String substitution

[abhay180]

Why is the following substitution of $expr (with $n_expr) in $line not working?

print "BEFORE:LINE = $line,EXPR= $expr,NEW_EXPR= $n_expr\n";
$line =~ s/$expr/$n_expr/;
print "AFTER:LINE = $line,EXPR= $expr,NEW_EXPR= $n_expr\n";

The o/p of above is:
BEFORE:LINE = input [`CLW:::0] abc;,EXPR = [`CLW:::0], NEW_EXPR= [$CLW
+:0]
AFTER:LINE = input [`CLW:::0] abc;,EXPR = [`CLW:::0], NEW_EXPR= [$CLW:
+0]

The PERL-version is : V5.8.8; OS is: x86_64-linux-thread-multi

[Corion]

Your search string is interpreted as a regular expression, and it contains regular expression meta characters. See perlre. Maybe you wanted to use quotemeta or \Q|?

$line =~ s/\Q$expr/$n_expr/;

[abhay180]

Thanks a lot. That helps. Indeed i seem to have forgotten the basic rules of substitution :-)

[moritz]

Because s/// treats the first string is a regex, and not all regexes match their own textual representation. Hint: [...] has a special meaning, see perlretut.

You can avoid that with \Q$EXPR\E.