A => is also called a "fat comma". It's basically a comma, but if the left hand side looks like a 'bare word', it assumes it's quoted. So, 
    system mkdir => '-p' => @dirs

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is just a fancy way of writing: 
    system 'mkdir', '-p', @dirs

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There are some people who like to use => instead of a comma to separate arguments that have different roles. 
system mkdir => '-m 775' => '-p' => @dirs;

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That indeed doesn't work. Because system has a list of arguments, no shell is involved, so mkdir is called, with -m 755 as a single argument. It should be two. Either use: 
system 'mkdir', '-m', '775', '-p', @dirs;

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or 
system mkdir => -m => 775, -p => @dirs;

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or, if you have sure @dirs doesn't contain any characters special to the shell: 
system "mkdir -m 775 -p @dirs";

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Perl --((8:>*

In reply to Re: How to build system calls using '=>' by Perl Mouse
in thread How to build system calls using '=>' by loris

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