Confess! You just stuck use strict in there to make us happy, didn't you? This script won't run at all, as is. Besides the fact that none of the variables are scoped using my or local, you forgot to put the semicolon after strict. Heheh... nice try! :-)

Also, one must wonder why you don't use CGI. Put in the slight effort to learn it... you'll be glad you did.

Now... the problem is with

print (<READTHIS>);

A filehandle, used in list context, will return all the lines it has left. Since print likes lists, the whole file gets printed out verbatim right away. Then, when you get to

while ($line = <READTHIS>) {
    if ($line =~ /cat/) {
        print "yeppers!";
    }
}
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there's nothing left.

Anyway, your while loop doesn't do what I think you think it does. The fact that you thought the regex was the problem leads me to think you actually wanted to say,

while ($line = <READTHIS>) {
    if ($line =~ /cat/) {
        print "yeppers!";
    }
    else{
        print $line;
    }
}
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and leave out,

print (<READTHIS>);

If you want to find out where your problem is, by the way, you can often do it by sticking print statements in odd places. For instance, you could have stuck one in here:

while ($line = <READTHIS>) {
    print "MOO!\n";
    if ($line =~ /cat/) {
        print "yeppers!";
    }
}
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Then, since you didn't hear a herd of cows coming through, you'd have realized that you actually weren't going through the loop at all.

P.S. Throw close READTHIS; down near the bottom, just for fun!

Yep! The main problem is with 'print (<READTHIS>);'. Once I took this out the code 'worked'.

Thanks to everyone for all the input. I have bad habits a-go-go from trying to learn this stuff too fast and I am getting sloppy.

Yep! The main problem is with 'print (<READTHIS>);'. Once I took this out the code 'worked'.

Thanks to everyone for all the input. I have bad habits a-go-go from trying to learn this stuff too fast and I am getting sloppy.

Good call on the loop, but it's still not gonna work unless you knock out print <READTHIS>; I haven't looked at it closely, but the stuff up top seems to be homemade CGI; and there's a hard-to-see space in s/~!/ ~!/g

What's wrong with the original?

It doesn't handle word boundaries, as you mention, but I don't see much of a difference between the magical assignment to $_ and the explicit assignment to $line.

Besides that, you could just use print "Yeppers!" if /cat/; and print;.

If I'm missing something here, please enlighten me.

the use of $_ was a 'code to taste' manuever on my part. I use the magical assignments all the time:)
What I saw was the file being printed out, then the while loop trying to print 'yeppers' each time cat was found.
While I was unaware that printing the file stream and then trying to call it in the while would fail, I imagined the output to be the full file printing, and then any number of 'Yeppers' one after the other. I was assuming what he wanted to do was print yeppers along with the text instead of one after the other.

All I want to do is print 'yeppers' if the output from a text file has the word 'cat'.

Ignoring the whole CGI issue, one way to do what you are asking is:

open(READTHIS, "< $readthis") or die "I can't open $readthis: $!\n";
while(<READTHIS>) {
  if (/\bcat\b/i) {
    print "yeppers!";
    last;
  }
}
close(READTHIS);
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Note that your original code forgot to add a dollar sign to the 'readthis' variable in the die statement. The \b indicates a word boundary, so that we do not grab "catalog" as pointed out above. We don't need a =~ because we are matching the default $_ created by the while(<READTHIS>) expression. The last is there so that once we find the "cat", we stop looking, and just close the file right away.