telegram-bot-bash/doc/5_practice.md
2020-10-16 10:53:08 +02:00

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Best Practices

New to bot development?

If you are new to Bot development read Bots: An introduction for developers and consult Telegram Bot API Documentation.

In addition you should know about BotFather, the one bot to rule them all. It will help you create new bots and change settings for existing ones. Commands known by Botfather

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Add commands to mycommands.sh only

Do not change bashbot.sh and commands.sh, instead place your commands in to mycommands.sh. To start with a clean/minimal bot copy mycommands.sh.clean to mycommands.sh and start editing the message strings and place commands in thecase ... esac block of the function mycommands():

# file: mycommands.sh
# your additional bashbot commands

# uncomment the following lines to overwrite info and help messages
 bashbot_info='This is *MY* variant of _bashbot_, the Telegram bot written entirely in bash.
'

 bashbot_help='*Available commands*:
/echo message - _echo the given messsage_
'

# NOTE: command can have @botname attached, you must add * in case tests... 
mycommands() {

	case "$MESSAGE" in
		'/echo'*) # example echo command
			send_normal_message "${CHAT[ID]}" "$MESSAGE"
			;;
		# .....
	esac
}

DIsable, replace and extend global commands

Global bashbot command processing, e.g. /start, /info etc. is disabled if you return a non zero value from mycommands.sh, see /start example below.

To replace a global bashbot command add the same command to mycommands.sh and place return 1 at the end of the case block, see /kickme example below.

If a command is available as a global command and in mycommands.sh, plus you return a zero value (nothing or 0) both command sections are processed. Thus you can extend global commands with additional actions, see /info example below

Learn more about Bot commands.

# file: mycommands.sh

	case "$MESSAGE" in
		##########
		# disable start command
		'/start'*) # disable all commands starting with leave
			return 1
			;;
		# replace command with your own actions
		'/kickme'*) # this will replace the /kickme command
			send_markdown_mesage "${CHAT[ID]}" "*This bot will not kick you!*"
			return 1
			;;
		# extend global command
		'/info'*) # output date in front of regular info
			send_normal_message "${CHAT[ID]}" "$(date)"
			return 0
			;;
	esac

Separate logic from commands

If a command need more than 2-3 lines of code, you should use a function to separate logic from command. Place your functions in mycommands.sh and call the from your command. Example:

# file: mycommands.sh
# your additional bashbot commands

mycommands() {

	case "$MESSAGE" in
		'/doit'*) # logic for /doit is done in process_message 
			result="$(process_message "$MESSAGE")"
			send_normal_message "${CHAT[ID]}" "$result" 
			;;
	esac

}

# place your functions here

process_message() {
   local ARGS="${1#/* }"	# remove command 
   local TEXT OUTPUT=""

   # process every word in MESSAGE, avoid globbing
   set -f
   for WORD in $ARGS
   do
	# process links 
	if [[ "$WORD" == "https://"* ]]; then
		REPORT="$(dosomething_with_link "$WORD")"
	# no link, add as text
	else
		TEXT="$(echo "${TEXT} $WORD")"
		continue
	fi
	# compose result
	OUTPUT="* ${REPORT} ${WORD} ${TEXT}"
	TEXT=""
   done

   # return result, reset globbing in case we had no ARGS
   echo "${OUTPUT}${TEXT}"
}

Test your Bot with shellcheck

Shellcheck is a static linter for shell scripts providing excellent tips and hints for shell coding pittfalls. You can use it online or install it on your system. All bashbot scripts are linted by shellcheck.

Shellcheck examples:

$ shellcheck -x mybotcommands.inc.sh
 
Line 17:
                TEXT="$(echo "${TEXT} $WORD")"
                      ^-- SC2116: Useless echo? Instead of 'cmd $(echo foo)', just use 'cmd foo'.
 

As you can see my mybotcommands.inc.sh contains an useless echo command in 'TEXT=' assignment and can be replaced by TEXT="${TEXT}${WORD}"

$ shellcheck -x examples/notify
OK
$ shellcheck -x examples/question
OK
$ shellcheck -x commands.sh
OK
$ shellcheck -x bashbot.sh

In bashbot.sh line 123:
                text="$(echo "$text" | sed 's/ mynewlinestartshere /\r\n/g')" # hack for linebreaks in startproc scripts
                        ^-- SC2001: See if you can use ${variable//search/replace} instead.


In bashbot.sh line 490:
        CONTACT[USER_ID]="$(sed -n -e '/\["result",'$PROCESS_NUMBER',"message","contact","user_id"\]/  s/.*\][ \t]"\(.*\)"$/\1/p' <"$TMP")"
        ^-- SC2034: CONTACT appears unused. Verify it or export it.

The example show two warnings in bashbots scripts. The first is a hint you may use shell substitutions instead of sed, this is fixed and much faster as the "echo | sed" solution. The second warning is about an unused variable, this is true because in our examples CONTACT is not used but assigned in case you want to use it :-)

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