Take a look at shift. It says "shift ARRAY", not "shift LIST".

Look down to the nextsecond paragraph where it talks about an experimental feature that's been removed. I'm guessing the version of Perl you're using is >=v5.14 and <v5.24: so it's trying to use that experimental feature but failing because "( @_ = split /,/ )" is not an array, nor does it evaluate to an arrayref.

You can try the following with your version of Perl. I don't have a version earlier the v5.30, so I get: 

$ perl -MO=Deparse -e 'shift ( @_ = split /,/ )'
Experimental shift on scalar is now forbidden at -e line 1, near "/,/ 
+)
"
-e had compilation errors.
shift(@_ = split(/,/, $_, 0));

[download]

— Ken

In reply to Re: why can't I shift a split? by kcott
in thread why can't I shift a split? by Anonymous Monk

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.