Re: How to apply modifiers to a substitution via variable?

I find the suggestions to use eval EXPR unwise and suggestions to use s///ee (eval EXPR's disguised form) deplorable. Don't generate code for eval that you can't easily validate. Fortunately, eval EXPR is not needed. Here's a copy of my earlier answer to the same question.

For imsx, you can use (?switches:pattern). For g, you'll have to use an if.

my $source = "abc";
my $find = "a";
my $replace = "x";
my %opts = (
   i => 1,
   m => 0,
   s => 0,
   x => 0,
   g => 1,
);

my $opts = join '', map { $opts{$_}?$_:'' } qw( i m s x );
my $re = "(?$opts:$find)";

if ($opts{g}) {
   $source =~ s/$re/$replace/g;
} else {
   $source =~ s/$re/$replace/;
}

print $source;
[download]

Update: Fixed where %opts was referenced as %opt.

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Re^2: How to apply modifiers to a substitution via variable? by liverpole (Monsignor) on Feb 01, 2007 at 00:16 UTC
Except that, since you didn't use `strict` or `warnings`, which IMO is just as "deplorable" as using `eval`, you've got a hidden error: `use strict; use warnings; my $source = "abc"; my $find = "a"; my $replace = "x"; my %opts = ( i => 1, m => 0, s => 0, x => 0, g => 1, ); my $opts = join '', map { $opt{$_}?$_:'' } qw( i m s x ); my $re = "(?$opts:$find)"; if ($opt{g}) { $source =~ s/$re/$replace/g; } else { $source =~ s/$re/$replace/; } print $source;` [download] s''(q.S:$/9=(T1';s;(..)(..);$..=substr+crypt($1,$2),2,3;eg;print$..$/	[reply] [d/l] [select]
Re^2: How to apply modifiers to a substitution via variable? by liverpole (Monsignor) on Feb 01, 2007 at 00:18 UTC
Here's the output from ikegami's code above, (but with `strict` and `warnings` applied): `Global symbol "%opt" requires explicit package name at test.pl line 16 +. Global symbol "%opt" requires explicit package name at test.pl line 19 +. Execution of test.pl aborted due to compilation errors` [download] Update: To clarify a bit ... I don't really think that skipping `use strict;` and `use warnings;` is "deplorable". But I also don't think that sometimes using eval or the `/e` modifier to a regular expression is, either. ;-) s''(q.S:$/9=(T1';s;(..)(..);$..=substr+crypt($1,$2),2,3;eg;print$..$/	[reply] [d/l] [select]
Re^3: How to apply modifiers to a substitution via variable? by ikegami (Patriarch) on Feb 01, 2007 at 00:53 UTC
I didn't say it was tested code. And it's just a snippet to be inserted into a larger program with `use strict` and `use warnings`. And I didn't say `/e` (which is harmless), but `/ee`. If you're going to execute untrusted code, at least make it obvious. Don't hide it!	[reply] [d/l] [select]