Re^4: Defining Characters in Word Boundary?

In your case, (?![a-z]) is what you would want to use.

One behavioral difference between these regexes and, in the case of the OP, the reason iaw4 would (probably) want to use this regex is that it can match at the end of a string and thus emulates the behavior of the \b assertion. (Note: \b can also match at the start of a string.)

>perl -wMstrict -le
"my $str = 'abcd';
 for my $rx (qr{(?=[^a-z])}, qr{(?![a-z])}, qr{\b}) {
   my @offsets;
   push @offsets, $-[1] while $str =~ m{ ($rx) }xmsg;
   if (@offsets) {
     print qq{$rx matches '$str' at offset(s) @offsets};
     }
   else {
     print qq{$rx does not match '$str'};
     }
   }
"
(?-xism:(?=[^a-z])) does not match 'abcd'
(?-xism:(?![a-z])) matches 'abcd' at offset(s) 4
(?-xism:\b) matches 'abcd' at offset(s) 0 4
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Re^5: Defining Characters in Word Boundary? by Jim (Curate) on Jan 21, 2011 at 01:06 UTC
`(?<![a-zA-Z])` emulates `\b` at the beginning of an alphabetic string and `(?![a-zA-Z])` emulates `\b` at the end of an alphabetic string. But as I explained before, it doesn't seem from iaw4's problem description that asserting a boundary match is even needed. UPDATE: Removed color.	[reply] [d/l] [select]
Re^6: Defining Characters in Word Boundary? by ikegami (Patriarch) on Jan 21, 2011 at 01:24 UTC
Needed? Not likely. But conceptually, `(?![a-zA-Z])` is simpler. With it, we're defining the macro without requiring the presence of some external context.	[reply] [d/l]