What should be done instead: 

my @list= qw(first_string second_string);
@list = map((s/_string$// and $_), @list);
print @list;

[download]

This should be done only if one wishes to reduce all strings on which no substitution is done to empty strings: 

>perl -wMstrict -le
"my @list= qw(first_string  second_string  THIRD  fourth_string);
 @list = map((s/_string$// and $_), @list);
 printf qq{'$_'  } for @list;
"
'first'  'second'  ''  'fourth'

[download]

If this is not the case, BrowserUk has shown some alternatives.

In reply to Re: using map and swap (aka substitute) by AnomalousMonk
in thread using map and swap (aka substitute) by DamianKaelGreen

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