How to keep quotes in Bash arguments? [duplicate]

Solution 1:

using "$@" will substitute the arguments as a list, without re-splitting them on whitespace (they were split once when the shell script was invoked), which is generally exactly what you want if you just want to re-pass the arguments to another program.

Note that this is a special form and is only recognized as such if it appears exactly this way. If you add anything else in the quotes the result will get combined into a single argument.

What are you trying to do and in what way is it not working?

Solution 2:

There are two safe ways to do this:

1. Shell parameter expansion: ${variable@Q}:

When expanding a variable via ${variable@Q}:

The expansion is a string that is the value of parameter quoted in a format that can be reused as input.

Example:

$ expand-q() { for i; do echo ${i@Q}; done; }  # Same as for `i in "$@"`...
$ expand-q word "two words" 'new
> line' "single'quote" 'double"quote'
word
'two words'
$'new\nline'
'single'\''quote'
'double"quote'

2. printf %q "$quote-me"

printf supports quoting internally. The manual's entry for printf says:

%q Causes printf to output the corresponding argument in a format that can be reused as shell input.

Example:

$ cat test.sh 
#!/bin/bash
printf "%q\n" "$@"
$ 
$ ./test.sh this is "some test" 'new                                                                                                              
>line' "single'quote" 'double"quote'
this
is
some\ test
$'new\nline'
single\'quote
double\"quote
$

Note the 2nd way is a bit cleaner if displaying the quoted text to a human.

Related: For bash, POSIX sh and zsh: Quote string with single quotes rather than backslashes

Solution 3:

Yuku's answer only works if you're the only user of your script, while Dennis Williamson's is great if you're mainly interested in printing the strings, and expect them to have no quotes-in-quotes.

Here's a version that can be used if you want to pass all arguments as one big quoted-string argument to the -c parameter of bash or su:

#!/bin/bash
C=''
for i in "$@"; do 
    i="${i//\\/\\\\}"
    C="$C \"${i//\"/\\\"}\""
done
bash -c "$C"

So, all the arguments get a quote around them (harmless if it wasn't there before, for this purpose), but we also escape any escapes and then escape any quotes that were already in an argument (the syntax ${var//from/to} does global substring substitution).

You could of course only quote stuff which already had whitespace in it, but it won't matter here. One utility of a script like this is to be able to have a certain predefined set of environment variables (or, with su, to run stuff as a certain user, without that mess of double-quoting everything).

Update: I recently had reason to do this in a POSIX way with minimal forking, which lead to this script (the last printf there outputs the command line used to invoke the script, which you should be able to copy-paste in order to invoke it with equivalent arguments):

#!/bin/sh
C=''
for i in "$@"; do
    case "$i" in
        *\'*)
            i=`printf "%s" "$i" | sed "s/'/'\"'\"'/g"`
            ;;
        *) : ;;
    esac
    C="$C '$i'"
done
printf "$0%s\n" "$C"

I switched to '' since shells also interpret things like $ and !! in ""-quotes.