#!/usr/bin/env rc

fn f {

n=$1

if(! cat $f | cut -c1-$n | 9 grep -v '^[  ]+$' >/dev/null){

x=`{f `{expr $n + 1}}

echo '.'$"x

}

}

f=/tmp/com.$pid

cat >$f

switch($%){

case *.go *.c

c='//'

case *

c='#'

}

# Remove comment?

if(cat $f | 9 grep '^[  ]*'$c' ' >/dev/null){

cat $f | 9 sed 's|'$c' ||'

exit

}

# Add comment.

s=`{f 1}

if(~ $#s 0)

cat $f | 9 sed 's|^|'$c' |'

if not

cat $f | 9 sed 's|^('$"s')|\1'$c' |'

rm $f

I name this |com. The original motivation was to avoid manual keying in of the comment characters, which I found myself doing quite frequently for short line ranges.

It also works well with Go's "imported and not used" error. Once plumbed to the offending import line, it only takes one click to temporarily disable an import.