A historic example of string eval that springs to mind is Larry's famous rename script. See also Unix rename faq (a version of Larry's script is given at the end) and the Perl Cookbook, recipe 9.9.

And though these may set a poor example for newbies, please notice that Acme::Bleach:

do {eval brighten $shirt; exit} unless dirty $shirt && not dress $shir
+t;
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do {eval unslay $demon; exit} unless evil $demon && not punch $demon;
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eval eval '"'.
                   ("\["^
    '+').        ('['^')')
.('`'|')')      .('`'|'.').
 ('['^'/').    ('{'^'[').''.
   ('\\').   '"'.('`'|"\(").(
  '`'|'%') .('`'|',').('`'|','
  ).('`'| '/').('{'^'[').("\["^
  ',').('`'|'/').('['^')').('`'
   |',').('`'|'$').'\\'.('\\').(
   '`'|'.').'\\'.'"'.';'.('!'^'+'
    ).'"';$:='.'^'~';$~='@'|"\(";
     $^=')'^'[';$/='`'|'.';$,= ((
       (( '('))))^'}';$\= '`'| ((
          '!')  );$:=')'   ^(( (
          '}'   ))); $~=   '*'
          |((  '`')) ;(     $^
          )=(  '+')  ^+     ((
          ((   (     ((     ((
          ((    (    (      (
          ((     (  (       (
          (       '_'       )
          )      )) ))      )
         ))    ))))  )     ))
       ))))               ;#;#
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