Using system commands in Perl instead of built in libraries/functions [duplicate]

Question

On occasion I see people calling the system grep from Perl (and other scripting languages for that matter) instead of using the built-in language facilities/libraries to parse files. I would like to encourage people to use the built-in facilities and I want to solicit some reasons as to why it is good practice to use the built-in tools. I can think of some such as

• Using libraries/language facilities is faster. Performance suffers due to the overhead of executing external commands.
• Sticking to language facilities is more portable.

any other reasons?

On the other side of the coin, are there ever reasons to favour using system commands instead of the built-in language facilities? On that note, if a Perl script is basically only calling external commands (e.g. custom utilities without libraries), might it be better just to make a shell script of it?

Answer 1

Actually, when it matters, a specialized tool can be faster.

The real gains of keeping the work in Perl are:

• Portability (even between machines with the same OS).
• Ease of error detection.
• Flexibility in handling of errors.
• Greater customizability/flexibility.
• Fewer "moving parts". (Are you sure you correctly escaped everything and setup the environment correctly?)
• Less expertise needed. (You don't need to know both Perl and the external tools (and their ports) to code and maintain the program.)

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On that note, if a Perl script is basically only calling external commands (e.g. custom utilities without libraries), might it be better just to make a shell script of it?

Possibly. You can configure some shells to exit if any program returns an unsuccessful error code. This can make some scripts quite robust. For example, I have a couple of bash scripts featuring the line

trap 'e=$? ; echo "Error." ; exit $e' ERR