# `bash` tips/tricks/HOWTOs

## HOWTO: Read exit status

You can just do things like:

	 if cp $1 $2 ; then
	   echo succeeded
	 else
	   echo failed
	 fi
  
Alternatively, <tt>$?</tt> holds the exit status of the most recently executed
command.

## TIP: Command substitution

	`command`
  
or

	$(command)

## TIP: Redirection

To redirect stdout to <tt>/dev/null</tt>, and stderr to the tty:

	$ tidy index.html 2>/dev/stdout 1>/dev/null

## TIP: Parameter expansion

    ${foo}
    
or

    $foo
    
## TIP: `$FUNCNAME` contains the current function name

The `$FUNCNAME` variable is set to the name of the function while the
function is executing.  (i.e. like `$0`, except the name of the
function, rather than the name of the script.)

## TIP: `$BASH_SOURCE` contains the current filename

If you want to discover the real path of the current filename (i.e.
after resolving symbolic links), use `readlink`:

    echo $(readlink $BASH_SOURCE)

Note that `$BASH_SOURCE` is actually an array, but when treated as a
scalar, it returns the first element of the array.

## HOWTO: Perform conditional variable assignment

If `$1` exists, assign `$CONFIGROOT` its value, otherwise set
`$CONFIGROOT` to `$HOME/.config`:

    CONFIGROOT=${1:-$HOME/.config}

## TIP: `sudo !!`

Repeats the last command under `sudo`.

## HOWTO: In a shell script, ensure a temporary file is deleted

    TEMPFILE=$(mktemp)
    trap "rm -rf $TEMPFILE" EXIT

`$TEMPFILE` will be removed in almost all circumstances when the shell
exits, including Ctrl-C.

## HOWTO: Display current/existing keybindings

    bind -P

The escape sequences are defined as follows:

    \C-    control prefix
    \M-    meta prefix
    \e     an escape character
    \\     backslash
    \"     literal "
    \'     literal '

You can also use `TAB` for the tab character.  (May or may not be the
same as `\t`, below.

In  addition  to  the  GNU  Emacs style escape sequences, a second set of 
backslash escapes is available:

    \a     alert (bell)
    \b     backspace
    \d     delete
    \f     form feed
    \n     newline
    \r     carriage return
    \t     horizontal tab
    \v     vertical tab
    \nnn   the eight-bit character whose value is the octal value  nnn  (one  to
           three digits)
    \xHH   the  eight-bit character whose value is the hexadecimal value HH (one
           or two hex digits)