You are viewing the version of this documentation from Perl 5.31.5. This is a development release of Perl.
join EXPR,LIST

Joins the separate strings of LIST into a single string with fields separated by the value of EXPR, and returns that new string. Example:

my $rec = join(':', $login,$passwd,$uid,$gid,$gcos,$home,$shell);

Beware that unlike split, join doesn't take a pattern as its first argument. Compare split.