Added conditionals

manuscript/chapter19.txt

@@ -0,0 +1,190 @@
+# OTHER
+
+## Use `read` as an alternative to the `sleep` command
+
+Surprisingly, `sleep` is an external command and not a `bash` built-in.
+
+**CAVEAT:** Requires `bash` 4+
+
+**Example Function:**
+
+```sh
+read_sleep() {
+    # Usage: sleep 1
+    #        sleep 0.2
+    read -rst "${1:-1}" -N 999
+}
+```
+
+**Example Usage:**
+
+```shell
+read_sleep 1
+read_sleep 0.1
+read_sleep 30
+```
+
+## Check if a program is in the user's PATH
+
+```shell
+# There are 3 ways to do this and either one can be used.
+type -p executable_name &>/dev/null
+hash executable_name &>/dev/null
+command -v executable_name &>/dev/null
+
+# As a test.
+if type -p executable_name &>/dev/null; then
+    # Program is in PATH.
+fi
+
+# Inverse.
+if ! type -p executable_name &>/dev/null; then
+    # Program is not in PATH.
+fi
+
+# Example (Exit early if program is not installed).
+if ! type -p convert &>/dev/null; then
+    printf '%s\n' "error: convert is not installed, exiting..."
+    exit 1
+fi
+```
+
+## Get the current date using `strftime`
+
+Bash’s `printf` has a built-in method of getting the date which can be used in place of the `date` command.
+
+**CAVEAT:** Requires `bash` 4+
+
+**Example Function:**
+
+```sh
+date() {
+    # Usage: date "format"
+    # See: 'man strftime' for format.
+    printf "%($1)T\\n" "-1"
+}
+```
+
+**Example Usage:**
+
+```shell
+# Using above function.
+$ date "%a %d %b  - %l:%M %p"
+Fri 15 Jun  - 10:00 AM
+
+# Using printf directly.
+$ printf '%(%a %d %b  - %l:%M %p)T\n' "-1"
+Fri 15 Jun  - 10:00 AM
+
+# Assigning a variable using printf.
+$ printf -v date '%(%a %d %b  - %l:%M %p)T\n' '-1'
+$ printf '%s\n' "$date"
+Fri 15 Jun  - 10:00 AM
+```
+
+## Generate a UUID V4
+
+**Example Function:**
+
+```sh
+uuid() {
+    # Usage: uuid
+    C="89ab"
+
+    for ((N=0;N<16;++N)); do
+        B="$((RANDOM%256))"
+
+        case "$N" in
+            6)  printf '4%x' "$((B%16))" ;;
+            8)  printf '%c%x' "${C:$RANDOM%${#C}:1}" "$((B%16))" ;;
+
+            3|5|7|9)
+                printf '%02x-' "$B"
+            ;;
+
+            *)
+                printf '%02x' "$B"
+            ;;
+        esac
+    done
+
+    printf '\n'
+}
+```
+
+**Example Usage:**
+
+```shell
+$ uuid
+d5b6c731-1310-4c24-9fe3-55d556d44374
+```
+
+## Progress bars
+
+This is a simple way of drawing progress bars without needing a for loop
+in the function itself.
+
+**Example Function:**
+
+```sh
+bar() {
+    # Usage: bar 1 10
+    #            ^----- Elapsed Percentage (0-100).
+    #               ^-- Total length in chars.
+    ((elapsed=$1*$2/100))
+
+    # Create the bar with spaces.
+    printf -v prog  "%${elapsed}s"
+    printf -v total "%$(($2-elapsed))s"
+
+    printf '%s\r' "[${prog// /-}${total}]"
+}
+```
+
+**Example Usage:**
+
+```shell
+for ((i=0;i<=100;i++)); do
+    # Pure bash micro sleeps (for the example).
+    (:;:) && (:;:) && (:;:) && (:;:) && (:;:)
+
+    # Print the bar.
+    bar "$i" "10"
+done
+
+printf '\n'
+```
+
+## Get the list of functions in a script
+
+```sh
+get_functions() {
+    # Usage: get_functions
+    IFS=$'\n' read -d "" -ra functions < <(declare -F)
+    printf '%s\n' "${functions[@]//declare -f }"
+}
+```
+
+## Bypass shell aliases
+
+```shell
+# alias
+ls
+
+# command
+# shellcheck disable=SC1001
+\ls
+```
+
+## Bypass shell functions
+
+```shell
+# function
+ls
+
+# command
+command ls
+```
+
+<!-- CHAPTER END -->
+