P
PerlFAQ Server
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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The perlfaq-workers, a group of volunteers, maintain the perlfaq. They
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
perlfaq.pod.
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 .
--------------------------------------------------------------------
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.
--------------------------------------------------------------------
The perlfaq-workers, a group of volunteers, maintain the perlfaq. They
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
perlfaq.pod.