perl -e 'undef $/;
         $ENV{f}=$ARGV[0]; $_=`cat -- "\$f"`;
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Backquotes in scalar context already do what you want regardless of the contents of $/ and you can use $ARGV[0] directly instead of copying it to the environment, so that then becomes:

perl -e '
         $_=`cat -- "$ARGV[0]"`;
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You could also simplify that whole thing with the use of the -0 switch and the -p switch:

perl -0777pe's/^(\w+[^\n;]*?\([^\n;]*\n\{\n)[\s\S]+?\n(\}\n)/$1$2/mg' 
+FILE.c > FILE_MODIFIED.c
[download]