# bash
`bash` (Bourne-Again) is a shell.


# Configuration files
* ``.bash_profile:`` read on login
	* or .profile, or .bash_login
* ``.bashrc:`` read on subshell start
* ``.bash_logout:`` read on login shell exit


# Functions
You can define functions in a bash script like so:
```sh
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:
```sh
#!/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. 


# Parameter expansion
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:
```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=$(( FileNumber + 1 ))                     #   10
NextNumberWithLeading0s=$(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
```
			
			

See also
--------
* [hypexr.org - Bash Help](https://www.hypexr.org/bash_tutorial.php) 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