Note the difference between the following (assuming windows, adjust system as necessary).
perl -T -e "$ENV{PATH}='c:\\windows'; $string='original'; $string=$1 i
+f $ARGV[0] =~ /([a-zA-Z]+)/; system qq(notepad.exe $string) and die $
+!"
perl -T -e "$ENV{PATH}='c:\\windows'; $string='original'; $string=$1 i
+f $ARGV[0] =~ /([a-zA-Z]+)/; system qq(notepad.exe $string) and die $
+!" foo
perl -T -e "$ENV{PATH}='c:\\windows'; $string=$ARGV[0]; $string =~ s
+/ //g; system qq(notepad.exe $string) and die $
+!"
perl -T -e "$ENV{PATH}='c:\\windows'; $string=$ARGV[0]; $string =~ s
+/ //g; system qq(notepad.exe $string) and die $
+!" foo
Only the last command generates the error message: Insecure dependency in system while running with -T switch at -e line 1.. The first two commands illustrate how to untaint a parameter, the last two commands are doing what I think you describe.
