regex search fails

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

Hi Monks, I have a little program file that's meant to search itself for lines which contain a specific word which is the first word in line 3 (ie $testVar). For some reason it does not work. Anyone clues as to how to make this work?

### this file is called regex.pl
my $testVar;
$testVar = "January";

### read this file
open(FH,"<regex.pl") or die "cannot open file";
my @myself = <FH>;
close(FH);
 
### make $pattern: $testVar
$myself[2]=~/([^ ]+)/;
my $pattern = $1;
print "Pattern: $pattern\n";

### print lines with this pattern
for(@myself)
{
  print if /$pattern/;
}
[download]

Thanks.

Comment on regex search fails Download Code

Replies are listed 'Best First'.
Re: regex search fails by jethro (Monsignor) on Mar 12, 2009 at 14:39 UTC
Change the line in the loop to `print if /\Q$pattern\E/;` [download] This is equivalent to `$pattern= quotemeata($pattern);` before the loop. The '$' in your pattern is interpreted as special char in your regex, thats why it isn't working	[reply] [d/l] [select]
Re^2: regex search fails by ikegami (Patriarch) on Mar 12, 2009 at 15:09 UTC
If the "solution" is `print if /\Q$pattern\E/;` [download] then `$pattern` doesn't contains a regexp pattern as its name implies. The variable should be renamed `my $search_str = $1; ... print if /\Q$search_str/;` [download] or `quotemeta` should be called earlier. `my $pattern = quotemeta($1); # aka "\Q$1" ... print if /$pattern/;` [download]	[reply] [d/l] [select]
Re: regex search fails by friedo (Prior) on Mar 12, 2009 at 14:41 UTC
Try `print if /\Q$pattern/`. Since your pattern contains the literal string `'$testVar'`, using the `\Q` escape will prevent it from being interpolated in the match.	[reply] [d/l] [select]
Re^2: regex search fails by stephanm (Sexton) on Mar 12, 2009 at 23:03 UTC
Thanks everyone. The \Q did the trick.	[reply]