Add help message

printscreen

@@ -1,8 +1,11 @@
 #!/bin/sh
 
 ## Try to use flameshot to get a screenshot
+### Select area work with both NORMAL and DELAYED_MODE.
 ### See https://github.com/flameshot-org/flameshot
 ## Or try to use scrot
+### Select area work only in normal mode.
+### In DELAYED_MODE, a capture of all screens is made.
 
 # Vars {{{
 readonly PROGNAME=$(basename "${0}")
@@ -15,6 +18,34 @@ readonly RED='\033[0;31m'
 readonly RESET='\033[0m'
 readonly COLOR_DEBUG="${PURPLE}"
 # }}}
+usage() {                                                       # {{{
+
+	cat <<- EOF
+usage: $PROGNAME [--help] [--delay INT_DELAY_SECONDS] [INT_DELAY_SECONDS]
+
+Try to get a screen capture with available tool :
+  1. Flameshot (see : https://github.com/flameshot-org/flameshot)
+  2. Scrot
+
+EXAMPLES :
+    - Select the area, on the screen, to capture
+        ${PROGNAME}
+
+    - Wait 5 seconds before launching the capture tool
+        ${PROGNAME} 5
+        ${PROGNAME} --delay 5
+
+OPTIONS :
+    -d,--delay INT_DELAY_SECONDS
+        Wait INT_DELAY_SECONDS before launching capture tool
+
+    --help
+        Print this help message.
+
+EOF
+
+}
+# }}}
 debug_message() {                                               # {{{
 
 	local_debug_message="${1}"
@@ -59,9 +90,15 @@ if [ ! "${NBARGS}" -eq "0" ]; then
 			## Define the delay with this argument (in seconds)
 			delay_screenshot="${1}"
 			;;
+		-h|--help )            ## help
+			usage
+			## Exit after help informations
+			exit 0
+			;;
 		* )                    ## unknow option
 			printf '%b\n' "${RED}Invalid option: ${1}${RESET}"
 			printf '%b\n' "---"
+			usage
 			exit 1
 			;;
 	esac