Apart from what Laurent_R mentioned, this latest version won't tell you anything about what sort of unexpected stuff is showing up in the data (my version will do that). Maybe that's not important to you in this particular process, but when I have to work with defective or unreliable input, I find that it's very helpful to be able to see what's wrong with the data.

BTW, in case my last reply wasn't clear, here's what I was talking about: 

#!/usr/bin/perl

use strict;
use warnings;

$/ = undef;     # slurp-mode for input, just in case
while ( <> ) {  # reads stdin or all file names in ARGV
    s/\s+//g;   # remove whitespace
    my $content = $_;  # keep a working copy
    tr/ACGTacgt//d;    # remove all acgt

    if ( length() ) { # anything left?
        print "$ARGV bad content: $_\n";
        do_something_with_bad_data( $ARGV, $content );
    } else {
        print "$ARGV all clean!\n";
        do_something_with_good_data( $ARGV, $content );
    }
}

sub do_something_with_bad_data
{
    my ( $filename, $data ) = @_;
# . . . fix it?  report it to someone?
}

sub do_something_with_good_data
{
    my ( $filename, $data ) = @_;
# . . . whatever you want to do
}

[download]

In reply to Re^2: =~ matches non-existent symbols by graff
in thread =~ matches non-existent symbols by Anonymous Monk

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.