Re: Problem using $1 in substitution command

Andreas Karlsson wrote:
Hi guys,

Hello,

I'm doing a script to search through a lot of files and doing some replacements.
It is a lot of different replacements that has to be done so I list them in a .txt
instruction file in two columns representing the strings to be matched and replaced
and the new text.
A problem arise when doing some more complex substitution, wanting to keep certain
parts of a string while replacing others. To be specific in this case I want to
remove the '' surrounding a string. The string between '' will change.

The problem comes from that I want to use the \1 (or $1) variable but since the
substitution command looks like
$line=~ s/$subst_from/$subst_to/ig;

and the $1 is incorporated into the $subst_to variable it is being populated when
the replecement string is assinged to $subst_to.
How can I keep the substitution command as general as I have it, always taking the
same to variables but still making use of the $1,...,$9 feature of Perl?
I post you a test-program which shows my problem.
List.\1 being printed after 'Result:' is the problem.

It's developed in an cygwin-environment and executes using the command
perl PerlSubstituteProblem.pl

The printouts looks like this when I run it:

Script started.
subst_to: List.\1
'' should be removed in List.'123_KeepThis_123'
$1_1: 123_KeepThis_123
$1_2: 123_KeepThis_123
Result:
'' should be removed in List.\1
Same thing but non-general s//:
'' should be removed in List.123_KeepThis_123
Changed in 1 places


________Program_______________
#!/usr/local/bin/perl
use strict;
use strict 'refs';
$|=1; #Flush ON
print "Script started.\n";

my($nr_of_changes,$line,$line_copy, $subst_from,$subst_to)=0;


$subst_from="List\\.'(\\w*)'";
$subst_to="List.\\1";
print "subst_to: $subst_to \n";

$line="'' should be removed in List.'123_KeepThis_123' \n";
print "$line";

if($line =~/$subst_from/i)
{
$line_copy=$line;
print "\$1_1: $1 \n";
$nr_of_changes++;
$line=~ s/$subst_from/$subst_to/ig;
print "\$1_2: $1 \n";
print "Result: \n";
print "$line";

print "Same thing but non-general s//: \n";
$line_copy=~ s/$subst_from/List.\1/ig;
print "$line_copy";

}

print"Changed in $nr_of_changes places\n";

exit(0);



$ perl -le'
my $subst_from = qr/(?<=List\.)\047(\w*)\047/;
my $subst_to = q/$1/;

my $line = qq/\047\047 should be removed in List.\047123_KeepThis_123\047 \n/;

print for $subst_from, $subst_to, $line;

my $nr_of_changes = $line =~ s/$subst_from/$subst_to/eeig;

print for $nr_of_changes, $line;
'
(?-xism:(?<=List\.)\047(\w*)\047)
$1
'' should be removed in List.'123_KeepThis_123'

1
'' should be removed in List.123_KeepThis_123




John
--
Perl isn't a toolbox, but a small machine shop where you can special-order
certain sorts of tools at low cost and in short order. -- Larry Wall
.

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