Evaluating $1 construct in literal replacement expression

[arekfu]

O wise Perl monks,

I have written a script that parses a file and applies a number of text substitutions. I have a dictionary (let's call it %patdic) of search/substitute pairs and, for each input text line, I run something like

foreach my $search (keys %patdic) {
    s/$search/$patdic{$search}/g;
}

This works well as long as $patdic{$search} does not contain the $1 construct. Consider the following example:

#!/usr/bin/env perl

use strict;
use warnings;

$_=q{nell'amaca};
my $search=q{nell'([[:alpha:]]+a)};
my $subst='na $1';

s/$search/$subst/g;
print;
print "\n";

This will return "na $1", while I would like it to return "na amaca". Any pointers, please?

[balakrishnan]

Using eval, you can achieve your need,


$_=q{nell'amaca};
my $search=q{nell'([[:alpha:]]+a)};
my $subst='na $1';

$expr = "s/$search/".eval $subst."/g";
eval $expr;
print;
print "\n";

First we are constructing the substitution, in that using the eval, the substitute pattern is evaluated. And then the total substitution has been evaluated.

I hope this would match your requirement.

[jwkrahn]

How can I expand variables in text strings?

[Anonymous Monk]

If you mean for example expand "abc $var xyz" so that the string $var is replaced by the value of $var then eval is the only way I know.



my $var = "123";
my $str = 'abc $var def';

my $temp = eval " \"$str;\" ";

print "str2:$temp\n";

[Anonymous Monk]

You may find one of these useful s/$search/na $1/g; s/$search/sprintf '%s',"na $1"/ge;

[Anonymous Monk]

So much for previews !

#s/$search/na $1/g;

s/$search/sprintf '%s',"na $1"/ge;

[Anonymous Monk]

Pls ignore the ramblings above

This works

s/$search/$search="na $1"/ge;

[AnomalousMonk]

For a thorough discussion of this topic, see nodes printig with variables in text and simple regular expression and, with a bit of redundancy, s/// treat rhs as regex.

[gone2015]

How about:

  my $s ;
  s/$search/$subst/g and $s = $1 and s/\$1/$s/g ;