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Strings

Strip pattern from start of string

lstrip() {
    # Usage: lstrip "string" "pattern"
    printf '%s\n' "${1##$2}"
}

Example Usage:

$ lstrip "The Quick Brown Fox" "The "
Quick Brown Fox

Strip pattern from end of string

rstrip() {
    # Usage: rstrip "string" "pattern"
    printf '%s\n' "${1%%$2}"
}

Example Usage:

$ rstrip "The Quick Brown Fox" " Fox"
The Quick Brown

Trim leading and trailing white-space from string

This is an alternative to sed, awk, perl and other tools. The

function below works by finding all leading and trailing white-space and

removing it from the start and end of the string.

trim_string() {
    # Usage: trim_string "   example   string    "

    # Remove all leading white-space.
    # '${1%%[![:space:]]*}': Strip everything but leading white-space.
    # '${1#${XXX}}': Remove the white-space from the start of the string.
    trim=${1#${1%%[![:space:]]*}}

    # Remove all trailing white-space.
    # '${trim##*[![:space:]]}': Strip everything but trailing white-space.
    # '${trim#${XXX}}': Remove the white-space from the end of the string.
    trim=${trim%${trim##*[![:space:]]}}

    printf '%s\n' "$trim"
}

Example Usage:

$ trim_string "    Hello,  World    "
Hello,  World

$ name="   John Black  "
$ trim_string "$name"
John Black

Trim all white-space from string and truncate spaces

This is an alternative to sed, awk, perl and other tools. The function below works by abusing word splitting to create a new string without leading/trailing white-space and with truncated spaces.

# shellcheck disable=SC2086,SC2048
trim_all() {
    # Usage: trim_all "   example   string    "

    # Disable globbing to make the word-splitting below safe.
    set -f

    # Set the argument list to the word-splitted string.
    # This removes all leading/trailing white-space and reduces
    # all instances of multiple spaces to a single ("  " -> " ").
    set -- $*

    # Print the argument list as a string.
    printf '%s\n' "$*"

    # Re-enable globbing.
    set +f
}

Example Usage:

$ trim_all "    Hello,    World    "
Hello, World

$ name="   John   Black  is     my    name.    "
$ trim_all "$name"
John Black is my name.

Check if string contains a sub-string

case $var in
    *sub_string1*)
        # Do stuff
    ;;

    *sub_string2*)
        # Do other stuff
    ;;

    *)
        # Else
    ;;
esac

Check if string starts with sub-string

case $var in
    sub_string1*)
        # Do stuff
    ;;

    sub_string2*)
        # Do other stuff
    ;;

    *)
        # Else
    ;;
esac

Check if string ends with sub-string

case $var in
    *sub_string1)
        # Do stuff
    ;;

    *sub_string2)
        # Do other stuff
    ;;

    *)
        # Else
    ;;
esac

Split a string on a delimiter

This is an alternative to cut, awk and other tools.

split() {
    # Disable globbing.
    # This ensures that the word-splitting is safe.
    set -f

    # Store the current value of 'IFS' so we
    # can restore it later.
    old_ifs=$IFS

    # Change the field separator to what we're
    # splitting on.
    IFS=$2

    # Create an argument list splitting at each
    # occurance of '$2'.
    #
    # This is safe to disable as it just warns against
    # word-splitting which is the behavior we expect.
    # shellcheck disable=2086
    set -- $1

    # Print each list value on its own line.
    printf '%s\n' "$@"

    # Restore the value of 'IFS'.
    IFS=$old_ifs

    # Re-enable globbing.
    set +f
}

Example Usage:

$ split "apples,oranges,pears,grapes" ","
apples
oranges
pears
grapes

$ split "1, 2, 3, 4, 5" ", "
1
2
3
4
5

Trim quotes from a string

trim_quotes() {
    # Usage: trim_quotes "string"

    # Disable globbing.
    # This makes the word-splitting below safe.
    set -f

    # Store the current value of 'IFS' so we
    # can restore it later.
    old_ifs=$IFS

    # Set 'IFS' to ["'].
    IFS=\"\'

    # Create an argument list, splitting the
    # string at ["'].
    #
    # Disable this shellcheck error as it only
    # warns about word-splitting which we expect.
    # shellcheck disable=2086
    set -- $1

    # Set 'IFS' to blank to remove spaces left
    # by the removal of ["'].
    IFS=

    # Print the quote-less string.
    printf '%s\n' "$*"

    # Restore the value of 'IFS'.
    IFS=$old_ifs

    # Re-enable globbing.
    set +f
}

Example Usage:

$ var="'Hello', \"World\""
$ trim_quotes "$var"
Hello, World