131 lines
2.0 KiB
Plaintext
131 lines
2.0 KiB
Plaintext
# Arrays
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## Reverse an array
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Enabling `extdebug` allows access to the `BASH_ARGV` array which stores
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the current function’s arguments in reverse.
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**Example Function:**
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```sh
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reverse_array() {
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# Usage: reverse_array "array"
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shopt -s extdebug
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f()(printf '%s\n' "${BASH_ARGV[@]}"); f "$@"
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shopt -u extdebug
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}
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```
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**Example Usage:**
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```shell
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$ reverse_array 1 2 3 4 5
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5
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4
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3
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2
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1
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$ arr=(red blue green)
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$ reverse_array "${arr[@]}"
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green
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blue
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red
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```
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## Remove duplicate array elements
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Create a temporary associative array. When setting associative array
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values and a duplicate assignment occurs, bash overwrites the key. This
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allows us to effectively remove array duplicates.
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**CAVEAT:** Requires `bash` 4+
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**Example Function:**
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```sh
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remove_array_dups() {
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# Usage: remove_array_dups "array"
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declare -A tmp_array
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for i in "$@"; do
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[[ "$i" ]] && IFS=" " tmp_array["${i:- }"]=1
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done
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printf '%s\n' "${!tmp_array[@]}"
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}
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```
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**Example Usage:**
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```shell
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$ remove_array_dups 1 1 2 2 3 3 3 3 3 4 4 4 4 4 5 5 5 5 5 5
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1
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2
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3
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4
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5
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$ arr=(red red green blue blue)
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$ remove_array_dups "${arr[@]}"
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red
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green
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blue
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```
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## Random array element
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**Example Function:**
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```sh
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random_array_element() {
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# Usage: random_array_element "array"
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local arr=("$@")
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printf '%s\n' "${arr[RANDOM % $#]}"
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}
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```
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**Example Usage:**
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```shell
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$ array=(red green blue yellow brown)
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$ random_array_element "${array[@]}"
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yellow
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# You can also just pass multiple arguments.
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$ random_array_element 1 2 3 4 5 6 7
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3
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```
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## Cycle through an array
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Each time the `printf` is called, the next array element is printed. When
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the print hits the last array element it starts from the first element
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again.
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```sh
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arr=(a b c d)
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cycle() {
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printf '%s ' "${arr[${i:=0}]}"
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((i=i>=${#arr[@]}-1?0:++i))
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}
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```
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## Toggle between two values
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This works the same as above, this is just a different use case.
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```sh
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arr=(true false)
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cycle() {
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printf '%s ' "${arr[${i:=0}]}"
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((i=i>=${#arr[@]}-1?0:++i))
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}
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```
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<!-- CHAPTER END -->
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