Printing command line arguments in quoted form

December 30, 2021

$@ when double quoted("$@") expands to "$1" "$2" "$3" …

There seems to be no easy way to print quoted form of what is inside "$@"

$ set -- "one two" three  
$ echo "$@"
one two three

What I am looking for is, output of

'one two' three

Using ‘set -x’, does echo quoted form of arguments inside "$@"

$ set -x; echo "$@"; set +x
+ set -x
+ echo 'one two' three
one two three
+ set +x

User defined variable $DOLLAR_AT contains same things inside it, as what
"$@" contains

$ DOLLAR_AT="'one two' three"

Dumping out, what is inside $DOLLAR_AT, using ‘echo’ works as expected

$ echo $DOLLAR_AT
'one two' three

due to some kind of automatic quoting by the shell of arguments that contain special characters

$ set -x; echo $DOLLAR_AT; set +x
+ echo ''\''one' 'two'\''' three
+ set +x

It is not clear why

$ echo "$@"

does not produce same output as

$ echo "$DOLLAR_AT"

When starting a command from a shell script using received "$@", there is a
need to print out what is inside "$@" in a quoted form before invoking the
command.

There is a similar need in printing out command line arguments passed from
a bash array.

$ CMDARGS=("one two" "three")

Evaluating the array within double quotes does not print array elements in a quoted form

$ echo "${CMDARGS[@]}"
one two three

I also need a compact way to print what is in $CMDARGS[@] in a quoted
form similar to what comes out of this iteration

$ for ARG in "${CMDARGS[@]}"; do echo \'$ARG\'; done
'one two'
'three'

>Solution :

You could try inline:

$ set -- 'foo bar' baz
$ echo ${@@Q}
'Foo bar' 'baz'

$ echo ${@@A}
set -- 'Foo bar' 'baz'

$ DOLLAR_AT="'one two' three"
$ echo ${DOLLAR_AT@Q}
''\''one two'\'' three'

$ echo ${DOLLAR_AT@A}
DOLLAR_AT=''\''one two'\'' three'

More info in bash’s manpage, under Parameter Expansion subsection.

   ${parameter@operator}
         Parameter transformation.  The expansion is either a transforma‐
         tion  of  the  value of parameter or information about parameter
         itself, depending on the value of operator.  Each operator is  a
         single letter:
 ...
         Q      The  expansion is a string that is the value of parameter
                quoted in a format that can be reused as input.
 ...
         A      The expansion is a string in the form  of  an  assignment
                statement  or  declare  command  that, if evaluated, will
                recreate parameter with its attributes and value.