How to comment multi-line commands in shell scripts?

Question

When invoking long, switch-heavy commands, it's a good practice to write them in shell scripts. Is there an easy way to comment lines in such scripts? I've tried the following methods, but neither works.

# the \ is also commented out, resulting in "command" and "--good-switch".
command \
  #--bad-switch \
  --good-switch \

# seems to send an extra argument to the command
command \
  \ #--bad-switch \
  --good-switch

Answer 1

This might be an option: store the command and args in an array, then execute it after

# build the command
cmd=( ls
        -F
      # -a   # comment out this option temporarily
        -l
    )
# $cmd is now an array with 3 elements

# execute it
"${cmd[@]}"

Answer 2

I always moved the commented ones just after the command.

command \
  --good-switch
# --bad-switch          with explanation here, if needed

Answer 3

See the answer by Digital Ross.

See also the question I just posted, bash multi line command with comments after the continuation character.

This would be a useful feature. It is a pity it does not have standard support.

Answer 4

If you don't mind losing the value of the positional parameters, you can use them to build the command gradually. This also lets you use conditionals.

set -- command --first-option
# We need a special option on Tuesdays
if [ "$(date +%u)" = 2 ]; then
  set -- "$@" --tuesday
fi
set -- "$@" --last-option
# Finally we execute the command
"$@"

If you want to add options before the positional parameters, you might need to build the command backwards.

# We have a list of files in the positional parameters.
set -- --last-option "$@"
# We need a special option on Tuesdays
if [ "$(date +%u)" = 2 ]; then
  set -- --tuesday "$@"
fi
set -- command --first-option "$@"
# Finally we execute the command
"$@"

If you need to preserve the positional parameters, put this code in a function: the positional parameters are restored when the function returns.

Answer 5

a comment brakes the chain of conected lines, so the simplest solution would be to move the commented lines at the end of the list.

command \
  --good-switch \
  # --bad-switch \

If you don't want to change the order, you can use the : command (the colon utility, which does nothing) to keep the connected lines intact:

command \
  `: --bad-switch `\
  --good-switch \

---

I tested with this:

function command { 
  echo "num args:" $#;
}

Answer 6

The issue is that the slashes are removed before the line is parsed, so the first command is parsed as if you'd written command #--bad-switch --good-switch. If you have a really long sequence of commands, you could for example write a line-by-line comment block above or below it, explaining each in turn, or you could store the parameters in a variable (although that often gives quoting headaches with special characters).

Answer 7

$ echo abc `# comment` \
>      def `# comment 2` \
>      ghi
abc def ghi

$ echo abc `# comment` \
>      `#def # comment entire line` \
>      ghi
abc ghi

The backticks perform Command Substituion. This works because there is no standard output from executing a comment.