Where's this documented?
>From Archive::Tar::File - what's '_' and where is it documented?
sub _filetype {
my $self = shift;
my $file = shift;
return unless defined $file;
return SYMLINK if (-l $file); # Symlink
return FILE if (-f _); # Plain file
return DIR if (-d _); # Directory
return FIFO if (-p _); # Named pipe
return SOCKET if (-S _); # Socket
return BLOCKDEV if (-b _); # Block special
return CHARDEV if (-c _); # Character special
### shouldn't happen, this is when making archives, not reading ###
return LONGLINK if ( $file eq LONGLINK_NAME );
return UNKNOWN; # Something else (like what?)
}
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Re: Where's this documented?
Dear Shawn,
You can use more than one file test on the same file to create a complex
logical condition.
Suppose you only want to operate on files that are both readable and writable;
you check each attribute and combine them with and:
if (-r $file and -w $file) {
...
}
Each time you perform a file test, Perl asks the filesystem for all of the
information about the file (Perl’s actually doing a stat each time, which we
talk about in the next section). Although you already got that information when
you tested -r, Perl asks for the same information again so it can test -w. What
a waste! This can be a significant performance problem if you’re testing many
attributes on many files.
The virtual filehandle _ (just the underscore) uses the information from the
last file lookup that a file test operator performed. Perl only has to look up
the file information once now:
if (-r $file and -w _) {
...
}
You don’t have to use the file tests next to each other to use _. Here we have
them in separate if conditions:
if (-r $file) {
print "The file is readable!\n";
}
if (-w _) {
print "The file is writable!\n";
}
You have to watch out that you know what the last file lookup really was,
though. If you do something else between the file tests, such as call a
subroutine, the last file you looked up might be different.
Starting with Perl 5.10, you could “stack” your file test operators by lining
them all up before the filename:
use 5.010;
if (-r -w -x -o -d $file) {
print "My directory is readable, writable, and executable!\n";
}
best,
Shaji
---
Your talent is God's gift to you. What you do with it is your gift back to God.
---
On Monday, 17 March 2014 2:35 PM, shawn wilson wrote:
>From Archive::Tar::File - what's '_' and where is it documented?
sub _filetype {
my $self = shift;
my $file = shift;
return unless defined $file;
return SYMLINK if (-l $file); # Symlink
return FILE if (-f _); # Plain file
return DIR if (-d _); # Directory
return FIFO if (-p _); # Named pipe
return SOCKET if (-S _); # Socket
return BLOCKDEV if (-b _); # Block special
return CHARDEV if (-c _); # Character special
### shouldn't happen, this is when making archives, not reading ###
return LONGLINK if ( $file eq LONGLINK_NAME );
return UNKNOWN; # Something else (like what?)
}
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Re: Where's this documented?
On Mon, Mar 17, 2014 at 10:05 AM, shawn wilson wrote:
> From Archive::Tar::File - what's '_' and where is it documented?
>
> sub _filetype {
> my $self = shift;
> my $file = shift;
>
> return unless defined $file;
>
> return SYMLINK if (-l $file); # Symlink
>
> return FILE if (-f _); # Plain file
>
> return DIR if (-d _); # Directory
>
> return FIFO if (-p _); # Named pipe
>
> return SOCKET if (-S _); # Socket
>
> return BLOCKDEV if (-b _); # Block special
>
> return CHARDEV if (-c _); # Character special
>
> ### shouldn't happen, this is when making archives, not reading ###
> return LONGLINK if ( $file eq LONGLINK_NAME );
>
> return UNKNOWN; # Something else (like what?)
>
> }
>
Try 'perldoc -f -X' or http://perldoc.perl.org/functions/-X.html
In particular, the section that starts (in 5.18 at least) with 'If any of
the file tests'
Re: Where's this documented?
Thank y'all.
That's weird to read, but it makes sense easy enough.
On Mon, Mar 17, 2014 at 7:10 AM, Brian Fraser wrote:
> On Mon, Mar 17, 2014 at 10:05 AM, shawn wilson wrote:
>>
>> From Archive::Tar::File - what's '_' and where is it documented?
>>
>> sub _filetype {
>> my $self = shift;
>> my $file = shift;
>>
>> return unless defined $file;
>>
>> return SYMLINK if (-l $file); # Symlink
>>
>> return FILE if (-f _); # Plain file
>>
>> return DIR if (-d _); # Directory
>>
>> return FIFO if (-p _); # Named pipe
>>
>> return SOCKET if (-S _); # Socket
>>
>> return BLOCKDEV if (-b _); # Block special
>>
>> return CHARDEV if (-c _); # Character special
>>
>> ### shouldn't happen, this is when making archives, not reading ###
>> return LONGLINK if ( $file eq LONGLINK_NAME );
>>
>> return UNKNOWN; # Something else (like what?)
>>
>> }
>
>
> Try 'perldoc -f -X' or http://perldoc.perl.org/functions/-X.html
>
> In particular, the section that starts (in 5.18 at least) with 'If any of
> the file tests'
>
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Re: Where's this documented?
Shaji Kalidasan wrote:
You can use more than one file test on the same file to create a
complex logical condition.
Suppose you only want to operate on files that are both readable and
writable; you check each attribute and combine them with and:
if (-r $file and -w $file) {
...
}
Each time you perform a file test
or use stat() or lstat()
, Perl asks the filesystem for all of
the information about the file (Perl’s actually doing a stat each time,
which we talk about in the next section). Although you already got that
information when you tested -r, Perl asks for the same information
again so it can test -w. What a waste! This can be a significant
performance problem if you’re testing many attributes on many files.
The virtual filehandle _ (just the underscore) uses the information
from the last file lookup that a file test operator
or stat() or lstat()
performed. Perl
only has to look up the file information once now:
John
--
Any intelligent fool can make things bigger and
more complex... It takes a touch of genius -
and a lot of courage to move in the opposite
direction. -- Albert Einstein
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Re: Where's this documented?
On Tue, Mar 18, 2014 at 11:32 PM, John W. Krahn wrote: > Shaji Kalidasan wrote: > > or stat() or lstat() I don't remember seeing that reusing i?stat would not duplicate the stat call...? -- To unsubscribe, e-mail: beginners-unsubscr...@perl.org For additional commands, e-mail: beginners-h...@perl.org http://learn.perl.org/
Re: Where's this documented?
shawn wilson wrote: Oh, I guess I was thinking that using the file name repeats the stat (which it does). Since I was complaining about the ugliness of '_'. However, you're right - that works as well as (-f _)<-- that doesn't look weird as shit? I've got issues moving my fingers into typing that Whatever, y'all answered my question and I learned something (though damn them for not just making another perlvar or something else to do this) - I appreciate the help/info. _ is a perlvar. It is part of the typeglob that includes $_, @_, %_ and &_. perldoc perldata perldoc perlmod perldoc perlref John -- Any intelligent fool can make things bigger and more complex... It takes a touch of genius - and a lot of courage to move in the opposite direction. -- Albert Einstein -- To unsubscribe, e-mail: beginners-unsubscr...@perl.org For additional commands, e-mail: beginners-h...@perl.org http://learn.perl.org/
Re[2]: Where's this documented?
From perldoc -f stat:
If "stat" is passed the special filehandle consisting of an underline, no stat
is done, but the current
contents of the stat structure from the last "stat", "lstat", or filetest are
returned. Example:
if (-x $file && (($d) = stat(_)) && $d < 0) {
print "$file is executable NFS file\n";
}
(This works on machines only for which the device number is negative under NFS.)
We are looking for openstack and python developers.
Please check: http://www.nsbeta.info/jobs
Wed, 19 Mar 2014 01:44:15 -0400 from shawn wilson :
>On Tue, Mar 18, 2014 at 11:32 PM, John W. Krahn < jwkr...@shaw.ca > wrote:
>> Shaji Kalidasan wrote:
>
>>
>> or stat() or lstat()
>
>I don't remember seeing that reusing i?stat would not duplicate the
>stat call...?
>
>--
>To unsubscribe, e-mail: beginners-unsubscr...@perl.org
>For additional commands, e-mail: beginners-h...@perl.org
>http://learn.perl.org/
>
>
Re: Re[2]: Where's this documented?
On Wed, Mar 19, 2014 at 4:21 AM, Yonghua Peng wrote:
> From perldoc -f stat:
>
> If "stat" is passed the special filehandle consisting of an underline, no
> stat is done, but the current
> contents of the stat structure from the last "stat", "lstat", or filetest
> are returned. Example:
>
> if (-x $file && (($d) = stat(_)) && $d < 0) {
> print "$file is executable NFS file\n";
> }
>
> (This works on machines only for which the device number is negative under
> NFS.)
>
>
>
>
> We are looking for openstack and python developers.
> Please check: http://www.nsbeta.info/jobs
>
> Wed, 19 Mar 2014 01:44:15 -0400 from shawn wilson :
>
> On Tue, Mar 18, 2014 at 11:32 PM, John W. Krahn wrote:
>> Shaji Kalidasan wrote:
>
>>
>> or stat() or lstat()
>
> I don't remember seeing that reusing i?stat would not duplicate the
> stat call...?
>
Oh, I guess I was thinking that using the file name repeats the stat
(which it does). Since I was complaining about the ugliness of '_'.
However, you're right - that works as well as (-f _) <-- that doesn't
look weird as shit? I've got issues moving my fingers into typing
that Whatever, y'all answered my question and I learned something
(though damn them for not just making another perlvar or something
else to do this) - I appreciate the help/info.
--
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Re: Re[2]: Where's this documented?
On Wed, Mar 19, 2014 at 10:37 AM, shawn wilson wrote:
> On Wed, Mar 19, 2014 at 4:21 AM, Yonghua Peng wrote:
> > From perldoc -f stat:
> >
> > If "stat" is passed the special filehandle consisting of an underline, no
> > stat is done, but the current
> > contents of the stat structure from the last "stat", "lstat", or filetest
> > are returned. Example:
> >
> > if (-x $file && (($d) = stat(_)) && $d < 0) {
> > print "$file is executable NFS file\n";
> > }
> >
> > (This works on machines only for which the device number is negative
> under
> > NFS.)
> >
> >
> >
> >
> > We are looking for openstack and python developers.
> > Please check: http://www.nsbeta.info/jobs
> >
> > Wed, 19 Mar 2014 01:44:15 -0400 from shawn wilson :
> >
> > On Tue, Mar 18, 2014 at 11:32 PM, John W. Krahn wrote:
> >> Shaji Kalidasan wrote:
> >
> >>
> >> or stat() or lstat()
> >
> > I don't remember seeing that reusing i?stat would not duplicate the
> > stat call...?
> >
>
> Oh, I guess I was thinking that using the file name repeats the stat
> (which it does). Since I was complaining about the ugliness of '_'.
> However, you're right - that works as well as (-f _) <-- that doesn't
> look weird as shit? I've got issues moving my fingers into typing
> that Whatever, y'all answered my question and I learned something
> (though damn them for not just making another perlvar or something
> else to do this)
If you don't like it, then put your time where your mouth is: Perl is open
source, patches are always welcome.
