Perl FAQ 4.5

The most efficient way is using pack and unpack. This is faster than using substr. Here is a sample chunk of code to break up and put back together again some fixed-format input lines, in this case, from ps.

    # sample input line:
    #   15158 p5  T      0:00 perl /mnt/tchrist/scripts/now-what
    $ps_t = 'A6 A4 A7 A5 A*';
    open(PS, "ps|");
    $_ = ; print;
    while () {
	($pid, $tt, $stat, $time, $command) = unpack($ps_t, $_);
	for $var ('pid', 'tt', 'stat', 'time', 'command' ) {
	    print "$var: <", eval "\$$var", ">\n";
	}
	print 'line=', pack($ps_t, $pid, $tt, $stat, $time, $command),  "\n";
    }

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