How to conditionally add elements to an array in shell script

Question

In the below shell script, I'm trying to conditionally add elements to an array which is syntactically incorrect when checked in shellcheck.

#!/bin/bash

echo "Hello World";
HH=1

ARR=(
    "a"
    "b"
    "c"
    if [ ${HH} = 1 ]; then
        "f"
    else
        "g"
    fi
    "d"
    "e"
)

for arr in "${ARR[@]}"; do
    echo "${arr}"
done

ShellCheck Error:

Line 6:
ARR=(
^-- SC1009 (info): The mentioned syntax error was in this variable assignment.
    ^-- SC1073 (error): Couldn't parse this array assignment. Fix to allow more checks.
 
Line 12:
    if [ ${HH} = 1 ]; then
                    ^-- SC1072 (error): Expected ) to close array assignment. Fix any mentioned problems and try again.

Ed Morton · Accepted Answer · 2025-10-15 17:35:04Z

4

Keep it simple and set a variable to the value you want to use in the array:

if [[ "$HH" == 1 ]]; then
    foo="f"
else
    foo="g"
fi

ARR=(
    "a"
    "b"
    "c"
    "$foo"
    "d"
    "e"
)

answered Oct 15 at 17:35

Ed Morton

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3 Comments

Charles Duffy Oct 15 at 19:31

It's worth noting that this is much more efficient than the subshell in the other answer's first example (which forks off a subprocess to run the if)

Harry Oct 31 at 7:03

What if there is no else part? I mean add element to the array only if HH=1, otherwise don't

Ed Morton Oct 31 at 12:20

@Harry Chameleon Questions are strongly discouraged on this forum, just ask a new question if you have new requirements after people have posted answers to the question you asked.

KamilCuk · Accepted Answer · 2025-10-31 09:46:49Z

2

How to conditionally add elements to an array in shell script

Here are some examples:

HH=1
ARR=(
    "a"
    "b"
    "c"
    "$(if [[ ${HH} == 1 ]]; then echo f; else echo g; fi)"
    "d"
    "e"
)

HH=1
lookup=([0]=g [1]=f)
ARR=(
    "a"
    "b"
    "c"
    "${lookup[HH]}"
    "d"
    "e"
)

HH=1
ARR=(
    "a"
    "b"
    "c"
    "d"
    "e"
)
if [[ ${HH} == 1 ]]; then
   ARR+=(f)
else
   ARR+=(g)
if

# insert element $3 at position $2 in array $1
array_insert() {
    local -n _arr="$1" || return 2
    _arr=("${_arr[@]::$2}" "${@:3}" "${_arr[@]:$2}")
}
HH=1
ARR=(
    "a"
    "b"
    "c"
    "d"
    "e"
)
if [[ ${HH} == 1 ]]; then
   array_insert ARR 3 f
else
   array_insert ARR 3 g
if

HH=1
ARR=(
    "a"
    "b"
    "c"
)
if [[ ${HH} == 1 ]]; then
   ARR+=("f")
else
   ARR+=("g")
if
ARR+=(
    "d"
    "e"
)

In case there is only if part the array contains an empty string element. How do I fix that? For e.g; "$(if [ "${HH}" = 1 ]; then echo "d"; fi)", this adds an empty string element to the array if HH=0

If you are fine with ignoring shellcheck error https://www.shellcheck.net/wiki/SC2046 , then remove the quotes around the $(..) expression. Unquoted command substition will result in executing word splitting (and filename expansion) over the result, effectively replacing an empty string with no words resulting in no items. However this might not work with a string with spaces, * ? [ characters in the resulting string. In such cases, use other presented method. See also https://mywiki.wooledge.org/WordSplitting , https://www.gnu.org/software/bash/manual/html_node/Shell-Expansions.html .

HH=1
ARR=(
    "a"
    "b"
    "c"
    $(if [[ ${HH} == 1 ]]; then echo f; fi)
    "d"
    "e"
    # pitfalls:
    $(if [[ ${HH} == 1 ]]; then echo "a b c"; fi)  # adds 3 elements
    $(if [[ ${HH} == 1 ]]; then echo "'a b c'"; fi)  # also adds 3 elements, it is just not possible to quote "inside"
    $(if [[ ${HH} == 1 ]]; then echo "*"; fi)  # expands *, adds all files in PWD
)

There is no need to do if [ ! ${#ARR[@]} -eq 0 ]; then. When array is empty, "${ARR[@]}" is nothing, so the loop will not run at all.

edited Oct 31 at 9:46

answered Oct 15 at 8:44

KamilCuk

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5 Comments

Philippe Oct 16 at 20:00

Why not use lookup=(g f) instead of lookup=([0]=g [1]=f)

KamilCuk Oct 16 at 20:27

There is no reason.

Harry Oct 31 at 6:53

In case there is only if part the array contains an empty string element. How do I fix that? For e.g; "$(if [ "${HH}" = 1 ]; then echo "d"; fi)", this adds an empty string element to the array if HH=0

KamilCuk Oct 31 at 9:43

If you are fine with ignoring shellcheck warning, then remove the quotes from the expression. Unquoted command substition will result in executing word splitting (and filename expansion) over the result, effectively replacing an empty string with no words resulting in no items. So just $(if [ "${HH}" = 1 ]; then echo "d"; fi). However it might not work with a string with spaces, * ? [ characters in the d string. In such cases, use other presented method.

KamilCuk Oct 31 at 9:50

I adited the answer and added this.

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