RegEx Beginning of line or whitespace match

[THRAK]

I know I should be able to figure this out, but I'm kind of "code blind" at this point. I need to match "for(", but not if it is preceeded by anything other than whitespace or the beginning of the line. I can easily match the whitespace/non-whitespace, but I can't seem to figure out the "or" BOL part. Here's basic snippet of what I'm trying to do:

#!/usr/bin/perl -w

use strict;
use diagnostics;

my $line = 'some_for($var)'; #don't match
$line = '    for($var)'; #match
$line = 'for($var)'; #match

    if ($line =~ /\s+(for\()/gi) {
        print 'match';
    }

Changing \s+ to \s* obviously makes it match the BOL, but it also makes it match the non-whitespace also.

[saintmike]

Typically, the word boundary anchor \b works well in these cases:

    if($line =~ /\bfor\(/) { 
       # ...
    }

It will also match "(for(" and ";for(" which is a very common requirement for parsing programming languages. Speaking of which, if you are trying to parse perl or parts of it, check out PPI.

[THRAK]

See, I knew this wasn't as difficult to the level I was struggling with it. This works, because I forgot two additional test cases...that being that this could be anywhere in the line, not just at the beginning with or without spaces. e.g.

$line = 'could be anything here some_for($var)'; #don't match
$line = 'could be anything here for($var)'; #match

Thanks.

[CountZero]

In other words: match if for( begins at a word boundary, don't match in all other cases:

m/\b(for\()/

PS: you can drop the parentheses if you don't want to extract anything and only want to test for matches.

[eieio]

/^\s*(for\()/ should work. Use '^' to require that the match occurs at the beginning of a line rather than anywhere within the line.

[gaal]

/^\s*for\(/

This matches if the "for(" has no characters at all before it (== at beginning of line) or if there are whitespace characters. You were missing the anchor, I think.

[Frantz]

try with this :



 

if ($line =~ /(\s+|^)(for\()/gi) {
   print 'match';
}

[ZlR]

• I do not think the alternation of space with "start of line" is a good thing .
  It's not good style and it looks like it can cause problems.
  Use ^\s* instead .

• You don't need to remember the patterns so why use () to match the spaces ?

• What would the /g modifier do in such a context ? I don't like it with a start of line.

  Regards,
  ZlR.

[holli]

use strict;
use diagnostics;

my @line =
(
    'some_for($var)', #don't match
    '    for($var)',  #match
    'for($var)',      #match
);

for ( @line )
{
    print /(^(\s+)?)for\(/gi ?  "match\n" : "nomatch\n";
}

[Anonymous Monk]

Hi, simple try this

use strict;
use diagnostics;

my $line = 'some_for($var)'; #don't match
$line = '    for($var)'; #match
$line = 'for($var)'; #match


if($line =~ m#^(\s+)?for\(#si) {
    print "Match";
}
else {
    print "Non-match";
}

Gubendran.L

[gube]

Hi try this simple

use strict;
use diagnostics;

my $line = 'some_for($var)'; #don't match
$line = '    for($var)'; #match
$line = 'for($var)'; #match


if($line =~ m#^(\s+)?for\(#si) {
    print "Match";
}
else {
    print "Non-match";
}

Gubendran.L