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How can I manipulate fixed-record-length files?

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How can I manipulate fixed-record-length files?

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 the output of a normal, Berkeley-style ps:

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

Source: Perl FAQ: Files and Formats
Copyright: Copyright (c) 1997 Tom Christiansen and Nathan Torkington.

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