Re^3: Regex match on implicit default variable ($

Hello Todd,

Here’s another approach, using the /g modifier in scalar context and relying on the fact that . in a regex matches any character except a newline:

use strict;
use warnings;

my $A = "abc\ndef\nghi\n";

while ($A =~ /(.+)/g)
{
    print "$1\n" unless $1 =~ /def/;
}
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Output:

13:59 >perl 1419_SoPW.pl
abc
ghi

14:00 >
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Hope that helps,

Athanasius <°(((>< contra mundum Iustus alius egestas vitae, eros Piratica,

Comment on Re^3: Regex match on implicit default variable ($_) in a script, not a one liner Select or Download Code

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Re^4: Regex match on implicit default variable ($_) in a script, not a one liner
by Todd Chester (Scribe) on Oct 24, 2015 at 05:15 UTC

I am now able to exclude and reform $B, but I can't do it the other way (include only "def"). Isn't "while" suppose to be the opposite of "until"?

#!/usr/bin/perl

use strict;
use warnings;
use diagnostics;

my $B = "";
my $A = "abc
def
ghi
";

while ( $A =~ m{(.+)}g ) {
   $B .= "$1\n" unless $1 =~ /def/;
}
print "\$B = \n$B\n";


$B = "";
while ( $A =~ m{(.+)}g ) {
   $B .= "$1\n" while $1 =~ /def/;
}
print "\$B = \n$B\n";
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$B =

abc

ghi

Now what am I doing wrong?

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[d/l]

Re^5: Regex match on implicit default variable ($_) in a script, not a one liner

by Athanasius (Cardinal) on Oct 24, 2015 at 06:20 UTC

Isn't "while" suppose to be the opposite of "until"?

Yes, but you want the “opposite” (actually, the negation) of unless, which is simply if. See perlsyn#Statement-Modifiers.

But there is another problem: $1 refers to the first capture in the most recent regular expression match. In the expression:

$B .= "$1\n" unless $1 =~ /def/;
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the concatenation $B .= "$1\n" occurs only if the regex match $1 ~ /def/ fails; in which case, there is no match, so the most recent match is still the one from the while loop regex. But in the expression:

$B .= "$1\n" if $match =~ /def/;
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the concatenation occurs only if the new match succeeds; in which case, $1 is overwritten. You can fix this by assigning the value of $1 to a temporary variable:

while ($A =~ m{(.+)}g)
{
    my $capture = $1;
    $B .= "$capture\n" if $capture =~ /def/;
}
[download]

Hope that helps,

Athanasius <°(((>< contra mundum Iustus alius egestas vitae, eros Piratica,

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[d/l]
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Re^4: Regex match on implicit default variable ($_) in a script, not a one liner
by Todd Chester (Scribe) on Oct 24, 2015 at 04:52 UTC

I am trying to create a multiline $B from $A. How do I reassemble $B?

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