Added introduction.
This commit is contained in:
Dylan Araps
@@ -1,130 +1,376 @@
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# Arrays
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# Strings
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## Reverse an array
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## Trim leading and trailing white-space from string
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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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This is an alternative to `sed`, `awk`, `perl` and other tools. The
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function below works by finding all leading and trailing white-space and
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removing it from the start and end of the string. The `:` built-in is used in place of a temporary variable.
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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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trim_string() {
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# Usage: trim_string " example string "
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: "${1#"${1%%[![:space:]]*}"}"
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: "${_%"${_##*[![:space:]]}"}"
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printf '%s\n' "$_"
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}
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```
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**Example Usage:**
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```shell
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$ 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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$ trim_string " Hello, World "
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Hello, World
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$ arr=(red blue green)
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$ reverse_array "${arr[@]}"
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green
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blue
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red
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$ name=" John Black "
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$ trim_string "$name"
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John Black
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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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## Trim all white-space from string and truncate spaces
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This is an alternative to `sed`, `awk`, `perl` and other tools. The
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function below works by abusing word splitting to create a new string
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without leading/trailing white-space and with truncated spaces.
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**Example Function:**
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```sh
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# shellcheck disable=SC2086,SC2048
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trim_all() {
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# Usage: trim_all " example string "
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set -f
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set -- $*
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printf '%s\n' "$*"
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set +f
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}
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```
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**Example Usage:**
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```shell
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$ trim_all " Hello, World "
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Hello, World
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$ name=" John Black is my name. "
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$ trim_all "$name"
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John Black is my name.
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```
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## Use regex on a string
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We can use the result of `bash`'s regex matching to replace `sed` for a
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large number of use-cases.
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**CAVEAT**: This is one of the few platform dependant `bash` features.
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`bash` will use whatever regex engine is installed on the user's system.
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Stick to POSIX regex features if aiming for compatibility.
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**CAVEAT**: This example only prints the first matching group. When using
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multiple capture groups some modification is needed.
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**Example Function:**
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```sh
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regex() {
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# Usage: regex "string" "regex"
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[[ $1 =~ $2 ]] && printf '%s\n' "${BASH_REMATCH[1]}"
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}
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```
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**Example Usage:**
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```shell
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$ # Trim leading white-space.
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$ regex ' hello' '^\s*(.*)'
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hello
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$ # Validate a hex color.
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$ regex "#FFFFFF" '^(#?([a-fA-F0-9]{6}|[a-fA-F0-9]{3}))$'
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#FFFFFF
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$ # Validate a hex color (invalid).
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$ regex "red" '^(#?([a-fA-F0-9]{6}|[a-fA-F0-9]{3}))$'
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# no output (invalid)
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```
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**Example Usage in script:**
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```shell
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is_hex_color() {
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if [[ "$1" =~ ^(#?([a-fA-F0-9]{6}|[a-fA-F0-9]{3}))$ ]]; then
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printf '%s\n' "${BASH_REMATCH[1]}"
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else
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printf '%s\n' "error: $1 is an invalid color."
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return 1
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fi
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}
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read -r color
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is_hex_color "$color" || color="#FFFFFF"
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# Do stuff.
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```
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## Split a string on a delimiter
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This is an alternative to `cut`, `awk` and other tools.
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**Example Function:**
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```sh
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split() {
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# Usage: split "string" "delimiter"
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IFS=$'\n' read -d "" -ra arr <<< "${1//$2/$'\n'}"
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printf '%s\n' "${arr[@]}"
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}
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```
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**Example Usage:**
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```shell
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$ split "apples,oranges,pears,grapes" ","
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apples
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oranges
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pears
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grapes
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$ split "1, 2, 3, 4, 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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# Multi char delimiters work too!
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$ split "hello---world---my---name---is---john" "---"
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hello
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world
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my
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name
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is
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john
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```
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## Change a string to lowercase
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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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lower() {
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# Usage: lower "string"
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printf '%s\n' "${1,,}"
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}
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```
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**Example Usage:**
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```shell
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$ 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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$ lower "HELLO"
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hello
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$ arr=(red red green blue blue)
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$ remove_array_dups "${arr[@]}"
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red
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green
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blue
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$ lower "HeLlO"
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hello
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$ lower "hello"
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hello
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```
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## Random array element
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## Change a string to uppercase
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**CAVEAT:** Requires `bash` 4+
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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 % $#]}"
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upper() {
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# Usage: upper "string"
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printf '%s\n' "${1^^}"
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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 "${array[@]}"
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yellow
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$ upper "hello"
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HELLO
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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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$ upper "HeLlO"
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HELLO
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$ upper "HELLO"
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HELLO
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```
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## Cycle through an array
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## Trim quotes from a string
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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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**Example Function:**
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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>=${#arr[@]}-1?0:++i))
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trim_quotes() {
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# Usage: trim_quotes "string"
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: "${1//\'}"
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printf '%s\n' "${_//\"}"
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}
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```
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**Example Usage:**
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## Toggle between two values
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```shell
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$ var="'Hello', \"World\""
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$ trim_quotes "$var"
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Hello, World
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```
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This works the same as above, this is just a different use case.
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## Strip all instances of pattern from string
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**Example Function:**
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```sh
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arr=(true false)
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cycle() {
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printf '%s ' "${arr[${i:=0}]}"
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((i=i>=${#arr[@]}-1?0:++i))
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strip_all() {
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# Usage: strip_all "string" "pattern"
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printf '%s\n' "${1//$2}"
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}
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```
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**Example Usage:**
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```shell
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$ strip_all "The Quick Brown Fox" "[aeiou]"
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Th Qck Brwn Fx
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$ strip_all "The Quick Brown Fox" "[[:space:]]"
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TheQuickBrownFox
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$ strip_all "The Quick Brown Fox" "Quick "
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The Brown Fox
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```
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## Strip first occurrence of pattern from string
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**Example Function:**
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```sh
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strip() {
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# Usage: strip "string" "pattern"
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printf '%s\n' "${1/$2}"
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}
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```
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**Example Usage:**
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```shell
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$ strip "The Quick Brown Fox" "[aeiou]"
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Th Quick Brown Fox
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$ strip "The Quick Brown Fox" "[[:space:]]"
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TheQuick Brown Fox
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```
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## Strip pattern from start of string
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**Example Function:**
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```sh
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lstrip() {
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# Usage: lstrip "string" "pattern"
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printf '%s\n' "${1##$2}"
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}
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```
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**Example Usage:**
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```shell
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$ lstrip "The Quick Brown Fox" "The "
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Quick Brown Fox
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```
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## Strip pattern from end of string
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**Example Function:**
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```sh
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rstrip() {
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# Usage: rstrip "string" "pattern"
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printf '%s\n' "${1%%$2}"
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}
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```
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**Example Usage:**
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```shell
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$ rstrip "The Quick Brown Fox" " Fox"
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The Quick Brown
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```
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## Check if string contains a sub-string
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**Using a test:**
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```shell
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if [[ "$var" == *sub_string* ]]; then
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printf '%s\n' "sub_string is in var."
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fi
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# Inverse (substring not in string).
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if [[ "$var" != *sub_string* ]]; then
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printf '%s\n' "sub_string is not in var."
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fi
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# This works for arrays too!
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if [[ "${arr[*]}" == *sub_string* ]]; then
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printf '%s\n' "sub_string is in array."
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fi
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```
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**Using a case statement:**
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```shell
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case "$var" in
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*sub_string*)
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# Do stuff
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;;
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*sub_string2*)
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# Do more stuff
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;;
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*)
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# Else
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;;
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esac
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```
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## Check if string starts with sub-string
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```shell
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if [[ "$var" == sub_string* ]]; then
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printf '%s\n' "var starts with sub_string."
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fi
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# Inverse (var doesn't start with sub_string).
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if [[ "$var" != sub_string* ]]; then
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printf '%s\n' "var does not start with sub_string."
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fi
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```
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## Check if string ends with sub-string
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```shell
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if [[ "$var" == *sub_string ]]; then
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printf '%s\n' "var ends with sub_string."
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fi
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# Inverse (var doesn't start with sub_string).
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if [[ "$var" != *sub_string ]]; then
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printf '%s\n' "var does not end with sub_string."
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fi
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```
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<!-- CHAPTER END -->
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Reference in New Issue
Block a user