$（printf'％q'“ $ {@：1}”）是否等于“ $ {*}”？

Question

Is $(printf '%q ' "${@:1}") equivalent to "${*}" ?

If they are, then, doing $(printf '%q ' "${@:2}") (note the 2 instead of 1 as before) is not possible with pure bash $* ?

Related questions:

1. POSIX sh equivalent for Bash's printf %q
2. How to use printf "%q " in bash?
3. Bash printf %q invalid directive
4. How to make runuser correctly forward all command line arguments, instead of trying to interpret them?
5. How to portability use "${@:2}"?

Answer 1

No, it is not equivalent, because words are splitted. Ex. the following code:

check_args() {
  echo "\$#=$#"
  printf "%s\n" "$@";
}

# setting arguments
set -- "space notspace" "newline"$'\n'"newline"
echo '1: ---------------- "$*"'
check_args "$*"

echo '2: ---------------- $(printf '\''%q '\'' "${@:1}")'
check_args $(printf '%q ' "${@:1}")

echo '3: ---------------- "$(printf '\''%q '\'' "${@:1}")"'
check_args "$(printf '%q ' "${@:1}")"

echo '4: ---------------- IFS=@ and "$*"'
( IFS=@; check_args "$*"; )

echo "5: ---------------- duplicating quoted"
check_args "$(printf '%s'"${IFS:0:1}" "${@:1}" | sed 's/'"${IFS:0:1}"'$//')"

echo "6: ---------------- duplicating quoted IFS=@"
( IFS=@; check_args "$(printf '%s'"${IFS:0:1}" "${@:1}" | sed 's/'"${IFS:0:1}"'$//')"; )

echo "7: ---------------- duplicating eval unquoted"
eval check_args $(printf '%q"'"${IFS:0:1}"'"' "${@:1}" | sed 's/'"${IFS:0:1}"'$//')

echo "8: ---------------- duplicating eval unquoted IFS=@"
( eval check_args $(IFS=@ ; printf '%q"'"${IFS:0:1}"'"' "${@:1}" | sed 's/"'"${IFS:0:1}"'"$//'); )

will output:

1: ---------------- "$*"
$#=1
space notspace newline
newline
2: ---------------- $(printf '%q ' "${@:1}")
$#=3
space\
notspace
$'newline\nnewline'
3: ---------------- "$(printf '%q ' "${@:1}")"
$#=1
space\ notspace $'newline\nnewline'
4: ---------------- IFS=@ and "$*"
$#=1
space notspace@newline
newline
5: ---------------- duplicating quoted
$#=1
space notspace newline
newline
6: ---------------- duplicating quoted IFS=@
$#=1
space notspace@newline
newline
7: ---------------- duplicating eval unquoted
$#=1
space notspace newline
newline
8: ---------------- duplicating eval unquoted IFS=@
$#=1
space notspace@newline
newline

tested on repl .

The "$*" outputs the arguments delimetered by IFS. So, shown in test 4 , if delimeter is not unset or set to space, then the output of $* will be delimetered by IFS, @ in this example.

Also when IFS is unset or set to space, the output of $* does not include a terminating space, while printf '%q ' will always print a trailing space on the end of the string.

The output of $(printf '%q ' "${@:1}") is still splitted on space. So the test case 2 receives 3 arguments, because the space notspace string is separated by space and splitted to two arguments. When enclosing the printf inside " will not help - printf substitutes ex. newlines for \\n characters.

Cases 5 , 6 , 7 , 8 are my tries to replicate the behavior of "$*" using printf. It can be seen with cases 7 and 8 I used eval , with cases 5 and 6 I quoted the command substitution. The output of cases ( 5 and 6 ) and ( 7 and 8 ) should match the output of cases 1 and 4 respectively.

For duplicating the behavior of "$*" special care needs to be taken for IFS to properly delimeter the strings. I used sed 's/'"${IFS:0:1}"'$//' to remove the trailing IFS separator from the printf output. The 5 and 6 cases are unquoted $(printf ...) tries, with 6 using IFS=@ to show the separating works. The 7 and 8 cases use eval with special handling on the IFS , cause the IFS character itself needs to be enclosed with quotes, so the shell will not split on it again, that's why printf '%q"'"${IFS:0:1}"'"' .

doing $(printf '%q ' "${@:2}") (note the 2 instead of 1 as before) is not possible with pure bash $*?

You probably could just shift the arguments inside the substitution $(shift; printf "%s\\n" "$*") , but as shown above, they are not equivalent anyway.

Answer 2

Using @Kamil Cuk answer as base, I built this new testing code for illustration, also available on repl :

#!/bin/bash
check_args() {
  echo "\$#=$#"
  local counter=0
  for var in "$@"
  do
      counter=$((counter+1));
      printf "$counter. '$var', ";
  done
  printf "\\n\\n"
}

# setting arguments
set -- "space notspace" "lastargument"; counter=1
echo $counter': ---------------- "$*"'; counter=$((counter+1))
check_args "$*"

echo $counter': ---------------- $*'; counter=$((counter+1))
check_args $*

echo $counter': ---------------- "$@"'; counter=$((counter+1))
check_args "$@"

echo $counter': ---------------- $@'; counter=$((counter+1))
check_args $@

echo $counter': ---------------- $(printf '\''%q '\'' "${@:1}")'; counter=$((counter+1))
check_args $(printf '%q ' "${@:1}")

echo $counter': ---------------- "$(printf '\''%q '\'' "${@:1}")"'; counter=$((counter+1))
check_args "$(printf '%q ' "${@:1}")"

echo $counter': ---------------- IFS=@ and "$*"'; counter=$((counter+1))
( IFS=@; check_args "$*"; )

echo "$counter: ---------------- duplicating quoted"; counter=$((counter+1))
check_args "$(printf '%s'"${IFS:0:1}" "${@:1}" | sed 's/'"${IFS:0:1}"'$//')"

echo "$counter: ---------------- duplicating quoted IFS=@"; counter=$((counter+1))
( IFS=@; check_args "$(printf '%s'"${IFS:0:1}" "${@:1}" | sed 's/'"${IFS:0:1}"'$//')"; )

echo "$counter: ---------------- duplicating eval unquoted"; counter=$((counter+1))
eval check_args $(printf '%q"'"${IFS:0:1}"'"' "${@:1}" | sed 's/'"${IFS:0:1}"'$//')

echo "$counter: ---------------- duplicating eval unquoted IFS=@"; counter=$((counter+1))
( eval check_args $(IFS=@ ; printf '%q"'"${IFS:0:1}"'"' "${@:1}" | sed 's/"'"${IFS:0:1}"'"$//'); )

-->

GNU bash, version 4.4.12(1)-release (x86_64-pc-linux-gnu)
1: ---------------- "$*"
$#=1
1. 'space notspace lastargument',

2: ---------------- $*
$#=3
1. 'space', 2. 'notspace', 3. 'lastargument',

3: ---------------- "$@"
$#=2
1. 'space notspace', 2. 'lastargument',

4: ---------------- $@
$#=3
1. 'space', 2. 'notspace', 3. 'lastargument',

5: ---------------- $(printf '%q ' "${@:1}")
$#=3
1. 'space', 2. 'notspace', 3. 'lastargument',

6: ---------------- "$(printf '%q ' "${@:1}")"
$#=1
1. 'space\ notspace lastargument ',

7: ---------------- IFS=@ and "$*"
$#=1
1. 'space notspace@lastargument',

8: ---------------- duplicating quoted
$#=1
1. 'space notspace lastargument',

9: ---------------- duplicating quoted IFS=@
$#=1
1. 'space notspace@lastargument',

10: ---------------- duplicating eval unquoted
$#=1
1. 'space notspace lastargument ',

11: ---------------- duplicating eval unquoted IFS=@
$#=1
1. 'space notspace@lastargument',