regex $1 not updating?
I've never encountered this before but I have to be doing something wrong. snippet of code: ]$ perl -e ' $var = Company Online (Company Systems) NETBLK-COM-5BLK (NET-24-256-0-0-1); $var =~ /.*? \(.*\) (.*?) \(.*?\)/; print $1,\n; $var = NetBlock: NETBLK-10H-6BLK; $var =~ /s\(.*?\) (.*?) \(.*?\)/; print $1,\n; ' NETBLK-COM-5BLK NETBLK-COM-5BLK Why isn't $1 getting updated with the next implicit match? It should fail but its returning the first $1 match. I can't unset $1 because it is a read-only variable. This doesn't even work if I change the second $var to $var2 because of course $1 is the same the way through. VERY frustrating. -- - Jim -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
Re: regex $1 not updating?
Jim wrote: I've never encountered this before but I have to be doing something wrong. Yes, you are. This is the documented behaviour of the numeric variables and is why we always tell beginners to use them only if the regular expression matched. snippet of code: ]$ perl -e ' $var = Company Online (Company Systems) NETBLK-COM-5BLK (NET-24-256-0-0-1); $var =~ /.*? \(.*\) (.*?) \(.*?\)/; print $1,\n; print $1\n if $var =~ /.*? \(.*\) (.*?) \(.*?\)/; $var = NetBlock: NETBLK-10H-6BLK; $var =~ /s\(.*?\) (.*?) \(.*?\)/; print $1,\n; print $1\n if $var =~ /s\(.*?\) (.*?) \(.*?\)/; ' NETBLK-COM-5BLK NETBLK-COM-5BLK Why isn't $1 getting updated with the next implicit match? It should fail but its returning the first $1 match. I can't unset $1 because it is a read-only variable. This doesn't even work if I change the second $var to $var2 because of course $1 is the same the way through. $1, $2, $3, etc. are only set on a successful match otherwise they retain the value from the previous successful match. John -- use Perl; program fulfillment -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
Re: regex $1 not updating?
Jim wrote:
I've never encountered this before but I have to be doing something
wrong.
snippet of code:
]$ perl -e '
$var = Company Online (Company Systems) NETBLK-COM-5BLK
(NET-24-256-0-0-1); $var =~ /.*? \(.*\) (.*?) \(.*?\)/;
print $1,\n;
$var = NetBlock: NETBLK-10H-6BLK;
$var =~ /s\(.*?\) (.*?) \(.*?\)/;
print $1,\n;
'
NETBLK-COM-5BLK
NETBLK-COM-5BLK
Why isn't $1 getting updated with the next implicit match? It should
fail but its returning the first $1 match. I can't unset $1 because
it is a read-only variable. This doesn't even work if I change the
second $var to $var2 because of course $1 is the same the way through.
VERY frustrating.
This is the way the $1, $2, etc. variables work. They are only set if there
is a successful match. Otherwise, they simply retain whatever previous value
they had.
You either need to test that the match worked:
if (/(\w+)/) {
# $1 is now set
print $1;
}
Or, evaluate the match in list context:
my ($word) = /(\w+)/; # $word will be undef if no match
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Re: [mail_lists] Re: regex $1 not updating?
On Friday 04 April 2003 14:34, John W. Krahn wrote:
| Jim wrote:
| I've never encountered this before but I have to be doing something
| wrong.
|
| Yes, you are. This is the documented behaviour of the numeric variables
| and is why we always tell beginners to use them only if the regular
| expression matched.
Ok. I didn't put tests in my example code. However, I do have tests in my
actual code which is what led me to this whole fiasco. In this code I am
finding that the first test ($back) pasts...and rightly so. It should.
However, in the following regex ($line) it should fail sometimes...but it
doesn't. It doesn't because when $back returns $1 as a valid return from the
regex then $1 remains a valid rval for the condition for $line. I need to
get around that!
Here is my code:
76 for $back ( @data )
77 {
78 $go_on = 1;
79
80 # start infinite loop
81
82 while ( $go_on )
83 {
84
85 # if we see that there is a net_blk
86
87 $back =~ /.*\(.*\) (.*?) .*/;
88
89 if ( $1 )
90 {
91
92 # add it to the array
93
94 push(@ret,$1);
95
96 # walk it
97 push(@done,$1);
98 my @more = get_whois($1);
99
100 # repeat process
101 for my $line ( @more )
102 {
103 $line =~ /.* \(.*\) (.*?) .*/;
104
105 if ( $1 )
106 {
107 print Pushing net_blk: $1\n;
108 push(@ret,$1);
109 }
110 else
111 {
112 print Go on to next iteration.\n;
113 $go_on = 0;
114 }
115
116 print Pushing $1 to [EMAIL PROTECTED] stack\n;
117 last if ( grep($1,@done) );
118 }
119 }
120 else
121 {
122 $go_on = 0;
123 }
124 }
125 }
|
| snippet of code:
|
| ]$ perl -e '
|
| $var = Company Online (Company Systems) NETBLK-COM-5BLK
|
| (NET-24-256-0-0-1);
|
| $var =~ /.*? \(.*\) (.*?) \(.*?\)/;
| print $1,\n;
|
| print $1\n if $var =~ /.*? \(.*\) (.*?) \(.*?\)/;
|
| $var = NetBlock: NETBLK-10H-6BLK;
| $var =~ /s\(.*?\) (.*?) \(.*?\)/;
| print $1,\n;
|
| print $1\n if $var =~ /s\(.*?\) (.*?) \(.*?\)/;
|
| '
|
| NETBLK-COM-5BLK
| NETBLK-COM-5BLK
|
| Why isn't $1 getting updated with the next implicit match? It should
| fail but its returning the first $1 match. I can't unset $1 because it
| is a read-only variable. This doesn't even work if I change the second
| $var to $var2 because of course $1 is the same the way through.
|
| $1, $2, $3, etc. are only set on a successful match otherwise they
| retain the value from the previous successful match.
|
|
| John
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- Jim
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RE: regex $1 not updating?
This feature is by design. :) -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
RE: [mail_lists] Re: regex $1 not updating?
Go back and re-read John's message. Then look at your conditionals. They are different. His work, yours don't. Yours: 87 $back =~ /.*\(.*\) (.*?) .*/; 88 89 if ( $1 ) 103 $line =~ /.* \(.*\) (.*?) .*/; 104 105 if ( $1 ) His: | print $1\n if $var =~ /.*? \(.*\) (.*?) \(.*?\)/; | print $1\n if $var =~ /s\(.*?\) (.*?) \(.*?\)/; You aren't checking to see if the REGULAR EXPRESSION SUCCEEDED. If the regular expression FAILS, then $1 retains the old value, it isn't reset. /\/\ark -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
Re: [mail_lists] Re: regex $1 not updating?
On Friday 04 April 2003 14:54, Bob Showalter wrote:
Wow! I've coding in Perl for almost three years now and I didn't this.
Anyhoo, Bob's advice was the what I used and it works now. I just moved the
regex evals into the if condition statements vs the way I was doing it.
Thanks for the assistance guys.
- Jim
| Jim wrote:
| I've never encountered this before but I have to be doing something
| wrong.
|
| snippet of code:
|
| ]$ perl -e '
|
| $var = Company Online (Company Systems) NETBLK-COM-5BLK
| (NET-24-256-0-0-1); $var =~ /.*? \(.*\) (.*?) \(.*?\)/;
| print $1,\n;
|
| $var = NetBlock: NETBLK-10H-6BLK;
| $var =~ /s\(.*?\) (.*?) \(.*?\)/;
| print $1,\n;
| '
|
| NETBLK-COM-5BLK
| NETBLK-COM-5BLK
|
|
| Why isn't $1 getting updated with the next implicit match? It should
| fail but its returning the first $1 match. I can't unset $1 because
| it is a read-only variable. This doesn't even work if I change the
| second $var to $var2 because of course $1 is the same the way through.
|
| VERY frustrating.
|
| This is the way the $1, $2, etc. variables work. They are only set if there
| is a successful match. Otherwise, they simply retain whatever previous
| value they had.
|
| You either need to test that the match worked:
|
|if (/(\w+)/) {
| # $1 is now set
| print $1;
|}
|
| Or, evaluate the match in list context:
|
|my ($word) = /(\w+)/; # $word will be undef if no match
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Re: [mail_lists] Re: regex $1 not updating?
Hi Jim.
I think yu've got a bit lost in your nexted loops. I've tried to understand what
your code does and is meant to do and have written my interpretation
below. There are a few things that I can't fathom though.
Jim wrote:
On Friday 04 April 2003 14:34, John W. Krahn wrote:
Jim wrote:
I've never encountered this before but I have to be doing something
wrong.
Yes, you are. This is the documented behaviour of the numeric variables
and is why we always tell beginners to use them only if the regular
expression matched.
Ok. I didn't put tests in my example code. However, I do have tests in my
actual code which is what led me to this whole fiasco. In this code I am
finding that the first test ($back) pasts...and rightly so. It should.
However, in the following regex ($line) it should fail sometimes...but it
doesn't. It doesn't because when $back returns $1 as a valid return from the
regex then $1 remains a valid rval for the condition for $line. I need to
get around that!
Here is my code:
76 for $back ( @data )
77 {
78 $go_on = 1;
79
80 # start infinite loop
81
82 while ( $go_on )
83 {
84
85 # if we see that there is a net_blk
86
87 $back =~ /.*\(.*\) (.*?) .*/;
88
89 if ( $1 )
90 {
91
92 # add it to the array
93
94 push(@ret,$1);
95
96 # walk it
97 push(@done,$1);
98 my @more = get_whois($1);
99
100 # repeat process
101 for my $line ( @more )
102 {
103 $line =~ /.* \(.*\) (.*?) .*/;
104
105 if ( $1 )
106 {
107 print Pushing net_blk: $1\n;
108 push(@ret,$1);
109 }
110 else
111 {
112 print Go on to next iteration.\n;
113 $go_on = 0;
114 }
115
116 print Pushing $1 to [EMAIL PROTECTED] stack\n;
117 last if ( grep($1,@done) );
118 }
119 }
120 else
121 {
122 $go_on = 0;
123 }
124 }
125 }
Take a look at this, which has something like your semantics:
foreach my $back ( @data ) {
next unless ( $back =~ /\)\s+(.+)\s+\(/ ) {
push @ret, $1;
push @done, $1;
my @more = get_whois($1);
foreach my $line ( @more ) {
if ( $line =~ /\)\s+(.+)\s+\(/ ) {
print Pushing net_blk: $1\n;
push @ret, $1;
}
}
print Pushing $1 to [EMAIL PROTECTED] stack\n;
last if ( grep($1,@done) );
}
The stack pushes are done in the equivalent place, but I think
they're not quite right; in particular the push to @ret is happening
teice. I could make neither head nor tail of your grep() call: all
I know is that it's wrong!
I hope this is a better starting point for you.
HTH,
Rob
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Re: [mail_lists] Re: regex $1 not updating?
R. Joseph Newton wrote:
from your original post raised a red flag for me:
$var =~ /.*? \(.*\) (.*?) \(.*?\)/;
I saw it, and wondered Well, what is he doing with it?. The matching function
is intended to return a true value on success, and that value is assigned to your
blandly-named $var, yet it is never used.
No, that value is NOT assigned to $var. The expression is in a void
context so the result of the expression is not assigned to anything.
You need to use the assignment operator '=' if you want to assign the
result of the expression to some variable.
Try instead:
if ($var =~ /.*? \(.*\) (.*?) \(.*?\)/;) ) {
^
That semicolon is a syntax error. It won't compile.
John
--
use Perl;
program
fulfillment
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Re: [mail_lists] Re: regex $1 not updating?
John W. Krahn wrote:
R. Joseph Newton wrote:
from your original post raised a red flag for me:
$var =~ /.*? \(.*\) (.*?) \(.*?\)/;
I saw it, and wondered Well, what is he doing with it?. The matching function
is intended to return a true value on success, and that value is assigned to your
blandly-named $var, yet it is never used.
No, that value is NOT assigned to $var. The expression is in a void
context so the result of the expression is not assigned to anything.
You need to use the assignment operator '=' if you want to assign the
result of the expression to some variable.
Try instead:
if ($var =~ /.*? \(.*\) (.*?) \(.*?\)/;) ) {
^
That semicolon is a syntax error. It won't compile.
Thanks John,
I noticed that on first scan, hence the red flag, and then I misread it while pasting
it in.
Joseph
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