bash (Bourne-Again) is a shell.

• .bash_profile: read on login
  • or .profile, or .bash_login
• .bashrc: read on subshell start
• .bash_logout: read on login shell exit

You can define functions in a bash script like so:

hello()
{
	echo 'Hello, world'
}

And call it with hello. Be careful that it doesn't conflict with another program! (prefix it with something, just in case)
You can pass arguments to a function just like a shell script with hello arg1 arg2. These are available as expected: $1 and $2 respectively.

In bash, functions can't have prototypes. So, for readability, you can structure your program like this:

#!/bin/bash
 
main() {
	hello
	goodbye
}
 
hello() {
}
 
goodbye() {
}
 
main "$@"

The last line actually begins execution of the script from the main function while passing it the script's arguments.

Taken from Wooledge bashFAQ:
parameter result

$file /usr/share/java-1.4.2-sun/demo/applets/Clock/Clock.class
${file#/} usr/share/java-1.4.2-sun/demo/applets/Clock/Clock.class
${file##/} Clock.class
${file///}\\ ${file%///} /usr/share/java-1.4.2-sun/demo/applets/Clock ${file%.mp3} filename without mp3 extension More examples: <code sh> FullPath=/path/to/name4afile-009.ext # result: # /path/to/name4afile-009.ext Filename=${FullPath##*/} # name4afile-009.ext PathPref=${FullPath%"$Filename"} # /path/to/ FileStub=${Filename%.*} # name4afile-009 FileExt=${Filename#"$FileStub"} # .ext FnumPossLeading0s=${FileStub##*[![:digit:]]} # 009 FnumOnlyLeading0s=${FnumPossLeading0s[!0]*} # 00 FileNumber=${FnumPossLeading0s#“$FnumOnlyLeading0s”} # 9 NextNumber=$¹⁾ # 10 NextNumberWithLeading0s=$(printf “%0${#FnumPossLeading0s}d” “$NextNumber”)

                                                   #   010

FileStubNoNum=${FileStub%“$FnumPossLeading0s”} # name4afile- NewFullPath=${PathPref}New_${FileStubNoNum}${NextNumberWithLeading0s}${FileExt} # Final result is: # /path/to/New_name4afile-010.ext </code>

• hypexr.org - Bash Help for a starter on bash usage.

Afterwards, you can delve into http://mywiki.wooledge.org/BashGuide for a more complete guide (also shell scripting). The http://mywiki.wooledge.org/BashFAQ and http://mywiki.wooledge.org/BashPitfalls are especially useful

https://guide.bash.academy/inception/ → WIP guide on bash and shell scripting