How to preserve double quotes in $@ in a shell scr

问题:

Let's say I have a really simple shell script 'foo':

  #!/bin/sh
  echo $@

If I invoke it like so:

  foo 1 2 3

It happily prints:

  1 2 3

However, let's say one of my arguments is double-quote enclosed and contains whitespace:

  foo 1 "this arg has whitespace" 3

foo happily prints:

  1 this arg has whitespace 3

The double-quotes have been stripped! I know shell thinks its doing me a favor, but... I would like to get at the original version of the arguments, unmolested by shell's interpretation. Is there any way to do so?

回答1:

First, you probably want quoted version of $@, i.e. "$@". To feel the difference, try putting more than one space inside the string.

Second, quotes are element of shell's syntax -- it doesn't do you a favor. To preserve them, you need to escape them. Examples:

foo 1 "\"this arg has whitespace\"" 3

foo 1 '"this arg has whitespace"' 3

回答2:

Double quote $@:

#!/bin/sh
for ARG in "$@"
do
    echo $ARG
done

Then:

foo 1 "this arg has whitespace" 3

will give you:

1
this arg has whitespace
3

回答3:

What i'd do is to quote all the arguments received with spaces that might help your case.

for x in "${@}" ; do
    # try to figure out if quoting was required for the $x
    if [[ "$x" != "${x%[[:space:]]*}" ]]; then
        x="\""$x"\""
    fi
    echo $x
    _args=$_args" "$x
done

echo "All Cmd Args are: $_args"

回答4:

Let's suppose you are in a more rigid set-up and you CANNOT change your command line, and make it more "friendly" by escaping the double quotes. For example:

example_script.sh argument_without_quotes "argument with quotes i cannot escape"

First consider that inside your script you can't tell if an argument is passed with or without quotes, because the shell strips them.

So what you can possibly do is rebuilding double quotes for arguments containing whitespaces

This example rebuilds the whole command line, double-quoting arguments that have white spaces

#!/bin/sh
#initialize the variable that will contain the whole argument string
argList=""
#iterate on each argument
for arg in "$@"
do
  #if an argument contains a white space, enclose it in double quotes and append to the list
  #otherwise simply append the argument to the list
  if echo $arg | grep -q " "; then
   argList="$argList \"$arg\""
  else
   argList="$argList $arg"
  fi
done

#remove a possible trailing space at the beginning of the list
argList=$(echo $argList | sed 's/^ *//')

#pass your argument list WITH QUOTES
echo "my_executable" $argList
#my_executable $argList

Note this limitation. If you run this example

example_script.sh "argument with spaces" argument_without_spaces "argument_doublequoted_but_without_spaces"

you will get this output

my_executable "argument with spaces" argument_without_spaces argument_doublequoted_but_without_spaces

Note the last argument: since it had no spaces, it has not been enclosed again in double quotes, but this shouldn't be an issue.

回答5:

You need to quote the quotes:

foo 1 "\"this arg has whitespace\"" 3

or (more simply)

foo 1 '"this arg has whitespace"' 3

You need to quote the double quotes to make sure that the shell doesn't remove them when parsing word arguments.