in reply to using map and swap (aka substitute)

With 5.14+, the  /r modifier can be used with  s/// substitution to achieve non-mutating substitution with return of a copy of the string (although the intermediate array creation by map noted by BrowserUk will, I think, still occur). See  s/// in the Regexp Quote-Like Operators section of perlop:

If the "/r" (non-destructive) option is used [in s///] then it runs the
substitution on a copy of the string and instead of returning
the number of substitutions, it returns the copy whether or not
a substitution occurred. The original string is never changed ...
>perl -wMstrict -le "my @list= qw(first_string second_string THIRD fourth_string); my @newlist = map s/_string$//r, @list; printf qq{'$_' } for @list; print ''; printf qq{'$_' } for @newlist; " 'first_string' 'second_string' 'THIRD' 'fourth_string' 'first' 'second' 'THIRD' 'fourth'