(Further to kcott's reply:)

kelscat18: Not only does the substitution you show in the OP select the wrong strings when used with grep, it changes them and also changes strings in the input array.

>perl -wMstrict -le
"my @lines = qw(aaa 111 a2a2 a2==a2 aa==aa);
 printf '@lines before: '; printf qq{'$_' } for @lines;
 print '';
 ;;
 my @words = grep(s/[^a-zA-Z0-9]/ /g, @lines);
 printf '@lines after:  '; printf  qq{'$_' } for @lines;
 print '';
 printf '@words: '; printf qq{'$_' } for @words;
 print '';
"
@lines before: 'aaa' '111' 'a2a2' 'a2==a2' 'aa==aa'
@lines after:  'aaa' '111' 'a2a2' 'a2  a2' 'aa  aa'
@words: 'a2  a2' 'aa  aa'
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