ff4b3db9cb
The syntax looks ugly, but this is the optimal way to do it. It doesn't have any extraneous output due to the parenthesis surrounding the command, and also sends error output to /dev/null.
202 lines
3.4 KiB
Plaintext
202 lines
3.4 KiB
Plaintext
# OTHER
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## Use `read` as an alternative to the `sleep` command
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Surprisingly, `sleep` is an external command and not a `bash` built-in.
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**CAVEAT:** Requires `bash` 4+
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**Example Function:**
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```sh
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read_sleep() {
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# Usage: sleep 1
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# sleep 0.2
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read -rst "${1:-1}" -N 999
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}
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```
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**Example Usage:**
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```shell
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read_sleep 1
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read_sleep 0.1
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read_sleep 30
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```
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## Check if a program is in the user's PATH
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```shell
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# There are 3 ways to do this and either one can be used.
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type -p executable_name &>/dev/null
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hash executable_name &>/dev/null
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command -v executable_name &>/dev/null
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# As a test.
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if type -p executable_name &>/dev/null; then
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# Program is in PATH.
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fi
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# Inverse.
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if ! type -p executable_name &>/dev/null; then
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# Program is not in PATH.
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fi
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# Example (Exit early if program is not installed).
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if ! type -p convert &>/dev/null; then
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printf '%s\n' "error: convert is not installed, exiting..."
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exit 1
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fi
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```
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## Get the current date using `strftime`
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Bash’s `printf` has a built-in method of getting the date which can be used in place of the `date` command.
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**CAVEAT:** Requires `bash` 4+
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**Example Function:**
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```sh
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date() {
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# Usage: date "format"
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# See: 'man strftime' for format.
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printf "%($1)T\\n" "-1"
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}
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```
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**Example Usage:**
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```shell
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# Using above function.
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$ date "%a %d %b - %l:%M %p"
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Fri 15 Jun - 10:00 AM
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# Using printf directly.
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$ printf '%(%a %d %b - %l:%M %p)T\n' "-1"
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Fri 15 Jun - 10:00 AM
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# Assigning a variable using printf.
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$ printf -v date '%(%a %d %b - %l:%M %p)T\n' '-1'
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$ printf '%s\n' "$date"
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Fri 15 Jun - 10:00 AM
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```
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## Generate a UUID V4
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**Example Function:**
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```sh
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uuid() {
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# Usage: uuid
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C="89ab"
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for ((N=0;N<16;++N)); do
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B="$((RANDOM%256))"
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case "$N" in
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6) printf '4%x' "$((B%16))" ;;
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8) printf '%c%x' "${C:$RANDOM%${#C}:1}" "$((B%16))" ;;
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3|5|7|9)
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printf '%02x-' "$B"
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;;
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*)
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printf '%02x' "$B"
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;;
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esac
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done
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printf '\n'
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}
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```
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**Example Usage:**
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```shell
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$ uuid
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d5b6c731-1310-4c24-9fe3-55d556d44374
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```
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## Progress bars
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This is a simple way of drawing progress bars without needing a for loop
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in the function itself.
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**Example Function:**
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```sh
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bar() {
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# Usage: bar 1 10
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# ^----- Elapsed Percentage (0-100).
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# ^-- Total length in chars.
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((elapsed=$1*$2/100))
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# Create the bar with spaces.
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printf -v prog "%${elapsed}s"
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printf -v total "%$(($2-elapsed))s"
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printf '%s\r' "[${prog// /-}${total}]"
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}
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```
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**Example Usage:**
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```shell
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for ((i=0;i<=100;i++)); do
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# Pure bash micro sleeps (for the example).
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(:;:) && (:;:) && (:;:) && (:;:) && (:;:)
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# Print the bar.
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bar "$i" "10"
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done
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printf '\n'
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```
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## Get the list of functions in a script
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```sh
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get_functions() {
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# Usage: get_functions
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IFS=$'\n' read -d "" -ra functions < <(declare -F)
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printf '%s\n' "${functions[@]//declare -f }"
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}
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```
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## Bypass shell aliases
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```shell
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# alias
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ls
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# command
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# shellcheck disable=SC1001
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\ls
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```
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## Bypass shell functions
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```shell
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# function
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ls
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# command
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command ls
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```
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## Run a command in the background
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This will run the given command and keep it running even after the terminal is closed.
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```sh
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bkr() {
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(nohup "$@" &>/dev/null &)
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}
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bkr ./some_script.sh # some_script.sh is now running in the background
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```
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<!-- CHAPTER END -->
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