perl regex match using global switch - regex

Question

I am trying to match a word that starts with a letter and is followed by at .
I use this regex for it
use strict;
use warnings;
use Data::Dumper;
my $str = "fat 123 cat sat on the mat";
my #a = $str =~ /(\s?[a-z]{1,2}(at)\s?)/g;
print Dumper( #a );
the out put I am getting is:
$ perl ~/playground/regex.pl
$VAR1 = 'fat ';
$VAR2 = 'at';
$VAR3 = ' cat ';
$VAR4 = 'at';
$VAR5 = 'sat ';
$VAR6 = 'at';
$VAR7 = ' mat';
$VAR8 = 'at';
why does it match "at" as well when I clearly say match just 1 character before at.

Answer 1

Your optional spaces aren't a good way to delimit words: they are optional
Use the word boundary construct \b for a rough match to the ends of words
use strict;
use warnings;
use Data::Dumper;
my $str = "fat 123 cat sat on the mat";
my #aa = $str =~ /\b[a-z]+at\b/gi;
print Dumper \#aa;
output
$VAR1 = [
'fat',
'cat',
'sat',
'mat'
];
If you want to be more clever and be certain that the word found isn't preceded or followed by a non-space character then you can write this instead
my #aa = $str =~ /(?<!\S)[a-z]+at(?!\S)/gi;
which produces the same result for the data you show