perl command line parameter -MIO flag

Question

You can create a perl oneliner like this:

perl -MIO -e 'some_perl_code'

Can someone explain what this -MIO means? Couldn't find any useful information about this (On https://perldoc.perl.org/perl.html there are flags -I and -M , but this makes no sense for me).

Answer 1

Refer to perldoc perlrun for Perl command line switches:

-M module executes use module; before executing your program. This loads the module and calls its import method, causing the module to have its default effect, typically importing subroutines or giving effect to a pragma.

-MIO is interpreted as the -M option where the module name is IO . This is equivalent to using:

perl -e 'use IO; some_perl_code'

It does not use the -I option.