On Apr 30, 3:55 am, learn.tech...@gmail.com (Amit Saxena) wrote:
> Hello everybody,
>
> Can we perform substitution to the matched pattern inside a regular
> expression so that the modified pattern gets returned instead of earlier
> matched one ?
>
> As a reference, in the following code below, I want to perform the
> substitution of "~" character with "_" character to the value of "\3" inside
> a regular expression so that $3 ultimately becomes "are___you___fine?"
> instead of "are~~~you~~~fine?".
>
> I tried checking with the perl docs but of no help. The only hope is using
> "(?{})" which not only is experimental but also doesn't allow me to modify
> the value of "\3" inside a regular expression.
>
> Note : The reason why I want a solution entirely based on regular expression
> because this regular expression will be used in a tool which supports usage
> of perl regular expression inside its configuration file.
>
> The source code as well as the output is mentioned below.
>
> Please suggest.
>
> ==========================================================================================
>
> [r...@host1 ~]#
> [r...@host1 ~]# cat check.pl
> #!/usr/bin/perl
>
> use strict;
> use warnings;
>
> my $text1 = q/hello~~~how~~~are~~~you~~~fine?~~~OK/;
> my $regex1 = qr/^([^\~]+)\~\~\~([^\~]+)(?:\~\~\~){0,1}(.*)\~\~\~([^\~]+)$/;
>
> print "\n";
> print "text1 is [$text1]\n\n";
>
> print "regex1 is [$regex1]\n\n";
>
> if ( $text1 =~ /$regex1/ )
> {
> print "Regular expression matched\n\n";
>
> print "Field 1 : [$1]\n";
> print "Field 2 : [$2]\n";
> print "Field 3 : [$3]\n";
> print "Field 4 : [$4]\n";
>
> print "\n";}
>
> else
> {
> print "Regular expressing didn't matched\n\n";}
>
> [r...@host1 ~]#
> [r...@host1 ~]# perl check.pl
>
> text1 is [hello~~~how~~~are~~~you~~~fine?~~~OK]
>
> regex1 is [(?-xism:^([^~]+)~~~([^~]+)(?:~~~){0,1}(.*)~~~([^~]+)$)]
>
> Regular expression matched
>
> Field 1 : [hello]
> Field 2 : [how]
> Field 3 : [are~~~you~~~fine?]
> Field 4 : [OK]
Not exclusively a regex but here's an option:
my $regex1 = qr/^( # field 1 - new capture
([^~]+) # field 2
~~~
([^~]+) # field 3
(?:~~~){0,1}
) # end field 1 (needed for
length)
(.*) # target field 4
~~~
([^~]+)$ # final field 5
/x;
if ( $text1 =~ /$regex1/ )
{
( my $target = $4 ) =~ tr/~/_/;
substr( $text1, length($1), length($4), $target ); # extra
substr arg
}
orig: [hello~~~how~~~are~~~you~~~fine?~~~OK]
change: [hello~~~how~~~are___you___fine?~~~OK]
Perl 5.10 has named captures which'd make this more readable.
--
Charles DeRykus
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