Bash add array string suffix to an array

Question

I have two bash arrays, and I want to append array strings to the end of the name array elements.

array=(a b c)
name=(toto_ tata_)

result :

toto_a
toto_b
toto_c
tata_a
tata_b
tata_c

I tried those command :

for i in "${name[@]}"
do
    arra=( "${i/%/$array[@]}" )
done
printf '%s\n' "${arra[@]}"

glenn jackman · Accepted Answer · 2021-12-03 14:44:20Z

2

Using Brace Expansion to expand as a cross-product

readarray -t new_array < <(IFS=,; eval "printf '%s\n' {${name[*]}}{${array[*]}}")
# ....................................................^..........^^...........^

then

$ declare -p new_array
declare -a new_array=([0]="toto_a" [1]="toto_b" [2]="toto_c" [3]="tata_a" [4]="tata_b" [5]="tata_c")

Eval is necessary to allow the variable expansion to occur first, then perform the brace expansion second.

answered Dec 3, 2021 at 14:44

glenn jackman

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3 Comments

F. Hauri - Give Up GitHub Over a year ago

Or just: (IFS=,; eval "printf '%s\n' {${name[*]}}{${array[*]}}")... Nice, but not easy to debug! I don't like to play with $IFS... but here, it's fun ;-)

F. Hauri - Give Up GitHub Over a year ago

Or even, moving eval at begin of line: . <(IFS=,;echo $'printf "%s\\n"' "{${name[*]}}{${array[*]}}")

M. Nejat Aydin Over a year ago

Nice but this will fail to work properly if an array element contains a ,. Also it must be noted that array elements will be subject to eval too (Assume name=(toto_ tata_ '$(some_command)'), then some_command will be executed by eval!). So array elements must be sanitized if they come from an external source.

0stone0 · Accepted Answer · 2021-12-03 12:39:00Z

1

I'd recommend using a second for:

array=(a b c)
name=(toto_ tata_)
arra=()

for i in "${name[@]}"; do
    for j in "${array[@]}"; do
        arra+=("$i$j")
    done
done
printf '%s\n' "${arra[@]}"

Will produce:

toto_a
toto_b
toto_c
tata_a
tata_b
tata_c

Try it online!

answered Dec 3, 2021 at 12:39

0stone0

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1 Comment

F. Hauri - Give Up GitHub Over a year ago

This could by done without for loop!

F. Hauri - Give Up GitHub · Accepted Answer · 2021-12-03 13:37:51Z

1

Second `for` could be avoided by Parameter expansion

for nam in "${name[@]}";do printf "${nam/%/%s\\n}" "${array[@]}";done

will produce:

toto_a
toto_b
toto_c
tata_a
tata_b
tata_c

For fun, some variants (without any `for` loop):

printf -v fmt "${name[*]/%/%%s\\n}"
printf "${fmt// }" ${array[@]}
toto_a
tata_b
toto_c
tata_

or

printf -v fmt "${name[*]/%/%%s\\n}";printf "${fmt// }" ${array[@]}{,}
toto_a
tata_b
toto_c
tata_a
toto_b
tata_c

then without for, but with a fork to sort

printf -v fmt "${name[*]/%/%%s\\n}";printf "${fmt// }" ${array[@]}{,} |
    sort -k 1r,1.5
toto_a
toto_b
toto_c
tata_a
tata_b
tata_c

edited Dec 3, 2021 at 13:37

answered Dec 3, 2021 at 13:14

F. Hauri - Give Up GitHub

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Second `for` could be avoided by Parameter expansion

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Second for could be avoided by Parameter expansion

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Second `for` could be avoided by Parameter expansion

For fun, some variants (without any `for` loop):