Pure Sh Bible

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

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

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

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

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 '%sn' "$trim"
}

$ trim_string "    Hello,  World    "
Hello,  World

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

# Print the argument list as a string.
printf ‘%sn’ “$*”

# Re-enable globbing.
set +f
}” dir=”auto”>

# 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 '%sn' "$*"

    # Re-enable globbing.
    set +f
}

$ trim_all "    Hello,    World    "
Hello, World

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

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

    *sub_string2*)
        # Do other stuff
    ;;

    *)
        # Else
    ;;
esac

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

    sub_string2*)
        # Do other stuff
    ;;

    *)
        # Else
    ;;
esac

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

    *sub_string2)
        # Do other stuff
    ;;

    *)
        # Else
    ;;
esac

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 '%sn' "$@"

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

    # Re-enable globbing.
    set +f
}

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

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

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 '%sn' "$*"

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

    # Re-enable globbing.
    set +f
}

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

# Setting 'IFS' tells 'read' where to split the string.
while IFS='=' read -r key val; do
    # Skip over lines containing comments.
    # (Lines starting with '#').
    [ "${key###*}" ] || continue

    # '$key' stores the key.
    # '$val' stores the value.
    printf '%s: %sn' "$key" "$val"

    # Alternatively replacing 'printf' with the following
    # populates variables called '$key' with the value of '$val'.
    #
    # NOTE: I would extend this with a check to ensure 'key' is
    #       a valid variable name.
    # export "$key=$val"
    #
    # Example with error handling:
    # export "$key=$val" 2>/dev/null ||
    #     printf 'warning %s is not a valid variable namen' "$key"
done < "file"

head() {
    # Usage: head "n" "file"
    while IFS= read -r line; do
        printf '%sn' "$line"
        i=$((i+1))
        [ "$i" = "$1" ] && return
    done < "$2"

    # 'read' used in a loop will skip over
    # the last line of a file if it does not contain
    # a newline and instead contains EOF.
    #
    # The final line iteration is skipped as 'read'
    # exits with '1' when it hits EOF. 'read' however,
    # still populates the variable.
    #
    # This ensures that the final line is always printed
    # if applicable.
    [ -n "$line" ] && printf %s "$line"
}

$ head 2 ~/.bashrc
# Prompt
PS1='➜ '

$ head 1 ~/.bashrc
# Prompt

lines() {
    # Usage: lines "file"

    # '|| [ -n "$line" ]': This ensures that lines
    # ending with EOL instead of a newline are still
    # operated on in the loop.
    #
    # 'read' exits with '1' when it sees EOL and
    # without the added test, the line isn't sent
    # to the loop.
    while IFS= read -r line || [ -n "$line" ]; do
        lines=$((lines+1))
    done < "$1"

    printf '%sn' "$lines"
}

count() {
    # Usage: count /path/to/dir/*
    #        count /path/to/dir/*/
    [ -e "$1" ] 
        && printf '%sn' "$#" 
        || printf '%sn' 0
}

# Count all files in dir.
$ count ~/Downloads/*
232

# Count all dirs in dir.
$ count ~/Downloads/*/
45

# Count all jpg files in dir.
$ count ~/Pictures/*.jpg
64

Alternative to the dirname command.

Example Function:

dirname() {
    # Usage: dirname "path"

    # If '$1' is empty set 'dir' to '.', else '$1'.
    dir=${1:-.}

    # Strip all trailing forward-slashes '/' from
    # the end of the string.
    #
    # "${dir##*[!/]}": Remove all non-forward-slashes
    # from the start of the string, leaving us with only
    # the trailing slashes.
    # "${dir%%"${}"}": Remove the result of the above
    # substitution (a string of forward slashes) from the
    # end of the original string.
    dir=${dir%%"${dir##*[!/]}"}

    # If the variable *does not* contain any forward slashes
    # set its value to '.'.
    [ "${dir##*/*}" ] && dir=.

    # Remove everything *after* the last forward-slash '/'.
    dir=${dir%/*}

    # Again, strip all trailing forward-slashes '/' from
    # the end of the string (see above).
    dir=${dir%%"${dir##*[!/]}"}

    # Print the resulting string and if it is empty,
    # print '/'.
    printf '%sn' "${dir:-/}"
}

Example Usage:

$ dirname ~/Pictures/Wallpapers/1.jpg
/home/black/Pictures/Wallpapers/

$ dirname ~/Pictures/Downloads/
/home/black/Pictures/

Get the base-name of a file path

Alternative to the basename command.

Example Function:

basename() {
    # Usage: basename "path" ["suffix"]

    # Strip all trailing forward-slashes '/' from
    # the end of the string.
    #
    # "${1##*[!/]}": Remove all non-forward-slashes
    # from the start of the string, leaving us with only
    # the trailing slashes.
    # "${1%%"${}"}:  Remove the result of the above
    # substitution (a string of forward slashes) from the
    # end of the original string.
    dir=${1%${1##*[!/]}}

    # Remove everything before the final forward-slash '/'.
    dir=${dir##*/}

    # If a suffix was passed to the function, remove it from
    # the end of the resulting string.
    dir=${dir%"$2"}

    # Print the resulting string and if it is empty,
    # print '/'.
    printf '%sn' "${dir:-/}"
}

Example Usage:

$ basename ~/Pictures/Wallpapers/1.jpg
1.jpg

$ basename ~/Pictures/Wallpapers/1.jpg .jpg
1

$ basename ~/Pictures/Downloads/
Downloads

Loop over a (small) range of numbers

Alternative to seq and only suitable for small and static number ranges. The number list can also be replaced with a list of words, variables etc.

# Loop from 0-10.
for i in 0 1 2 3 4 5 6 7 8 9 10; do
    printf '%sn' "$i"
done

Loop over a variable range of numbers

Alternative to seq.

# Loop from var-var.
start=0
end=50

while [ "$start" -le "$end" ]; do
    printf '%sn' "$start"
    start=$((start+1))
done

Loop over the contents of a file

while IFS= read -r line || [ -n "$line" ]; do
    printf '%sn' "$line"
done < "file"

Loop over files and directories

Don’t use ls.

CAVEAT: When the glob does not match anything (empty directory or no matching files) the variable will contain the unexpanded glob. To avoid working on unexpanded globs check the existence of the file contained in the variable using the appropriate file conditional. Be aware that symbolic links are resolved.

# Greedy example.
for file in *; do
    [ -e "$file" ] || [ -L "$file" ] || continue
    printf '%sn' "$file"
done

# PNG files in dir.
for file in ~/Pictures/*.png; do
    [ -f "$file" ] || continue
    printf '%sn' "$file"
done

# Iterate over directories.
for dir in ~/Downloads/*/; do
    [ -d "$dir" ] || continue
    printf '%sn' "$dir"
done

Name and access a variable based on another variable

$ var="world"
$ eval "hello_$var=value"
$ eval printf '%sn' "$hello_$var"
value

Contrary to popular belief, there is no issue in utilizing raw escape sequences. Using tput abstracts the same ANSI sequences as if printed manually. Worse still, tput is not actually portable. There are a number of tput variants each with different commands and syntaxes (try tput setaf 3 on a FreeBSD system). Raw sequences are fine.

Text Colors

NOTE: Sequences requiring RGB values only work in True-Color Terminal Emulators.

Text Attributes

Cursor Movement

Erasing Text

Prefix and Suffix Deletion

Length

Default Value

For use in [ ] if [ ]; then and test.

File Conditionals

Variable Conditionals

Variable Comparisons

Assignment

Arithmetic

Bitwise

Logical

Miscellaneous

Ternary Tests

# Set the value of var to var2 if var2 is greater than var.
# 'var2 > var': Condition to test.
# '? var2': If the test succeeds.
# ': var': If the test fails.
var=$((var2 > var ? var2 : var))

Check if a number is a float

Example Function:

is_float() {
    # Usage: is_float "number"

    # The test checks to see that the input contains
    # a '.'. This filters out whole numbers.
    [ -z "${1##*.*}" ] &&
        printf %f "$1" >/dev/null 2>&1
}

Example Usage:

$ is_float 1 && echo true
$

$ is_float 1.1 && echo true
$ true

Check if a number is an integer

Example Function:

is_int() {
    # usage: is_int "number"
    printf %d "$1" >/dev/null 2>&1
}

Example Usage:

$ is_int 1 && echo true
$ true

$ is_int 1.1 && echo true
$

Traps allow a script to execute code on various signals. In pxltrm (a pixel art editor written in bash) traps are used to redraw the user interface on window resize. Another use case is cleaning up temporary files on script exit.

Traps should be added near the start of scripts so any early errors are also caught.

Do something on script exit

# Clear screen on script exit.
trap 'printf \033[2J\033[H\033[m' EXIT

# Run a function on script exit.
# 'clean_up' is the name of a function.
trap clean_up EXIT

Ignore terminal interrupt (CTRL+C, SIGINT)

Command Substitution

Use $() instead of ` `.

# Right.
var="$(command)"

# Wrong.
var=`command`

# $() can easily be nested whereas `` cannot.
var="$(command "$(command)")"

Open the user's preferred text editor

"$EDITOR" "$file"

# NOTE: This variable may be empty, set a fallback value.
"${EDITOR:-vi}" "$file"

Get the current working directory

This is an alternative to the pwd built-in.

Get the PID of the current shell

Get the current shell options

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