Looping over arrays, printing both index and value

Question

You would find the array keys with "${!foo[@]}" (reference), so:

for i in "${!foo[@]}"; do 
  printf "%s\t%s\n" "$i" "${foo[$i]}"
done

Which means that indices will be in $i while the elements themselves have to be accessed via ${foo[$i]}

you can always use iteration param:

ITER=0
for I in ${FOO[@]}
do  
    echo ${I} ${ITER}
    ITER=$(expr $ITER + 1)
done

INDEX=0
for i in $list; do 
    echo ${INDEX}_$i
    let INDEX=${INDEX}+1
done

In bash 4, you can use associative arrays:

declare -A foo
foo[0]="bar"
foo[35]="baz"
for key in "${!foo[@]}"
do
    echo "key: $key, value: ${foo[$key]}"
done

# output
# $ key: 0, value bar.
# $ key: 35, value baz.

In bash 3, this works (also works in zsh):

map=( )
map+=("0:bar")
map+=("35:baz")

for keyvalue in "${map[@]}" ; do
    key=${keyvalue%%:*}
    value=${keyvalue#*:}
    echo "key: $key, value $value."
done

Simple one line trick for dumping array

I've added one value with spaces:

foo=()
foo[12]="bar"
foo[42]="foo bar baz"
foo[35]="baz"

I, for quickly dump bash arrays or associative arrays I use

This one line command:

paste <(printf "%s\n" "${!foo[@]}") <(printf "%s\n" "${foo[@]}")

Will render:

12  bar
35  baz
42  foo bar baz

Explained

• printf "%s\n" "${!foo[@]}" will print all keys separated by a newline,
• printf "%s\n" "${foo[@]}" will print all values separated by a newline,
• paste <(cmd1) <(cmd2) will merge output of cmd1 and cmd2 line by line.

Tunning

This could be tunned by -d switch:

paste -d : <(printf "%s\n" "${!foo[@]}") <(printf "%s\n" "${foo[@]}")
12:bar
35:baz
42:foo bar baz

or even:

paste -d = <(printf "foo[%s]\n" "${!foo[@]}") <(printf "'%s'\n" "${foo[@]}")
foo[12]='bar'
foo[35]='baz'
foo[42]='foo bar baz'

Associative array will work same:

declare -A bar=([foo]=snoopy [bar]=nice [baz]=cool [foo bar]='Hello world!')
paste -d = <(printf "bar[%s]\n" "${!bar[@]}") <(printf '"%s"\n' "${bar[@]}")
bar[foo bar]="Hello world!"
bar[foo]="snoopy"
bar[bar]="nice"
bar[baz]="cool"

Issue with newlines or special chars

Unfortunely, there is at least one condition making this not work anymore: when variable do contain newline:

foo[17]=$'There is one\nnewline'

Command paste will merge line-by-line, so output will become wrong:

paste -d = <(printf "foo[%s]\n" "${!foo[@]}") <(printf "'%s'\n" "${foo[@]}")
foo[12]='bar'
foo[17]='There is one
foo[35]=newline'
foo[42]='baz'
='foo bar baz'

For this work, you could use %q instead of %s in second printf command (and whipe quoting):

paste -d = <(printf "foo[%s]\n" "${!foo[@]}") <(printf "%q\n" "${foo[@]}")

Will render perfect:

foo[12]=bar
foo[17]=$'There is one\nnewline'
foo[35]=baz
foo[42]=foo\ bar\ baz

From man bash:

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

users=("kamal" "jamal" "rahim" "karim" "sadia")
index=()
t=-1

for i in ${users[@]}; do
  t=$(( t + 1 ))
  if [ $t -eq 0 ]; then
    for j in ${!users[@]}; do
      index[$j]=$j
    done
  fi
  echo "${index[$t]} is $i"
done