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Replacing string with regexp without using modules

by cowgirl (Acolyte)
on Aug 05, 2008 at 22:34 UTC ( #702515=perlquestion: print w/replies, xml ) Need Help??
cowgirl has asked for the wisdom of the Perl Monks concerning the following question:

I am currently using this code to replace $a and $b variables from a template. However I need to make this more dynamic so I do not need to specify the values any more.
sub prog_replace_string { my $replace_this = shift; my $with_this = shift; my $string = shift; my $length = length($string); my $target = length($replace_this); for(my $i=0; $i<$length - $target + 1; $i++) { if(substr($string,$i,$target) eq $replace_this) { $string = substr($string,0,$i) . $with_this . substr($stri +ng,$i+$target); } } return $string; }
I was wondering how to do replace certain denoted names dynamically in a template file, such as in this context: <b><u><i>$var</i></u></b> and replacing this with the value of $var. I would think this would be possible by using a reference to the regexp match in a regexp like: $string = s/\$XXXXXXXX/${$1}/; Of course this does not work, I do not know what to replace XXXXXXXX with and the $1 variable would return the entire variable name, however we need it without the $ sign. This must be really easy. I would love if someone could help me out without pointing to the use of a module. Thanks a lot!

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Re: Replacing string with regexp without using modules
by pc88mxer (Vicar) on Aug 05, 2008 at 22:51 UTC
    For your first question:
    sub prog_replace_string { my ($replace_this, $with_this, $string) = @_; $string =~ s{\Q$replace_this\E}{$with_this}g; $string; }
    For your second:
    sub replace_vars { my ($string, $hash) = @_; $string =~ s{\$(\w+)}{$$hash{$1}}ge; $string; } my %vars = ( a => 1, b => 22, c => 333 ); print replace_vars('a: $a, b: $b, c: $c', \%vars);
      Thanks for the great reply. It works well. However when I cut it down to this, it doesn't work:
      $string = '$a $b $c'; $hash{a} = "go"; $string =~ s{\$(\w+)}{$$hash{$1}}ge;
      Could it be the hash reference you use to the subroutine? \$hash ? Thanks.
        Could it be the hash reference ...?

        Yes, in pc88mxer's code, $hash is a hash reference, so it must be dereferenced. In your case, it's a normal hash.  So either don't dereference

        $hash{a} = "go"; $string =~ s{\$(\w+)}{$hash{$1}}ge;

        or create a reference

        $hash->{a} = "go"; $string =~ s{\$(\w+)}{$$hash{$1}}ge;

        or even use the normal arrow syntax in both the assignment $hash->{a} = ..., and when you access it $hash->{$1}:

        $hash->{a} = "go"; $string =~ s{\$(\w+)}{$hash->{$1}}ge;

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