CODEWITHSUNDEEP
arraysbashvariablesexpansion
Thomas_SO
Thomas_SO

Reputation: 2581

Bash-Scripting: what does ${VARIABLE[number]} mean if VARIABLE is not an array?

I know that there are arrays in bash-scripting. For example:

JOBS=("JOB1", "JOB2", "JOB3")

Then one can refer to, say, JOB2 as follows:

${JOBS[1]}

In a bash script I recently encountered a normal (non-array) variable:

JOB="XYZ"

Later in the script, this variable was referred to as follows:

${JOB[0]}

and:

${JOB[1]}

Since JOB is not an array, I do not understand what ${JOB[number]} is expanded to.

Is this just a programming mistake? Or is there some construct regarding normal variables I am not aware of?

Upvotes: 0

Views: 73

Answers (2)

AYSHANI MALIK
AYSHANI MALIK

Reputation: 1

I believe newer versions of Bash support one-dimensional arrays and the syntax can be seen in the following link as follows : Advanced Bash-Scripting Guide

If Variable is not an array, ${Variable[Number]} will work only for Number=0 but not for any other number as ${Variable[0]} and $Variable - both are same.

Upvotes: 0

chepner
chepner

Reputation: 532268

bash doesn't have array values at all; it provides array syntax to use with names that have an array attribute set:

$ a=()
$ declare -p a
declare -a a=()

The -a in the output indicates that the array attribute is set on a, having been set implicitly by the preceding array assignment.

For such variables, the name-plus-index acts as a sort of "virtual" name, and like any other name, expands to the empty string if the name doesn't actually exist, as is the case with ${JOB[1]}. A side effect of the implementation is the $foo and ${foo[0]} are generally equivalent, whether or not foo has its array attribute set.

Upvotes: 3

Related Questions