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Perl Programming Language

FAQ 8.27 What's wrong with using backticks in a void context?


This is an excerpt from the latest version perlfaq8.pod, which
comes with the standard Perl distribution. These postings aim to
reduce the number of repeated questions as well as allow the community
to review and update the answers. The latest version of the complete
perlfaq is at http://faq.perl.org .

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8.27: What's wrong with using backticks in a void context?

    Strictly speaking, nothing. Stylistically speaking, it's not a good way
    to write maintainable code. Perl has several operators for running
    external commands. Backticks are one; they collect the output from the
    command for use in your program. The "system" function is another; it
    doesn't do this.

    Writing backticks in your program sends a clear message to the readers
    of your code that you wanted to collect the output of the command. Why
    send a clear message that isn't true?

    Consider this line:

            `cat /etc/termcap`;

    You forgot to check $? to see whether the program even ran correctly.
    Even if you wrote

            print `cat /etc/termcap`;

    this code could and probably should be written as

            system("cat /etc/termcap") == 0
            or die "cat program failed!";

    which will echo the cat command's output as it is generated, instead of
    waiting until the program has completed to print it out. It also checks
    the return value.

    "system" also provides direct control over whether shell wildcard
    processing may take place, whereas backticks do not.

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are not necessarily experts in every domain where Perl might show up,
so please include as much information as possible and relevant in any
corrections. The perlfaq-workers also don't have access to every
operating system or platform, so please include relevant details for
corrections to examples that do not work on particular platforms.
Working code is greatly appreciated.

If you'd like to help maintain the perlfaq, see the details in
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