lightshot-print-screen

#!/bin/sh

################################################################################
#                                                                              #
#                Project: Lightshot print screen Linux handler                 #
#                ---------------------------------------------                 #
#                    GitHub: https://burian.work/lightshot                     #
#                           Code: POSIX shell script                           #
#                                 License: MIT                                 #
#                            Released: 2026-May-21                             #
#                      Version: 10.2 (2nd final for X11)                       #
#                       E-mail: info@vlastimilburian.cz                        #
#                  Copyright: (c) 2018-2026 Vlastimil Burian                   #
#                                                                              #
################################################################################

# The hotkey variable is on top for easy set-up; overridable with -k switch, see a short example with -h.
# Run this script first on terminal to test it out, it will print out if Lightshot was (not) found running.
# Set it to the same hotkey which you have set up in your Lightshot options, by default there is Print.
# Example: for the left control key and the print screen key put Control_L+Print in the hotkey variable.
hotkey='Print'

# Treat unset variables as errors when substituting.
# Clarification: this means that accessing any unassigned variable
# produces immediate termination of the script with an error printed.
set -o nounset

# (bool) Function to test one argument for an integer.
is_int()
{
    case "${1#[+-]}" in
        (*[!0123456789]*) return 1 ;;
        ('')              return 1 ;;
        (*)               return 0 ;;
    esac
}

# (bool) Function to test one argument for an unsigned integer.
is_uint()
{
    case "$1" in
        ([+-]*) return 1 ;;
    esac

    is_int "$1"
}

# (bool) Function to test one argument for a _safe_ exit code:
# _Safe_ exit code must be an unsigned integer from the range of <0;125> which is considered
# the safe range, the remaining range of <126;255> is reserved or otherwise not recommended.
is_safe_exit()
{
    is_uint "$1" && [ "$1" -le 125 ]
}

# (string) Function to detect basic argument types passed to my functions:
# empty, integer, file (with specific info), the rest is considered string.
dump_args()
{
    # we do not write anything for 0 arguments
    [ "$#" -eq 0 ] && return 1
    i=1
    printf '%s\n' \
        "dump_args()" \
        "$# arguments inspected:"
    while [ "$#" -gt 0 ]; do
        printf "[%d]: '%s' " "$i" "$1"
        if [ -z "$1" ]; then
            printf '%s' "(empty)"
        elif is_int "$1"; then
            printf '%s' "(integer)"
        elif [ -e "$1" ]; then
            printf '%s' "(file: $( file -b "$1" ))"
        else
            printf '%s' "(string)"
        fi
        printf '\n'
        shift
        i=$(( i + 1 ))
    done
} >&2

# (string) Function to print an error message.
error_print()
{
    printf '%s\n' \
        "Error heading: $1" \
        "Error message: $2"
} >&2

# (string) Function to print an error message and exit right away.
error()
{
    # Original logic waiting to be translated to the "opposite" logic:
    if ! { [ "$#" -eq 2 ] && [ -n "$1" ] && [ -n "$2" ]; } &&
       ! { [ "$#" -eq 3 ] && [ -n "$1" ] && [ -n "$2" ] && [ "$3" -ge 1 ] && is_safe_exit "$3"; }; then
        dump_args "$@"
        # shellcheck disable=SC2016
        printf '%s\n' \
            'error() input check' \
            'Wrong number, type or empty arguments have been passed to the function.' \
            'Expected the following strings: $1 = error heading, $2 = error message.' \
            'Optionally, accepting a number: $3 = exit code; if not given 1 is used.' \
            'Acceptable exit code range: anywhere between <1;125>; 1 is the default.'
        exit 1
    fi
    error_print "$1" "$2"
    exit "${3:-1}"
} >&2

user_id()
{
    id -u
}

if [ "$( user_id )" -eq 0 ]; then
    error 'user_id()' 'Running this script with root privileges is not recommended! Expected an ordinary user.'
fi

dependencies()
{
    if [ "$#" -eq 0 ]; then
        error 'dependencies() input check' 'No arguments passed to the function! At least one program/package name pair expected.'
    fi
    if [ "$(( $# % 2 ))" -ne 0 ]; then
        dump_args "$@"
        error 'dependencies() input check' 'Odd number of arguments has been passed to the function. Program and package names in pairs expected.'
    fi

    dependency_missing=false

    while [ "$#" -gt 0 ]; do
        if ! command -v "$1" >/dev/null 2>&1; then
            dependency_missing=true
            error_print 'dependencies(): unmet required dependency' "This script requires '$1' program but it is not available on this system! On Ubuntu/Debian OS, just install the '$2' package; other systems may differ."
        fi
        shift 2
    done

    if "$dependency_missing"; then
        exit 1
    fi
}

dependencies \
    pgrep      procps \
    xdotool    xdotool

usage()
{
    if [ "$#" -ne 1 ] || ! is_safe_exit "$1"; then
        dump_args "$@"
        # shellcheck disable=SC2016
        error 'usage() input check' 'One number required: $1 = exit code from the script.'
    fi

    # conditional redirect to stderr, depending on zero (stdout) / stderr (non-zero) exit code
    [ "$1" -ne 0 ] && exec >&2

    cat <<EOF
Project: Lightshot print screen Linux handler
Version: 10.2 (2nd final for X11) released 2026-May-21
GitHub : https://burian.work/lightshot
--------------------------------------------------------------------
Description: This script works with XDOTOOL to trigger Print Screen
key combination in Lightshot application installed on Linux in Wine.
The script however will not launch Lightshot for you due to variable
installation locations which make it impossible. You need to run it!
License is MIT. The code can be further enhanced by others provided
that any new copies have my copyright notice included in every case.
--------------------------------------------------------------------
Usage in terminal: ./$( basename "$0" ) [-k HotKey]

    -k HotKey: Optional switch requiring one argument,
        which is the print screen hotkey combination.
        For the left Control key and the Print Screen key
        that would be -k Control_L+Print (as an example).

    -h: Show this help.

Usage in desktop environment:

    You need to find Keyboard shortcuts, and re-map Print to run
    this script, an example from Linux Mint is placed on GitHub.

Author:
    Copyright 2018-2026
    Vlastimil Burian
    info@vlastimilburian.cz
EOF

    exit "$1"
}

while getopts ':hk:' option; do

    case "$option" in

        (k)
            hotkey=$OPTARG
        ;;

        (h)
            usage 0
        ;;

        (*)
            dump_args "$@"
            usage 1
        ;;

    esac

done
shift $(( OPTIND - 1 ))

if [ "$#" -ne 0 ]; then
    dump_args "$@"
    usage 1
fi

get_process_id()
{
    if [ "$#" -ne 1 ] || [ -z "$1" ]; then
        dump_args "$@"
        # shellcheck disable=SC2016
        error 'get_process_id() input check' 'String required: $1 = a process name to find id to.'
    fi
    #-o, --oldest: least recently started
    #-u, --euid  : match by effective UID
    pgrep "$1" -o -u "$( user_id )"
}

get_window_id()
{
    if [ "$#" -ne 2 ] || ! is_uint "$1" || [ -z "$2" ]; then
        dump_args "$@"
        error 'get_window_id() input check' 'Two valid arguments were not passed to the function! Expected a process id (unsigned integer) and a window name (string).'
    fi
    #--all  : Require all conditions to be met.
    #--sync : Wait until a search result is found.
    #--limit: Stop searching after finding N matching windows.
    #--pid  : Match windows that belong to a specific process id.
    #--name : Match against the window name. This is the same string that is displayed in the window titlebar.
    if ! xdotool search --all --sync --limit 1 --pid "$1" --name "$2"; then
        error 'get_window_id()' "No window matching process id '$1' and window name '$2' has been found."
    fi
}

# The Lightshot file name is case-sensitive.
lightshot_process_id=$( get_process_id Lightshot.exe )

if ! is_uint "$lightshot_process_id"; then
    # shellcheck disable=SC2016
    error 'is_uint $lightshot_process_id' 'Lightshot process is not running. Launch Lightshot app first, please.'
fi

# The Lightshot window name is case-insensitive.
lightshot_window_id=$( get_window_id "$lightshot_process_id" Lightshot )

if ! is_uint "$lightshot_window_id"; then
    # shellcheck disable=SC2016
    error 'is_uint $lightshot_window_id' 'Lightshot process was found (is running) but its window was not found for some reason / get_window_id() returned an empty value.'
fi

if xdotool key --window "$lightshot_window_id" "$hotkey"; then
    printf '%s\n' \
        "Success, the hotkey = $hotkey was successfully sent to Lightshot window!" \
        'If the Lightshot overlay did not appear, you likely sent a wrong hotkey.' \
        'In such a case, please adjust the hotkey in Lightshot tray options menu.'
else
    error "xdotool key --window $lightshot_window_id $hotkey" 'The above send-hotkey command encountered an unknown error.'
fi