substitution question

rdww has asked for the wisdom of the Perl Monks concerning the following question:

I would like to be able to pass a subsitution command into a perl program and have it work. Below is a small snippit of code that doesn't work. I am setting the substitution string and then trying to use it later. It does not subsitute anything. Any help on how to do this correctly would be appreciated... Thanks Robert

#!/bin/perl

my $SUBS='s/AA/BB/g';
$STR = "AAXXXAA";
$STR =~ $SUBS;
print "$STR\n";
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Comment on substitution question Download Code

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Re: substitution question by jkahn (Friar) on Oct 17, 2002 at 18:20 UTC
Looks like you need to use `eval`, since you have an executing context. `my $SUBS='s/AA/BB/g'; $STR = "AAXXXAA"; eval "\$STR =~ $SUBS;"; print $STR, "\n";` [download] On the other hand, if you don't like `eval`: `my $lh_sub = "AA"; my $rh_sub = "BB"; $STR = "AAXXXAA"; $STR =~ s/$lh_sub/$rh_sub/g; print $STR, "\n";` [download]	[reply] [d/l] [select]
Re: substitution question by Tanalis (Curate) on Oct 17, 2002 at 18:15 UTC
You're almost there. When you're using a regular expression, the regexp itself can't be a variable (the contents between the / delimiters can). So, for the above: `my $STR = "AAXXXAA"; $STR =~ s/AA/BB/g;` [download] Rather than assigning to the regular expression to a variable, then using the =~ operator on it, you need to apply the regular expression directly. If the contents of the regexp are going to change at runtime, you can place these into variables: `my $sub_str = "AA"; my $sub_val = "BB"; my $str = "AAXXXAA"; $str =~ s/$sub_str/$sub_val/g;` [download] Hope this helps .. --Foxcub	[reply] [d/l] [select]