002 12:29 PM To: Bob Showalter; 'Max Clark'; [EMAIL PROTECTED] Subject: Re: tail -f with cgi - Original Message - From: Bob Showalter [EMAIL PROTECTED] To: 'Max Clark' [EMAIL PROTECTED]; [EMAIL PROTECTED] Sent: Friday, July 12, 2002 11:08 AM Subject: RE: tail -f with cgi -Original Message- From: Max Clark [mailto:[EMAIL PROTECTED]] Sent: Thursday, July 11, 2002 7:44 PM To: '[EMAIL PROTECTED]' Subject: tail -f with cgi Hi, I am trying to write a cgi program to tail -f a log file. I have a perl script that will open and print the log file, however it closes as soon as it reads whatever is in the file at that particular time. How do I mimic tail -f functionality? CPAN has a File::Tail module. But a CGI script isn't designed to be long-running like this. The web server will eventually time out the request and kill your script. I don't think he was running from the web server, I'm just going off the phrase I am trying to write a cgi program to tail -f a log file. but will the shell time out in the same fashion? No. It continues to tail the file until interrupted (^C or whatever). -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
RE: tail -f with cgi
I found the file::tail module on cpan...
#!/usr/bin/perl -w
use File::Tail;
my $log = /usr/local/apache2/logs/access_log;
$file=File::Tail-new
(
name=$log,
interval=2,
maxinterval=10
);
while (defined($line=$file-read)) {
print $line;
}
It does exactly what I need. I can't seem to get this to work correctly
through cgi. Any ideas?
Thanks,
Max
-Original Message-
From: Max Clark [mailto:[EMAIL PROTECTED]]
Sent: Thursday, July 11, 2002 4:44 PM
To: '[EMAIL PROTECTED]'
Subject: tail -f with cgi
Hi,
I am trying to write a cgi program to tail -f a log file. I have a perl
script that will open and print the log file, however it closes as soon as
it reads whatever is in the file at that particular time. How do I mimic
tail -f functionality?
Thanks,
Max
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Re: Tail call optimization
From: Tagore Smith [EMAIL PROTECTED] Thanks :). That's great. I don't use goto much, except for a couple of very specific situations, so I hadn't read the docs for goto. It seems I missed a very interesting beast in goto NAME. In fact , I sent a friend of mine some code recently that would have been improved in one place by its use. But I still have a question :). As I understand it when tail-call optimization is done automatically there are two advantages. One is that the stack doesn't grow out of control, so that you don't have to worry about blowing it up if you recurse very deeply. The other is that the overhead of successive calls is eliminated. In theory (but, I think, often not in practice) the optimized routine should be as efficient as the equivalent iterative routine. Using goto name has the first advantage, but does it have the second? That is, does goto NAME have the same overhead as a normal call? No it does not. On the other hand most usualy it will still be slower that rewriting the code to iterative. That is ... if you assign to @_ before the goto NAME and later extract the values from it to lexical variables. Besides ... Benchmark.pm is your friend. Try it out :-) Does anyone write this kind of recursive function regularly? I mean, is it idiomatic in the more rarefied Perl circles? Or is it better (from a style point of view) to use iterative constructs even in places where recursion is more natural, but tail-call optimization would be required? I think next to noone uses this kind of recursive functions. I think I am crazy and I do have a functional language background, but still I would not use it. I know about it, but it would not come to my mind when coding normaly. In any case ... if you ever use this, please comment it heavily. Jenda === [EMAIL PROTECTED] == http://Jenda.Krynicky.cz == There is a reason for living. There must be. I've seen it somewhere. It's just that in the mess on my table ... and in my brain I can't find it. --- me -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
Re: Tail call optimization
Jenda Krynicky wrote: I believe they meant goto NAME. illuminating example snipped This way perl doesn't create a new record in the call stack every time you call the _fib(). As you can see if you comment out the return in fib_() and remove the comment from croak ... and use Carp;. (die() with stack print). See perldoc -f goto Thanks :). That's great. I don't use goto much, except for a couple of very specific situations, so I hadn't read the docs for goto. It seems I missed a very interesting beast in goto NAME. In fact , I sent a friend of mine some code recently that would have been improved in one place by its use. But I still have a question :). As I understand it when tail-call optimization is done automatically there are two advantages. One is that the stack doesn't grow out of control, so that you don't have to worry about blowing it up if you recurse very deeply. The other is that the overhead of successive calls is eliminated. In theory (but, I think, often not in practice) the optimized routine should be as efficient as the equivalent iterative routine. Using goto name has the first advantage, but does it have the second? That is, does goto NAME have the same overhead as a normal call? Does anyone write this kind of recursive function regularly? I mean, is it idiomatic in the more rarefied Perl circles? Or is it better (from a style point of view) to use iterative constructs even in places where recursion is more natural, but tail-call optimization would be required? Thanks Tagore Smith -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
Re: Tail call optimization
From: Tagore Smith [EMAIL PROTECTED]
To: [EMAIL PROTECTED]
Subject:Tail call optimization
Date sent: Tue, 28 May 2002 23:42:30 -0400
I came across this statement on the web:
Perl ... supports the tail-call optimization (although you have to do
it by
hand).
I was wondering if someone could give me an example of this. I know
what tail-call optimization means, and how to write tail-recursive
functions, in Lisp- just not sure how you would do this in Perl.
Thanks
Tagore Smith
I believe they meant goto NAME.
#use Carp;
sub fib {
die fib() defined only on positive numbers
if ($_[0] 0);
return $_[0]
if ($_[0] 3);
fib_(int($_[0]-2), 2, 1);
}
sub fib_ {
print @_\n;
my ($rest, $n, $n_1) = @_;
if ($rest = 1) {
# croak $n + $n_1
return $n + $n_1
} else {
# fib_( $rest - 1, $n + $n_1, $n);
# is replaced by
@_ = ( $rest - 1, $n + $n_1, $n);
goto fib_;
}
}
This way perl doesn't create a new record in the call stack every
time you call the _fib().
As you can see if you comment out the return in fib_() and remove
the comment from croak ... and use Carp;. (die() with stack
print).
See
perldoc -f goto
Jenda
=== [EMAIL PROTECTED] == http://Jenda.Krynicky.cz ==
There is a reason for living. There must be. I've seen it somewhere.
It's just that in the mess on my table ... and in my brain
I can't find it.
--- me
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Tail call optimization
I came across this statement on the web: Perl ... supports the tail-call optimization (although you have to do it by hand). I was wondering if someone could give me an example of this. I know what tail-call optimization means, and how to write tail-recursive functions, in Lisp- just not sure how you would do this in Perl. Thanks Tagore Smith -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
Better tail -f
Hi there,
I have got the example of trailing a file from Perl Cookbook:
---
for (;;) {
while (FH) { print $_ }
sleep 1;
seek(FH, 0, 1);
}
---
However, if another program removes (all) lines from the file referenced by
FH, perl looses the trailing (for a undetermined time). How do I improve
this code to understand the file was changed?
Cheers,
Bruno
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Re: Better tail -f
How about putting a file lock on it? That way if someone tries to access it and write to it, it will not work. -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
