regex negation without !~

[Anonymous Monk]

Hi, I'd like to use a regex to filter out everything except a fixed string, say "accept everything except 'FOO'". I can easily do this with $str !~ /^FOO$/. But my problem is that I can't use !~, I have to use =~ because I'm passing the pattern to some other code. How do I do that?, I tried $str =~ /^^FOO$/ or /^^F^O^O$/, they certain don't do the right thing. Thanks

[imp]

You might find this discussion useful:
Negating Regexes: Tips, Tools, And Tricks Of The Trade

[RMGir]

Would

/^(?!FOO)/

do what you want? From the perlre description, it looks like a negative lookahead is exactly what you're looking for (pun somewhat intended...)

[ikegami]

Just to be clear, that doesn't work if the original expression doesn't start with ^.

>perl -le"print 'abc' !~ /b/ ?1:0"
0

>perl -le"print 'abc' =~ /^(?!b)/ ?1:0"
1

>perl -le"print 'abc' =~ /(?!b)/ ?1:0"
1

That may not be an issue in this case.

[xicheng]

check this out:

perl -wle '
  my @test = qw(FOO FOOBAR FOO AFOO FOO BARFOO FOOFOO FOO1);
  print "match: $_" for grep { /^(?!FOO$)/ } @test;
'
match: FOOBAR
match: AFOO
match: BARFOO
match: FOOFOO
match: FOO1

Regards,
Xicheng

[cengineer]

if (!($str =~ /^FOO$/)) {
 //do something for no match
}

[imp]

This approach won't work, as he is passing the regex to another module. The regex itself has to evaluate as false.