Re: Question on regex substitution using variables...

On Thu, 02 Feb 2006 12:26:21 -0800, Jim Gibson wrote:

In article <pan.2006.02.02.18.23.39.191334@xxxxxxxxx>, Ben Bacarisse
<ben.usenet@xxxxxxxxx> wrote:

On Thu, 02 Feb 2006 17:06:09 +0000, Ian wrote:

but where the two parts of the substitution are variables:

my $to_pattern = "(.*)\\.abc";
my $from_pattern = "\$1.def";
$f =~ s/$to_pattern/$from_pattern/;
print "$f\n";

Unfortunately this doesn't seem to work, where the first example
correctly prints out "fred.def" the second one doesn't seem to do the
back-substitution, and just prints "$1.def".
...
You need, in some sence, less quoting. One way is to re-write the
substitution as a little code block (in a string) and have it evaluated:

my $from_pattern = "\$1.'.def'";
$f =~ s/$to_pattern/eval($from_pattern)/e;

A second e modifier will force a second round of evaluation:

$f =~ s/$to_pattern/$from_pattern/ee;

Lovely! I did not know that.

This being Perl, I await news of the 1867 other ways to do it... :-)

(1866 to go :)

No, that's the one as far as I'm concerned!

FYI: this newsgroup is defunct. Try comp.lang.perl.misc in the future.

Thanks for the heads up.

--
Ben.

.