How about this?

use strict;
use warnings;

while( <DATA> ) {
    if( /^(\w)='[01]$/ ) {
        print "$1 ";
    }
}
print "\n";

__DATA__
a='0
b='001
c='110
d='1
[download]

Despite your subject line mentioning "single bit", the code you present looks more like you're trying to find those strings that have only a single character consisting of 0 or 1 after the =', so that's the tack I took.

One more note: please, when posting code here, do us the courtesy of making it presentable from a formatting standpoint. The code tags (which you used) are one step. But they're the final step. An earlier step ought to be to follow some basic indentation strategy. And the step before that is to fix syntax errors such as in your while loop.

The character class is not the problem, it's that all lines have a variable name, equals, prime and either 0 or 1. But you want the line to end there; if you don't make that explicit, the regexp matches and the remainder of the line is ignored. So you have to use /(.*?)=\'[01]$/

Edit: as davido beat me to it: yes, (\w+) makes much more sense than (.*) as empty identifiers (or those of weird characters ... although I vaguely remember some HDLs can use petty uncommon chars in wire names, right?) are certainly an error.

Kudos for knowing what HDL's are. To me they're High-Density Lipoprotein. :)

The problem presented by the OP only showed single alpha-character identifiers, so I went with \w. If there's a larger set of permissible identifiers, he might use an explicit character class, and if the identifiers may be longer than a single character, he might specify a quantifier. Greediness shouldn't be an issue since I'm explicitly anchoring to the start of the line, and to ='.




Dave