in reply to match whitespace or beginning/end of string

What's wrong with \b? It's only needed at the beginning, since you have the closing quote to mark the end. (UPDATED below with fancier pattern)

Test code: 

#!/usr/bin/perl
use strict;
use warnings;
use diagnostics;

my $alpha = qq(alpha="first");
my $beta  = qq(beta="second");
my $gamma = qq(gamma="third");

my $s1 = qq($alpha $beta $gamma);
my $s2 = qq($alpha $gamma $beta);
my $s3 = qq($beta $alpha $gamma);

#my $pat = qr/\b(beta="second")/;
my $pat = qr/(?:\A|\s)(beta="second")(?:\s|\Z)/;

print "s1: \'$s1\', match=".($s1 =~ $pat ? $1 : "nada")."\n";
print "s2: \'$s2\', match=".($s2 =~ $pat ? $1 : "nada")."\n";
print "s3: \'$s3\', match=".($s3 =~ $pat ? $1 : "nada")."\n";

[download]
Produces: 
s1: 'alpha="first" beta="second" gamma="third"', match=beta="second"
s2: 'alpha="first" gamma="third" beta="second"', match=beta="second"
s3: 'beta="second" alpha="first" gamma="third"', match=beta="second"

[download]
Updated: Removed half the test cases, since there's really only 3 possibilities. Also added fancy pattern that ensures either start/end of string or space is present.

Replies are listed 'Best First'.
Re^2: match whitespace or beginning/end of string
by azadian (Sexton) on Oct 30, 2009 at 13:17 UTC
    Works fine for beta, but the same code would not work for alpha. The point is, I don't know the location in the string of the word I'm matching. You're right that, in this case, I don't need to worry about the end of string. But still, I'd like to be able to give my users a general-purpose rule which works even without the quotes.
[reply]
      See updated code above using fancier pattern. (Why do you think think the original would not work for alpha?)
[reply]
        Yes, the improved code is fine, and covers all cases. However, the goal is to have code which is fine and covers all cases AND IS SIMPLER. I want simple because I need to recommend this to testers who don't know necessarily know what a regular expression is. I can tell them to stick in a \b at the beginning and end of each word to be matched, and I can even explain it to them. Unfortunately, \b doesn't always work. The more complicated expressions such as you used (and I suggested) are not so easy to recommend or explain. I just want to know if there is some simple way to do what seems like a simple task.
[reply]

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