Storing substitution patterns

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

Hi monks,

This seems like it should be straightforward, but I'm clearly missing something.I'm trying to iterate over lists of substituion REs, and the substitutions aren't substituting.

I have something like (heavily simplified):

%regexes = (first => ['(\w+) (\w+) (\w+)', '$1 $3'], 
     second => ['and so on', 'and on'] );

my $string = "big hairy mess";
foreach my $re (keys %regexes) {
     $string =~ s/$regexes{$re}[0]/$regexes{$re}[1]/i;
     print "$re: $string\n";
}
[download]

The 'first' regex, instead of printing 'first: big mess' prints 'first: $1 $3'.

I've tried adding the /e switch, which didn't help, and wrapping the backreferences in (?{}) blocks, which didn't help.

I'm sure I'm missing something stupid, but can't figure out what that might be. Hints?

Comment on Storing substitution patterns Download Code

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Re: Storing substitution patterns by Abigail-II (Bishop) on Feb 11, 2004 at 15:07 UTC
Adding `/e` tells perl to treat the replacement part as code, and execute it. The code is `$regexes{$re}[1]`. If you "execute" that, you get the same as you would interpolate it - you get `$1 $3`. What you want is to execute that. To do so, tag `/ee` (double execution) at the end, not just a `/e`. Abigail	[reply] [d/l] [select]
Re: Re: Storing substitution patterns by duff (Parson) on Feb 11, 2004 at 15:22 UTC
D'oh. Abigail is entirely correct. Though you will need to change `'$1 $3'` to something like `'qq($1 $3)'` or `'"$1 $3"'`. duff	[reply] [d/l] [select]
Re: Storing substitution patterns by abulafia (Sexton) on Feb 11, 2004 at 16:22 UTC
That was it! Thanks, Abigail. You're the best. (Didn't know one could specify /ee... that gives me all sorts of evil ideas...)	[reply]
Re: Storing substitution patterns by Fletch (Bishop) on Feb 11, 2004 at 15:07 UTC
`sub mksub (&) { my $sub = shift; return sub { local( $_ ) = $_[0]; $sub->(); $_[0]=$_ }; } %regexes = ( first => mksub { s/(\w+) (\w+) (\w+)/$1 $3/ }, second => mksub { s/and so on/and on/ }, ); my $string = "big hairy mess"; for my $re ( keys %regexes ) { $regexes{ $re }->( $string ); print "$re: $string\n"; }` [download]	[reply] [d/l]
Re: Storing substitution patterns by duff (Parson) on Feb 11, 2004 at 14:57 UTC
Strange. I would have thought that the /e modifier would do what you want. You can always wrap the entire substitution in an eval like so: `eval "\$string =~ s/$regexes{$re}[0]/$regexes{$re}[1]/i";` [download] duff	[reply] [d/l]
Re: Storing substitution patterns by Hena (Friar) on Feb 11, 2004 at 14:49 UTC
Hmm, my quess would be to make a following change `# %regexes = (first => ['(\w+) (\w+) (\w+)', '$1 $3'], # second => ['and so on', 'and on'] ); # into %regexes = (first => ["(\w+) (\w+) (\w+)", "$1 $3"], second => ["and so on", "and on"] );` [download] This is untested, so i could be wrong.	[reply] [d/l]
Re: Re: Storing substitution patterns by duff (Parson) on Feb 11, 2004 at 14:59 UTC
Nah, that will interpolate $1 and $3 into the string right then and there. That would be long before they are ever set in the substitution. duff	[reply]