# shortcuts

    alt-backspace   # delete left word
    ctrl-t          # swap last two chars, readline emacs mode
    alt + .         # cylcle through last arguments


# special parameters

    $?    # last exit code
    $!    # pid of last background proc
    !!    # last/previous command
    !$    # first of last arguments
    !*    # all last arguments
    ~-    # previous directory


# history

    !!          # execute last command in history
    ^foo^bar    # execute last command after replacing foo w/ bar
    !abc        # execute last command in history beginning w/ 'abc'
    !abc:p      # print last command in history beginning w/ 'abc'
    ctrl-r      # search in history
    ctrl-g      # exit history search


# redirection

connect stdout or stdout and stderr of `command1` to stdin of `command2` with

    command1 | command2
    command1 |& command2    # shorthand for:
    command1 2>&1 | command2

predefined 0 `stdin`, 1 `stdout`, 2 `stderr`.

    command 2>/dev/null
    command 1>&2
    command >/dev/null 2>&1

`>` overwrites while `>>` appends to file.
*process substitution* puts output in named fifo which can be used like a file by other process:
`cat <( echo hello )`.
doesn't work w/ `source` before bash 3.2, workaround:
`. /dev/stdin <<<"$( echo 'PS1=yep' )"`.


# path expansion

additional to globbing there's extended globbing (`shopt extglob`).

    # match all files w/o `.` in their filenames
    ls +([^.])


# parameter expansion

## remove matching pre/suffix

    ${a#pattern}    # prefix
    ${a##pattern}   # greedy
    ${a%pattern}    # suffix

## case modification

    ${a,,pattern}   # lowercase all chars in `$a` that match pattern
    ${a,,}          # same as `${a,,?}`
    ${a,pattern}    # lowercase only first matching char
    ${a^pattern}    # uppercase


# variables

By convention, environment variables (`PAGER`, `EDITOR`, ...) and internal
shell variables (`SHELL`, `BASH_VERSION`, ...) are capitalized. All other
variable names should be lower case.
*If it's your variable, lowercase it. If you export it, uppercase it.*


# builtins

```sh
help [name]
command -v <name>   # like `which` w/o error message
type [name]         # display information about command type, includes function body
declare -F [name]   # display declared function names
declare -f [name]   # display declared function including body
read var            # read one line from stdin into `var`
typeset             # (deprecated?) synonym for `declare`
```


# includes

`.` is the Bourne and POSIX shell command while `source` is the C-Shell command.


# unsorted

dollar sign before string triggers special char evaluation, f.e.: `$'\n'`

create sequence w/ `{3..9}`

figure out running shell session:
```
[[ $- == *i* ]] && echo 'Interactive' || echo 'Not interactive'
[[ -o login ]] && echo 'Login shell' || echo 'Not login shell'
```


## function return value w/ `declare`

    [0] $ function marius () { declare -n var=$1; var='xxx'; }
    16:05:07 heiko@bonn:~
    [0] $ msg=
    16:05:19 heiko@bonn:~
    [0] $ marius msg
    16:05:28 heiko@bonn:~
    [0] $ echo $msg
    xxx