What's the difference between Perl's backticks, system, and exec?

Question

Can someone please help me? In Perl, what is the difference between:

exec "command";

and

system("command");

and

print `command`;

Are there other ways to run shell commands too?

Answer 1

exec

executes a command and never returns. It's like a return statement in a function.

If the command is not found exec returns false. It never returns true, because if the command is found it never returns at all. There is also no point in returning STDOUT, STDERR or exit status of the command. You can find documentation about it in perlfunc, because it is a function.

system

executes a command and your Perl script is continued after the command has finished.

The return value is the exit status of the command. You can find documentation about it in perlfunc.

backticks

like system executes a command and your perl script is continued after the command has finished.

In contrary to system the return value is STDOUT of the command. qx// is equivalent to backticks. You can find documentation about it in perlop, because unlike system and execit is an operator.

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Other ways

What is missing from the above is a way to execute a command asynchronously. That means your perl script and your command run simultaneously. This can be accomplished with open. It allows you to read STDOUT/STDERR and write to STDIN of your command. It is platform dependent though.

There are also several modules which can ease this tasks. There is IPC::Open2 and IPC::Open3 and IPC::Run, as well as Win32::Process::Create if you are on windows.