SamatsWiki

• Diff for "Bash"

Interesting bash aliases and functions:

• Cdots

• SSH to CWD on a remote server

• cd to project directory

• https://github.com/Bash-it/bash-it: Community bash "framework"

• Google's shell script style guide. Also good is Bash 3 Boilerplate

Neat features

Edit a command in $EDITOR

Ctrl-x Ctrl-e will edit a command in $EDITOR before execution.

With set -o vi in bash/readline, v in command mode will do the same.

-v for testing set variables, while handling undefined ones

-v: True if the shell variable varname is set (has been assigned a value).

bash >=4.2 supports -v for testing for *set* variables while handling empty ones, also no specials needs when running under 'set -u':

   1 % cat foo
   2 FOO=''
   3 [ -z "${FOO:-}" ] && echo 1
   4 [ -z "${BAR:-}" ] && echo 2
   5 [ -v FOO ] && echo 3
   6 [ -v BAR ] && echo 4
   7 % bash -u ./foo
   8 1
   9 2
  10 3

source

also:

If you use bash, you should really use ]] instead of [ ]. It can do everything [ can (and then some, like ERE and glob matches), but is a shell keyword, which improves ergonomics quite a bit. See [ $x = 0 ] vs. [[ $x = 0 after unset x, for example.

Special Variables

• $0 - The filename of the current script. Do not use!

• $n - The Nth argument passed to script was invoked or function was called. E.g. $1, etc.

• $# - The number of argument passed to script or function.

• $@ - All arguments passed to script or function.
• $* - All arguments passed to script or function.
• $? - The exit status of the last command executed.
• $$ - The process ID of the current shell. For shell scripts, this is the process ID under which they are executing.

• $! - The process number of the last background command.

• $- - current options set for the shell

• $_ - most recent parameter, or the absolute path of the command used to start the current shell

See Special Parameters from the Bash Reference Manual.

"Strict Mode"

• Unofficial Bash Strict Mode

Tools

Use shellcheck with timonwong.shellcheck plugin.

Use bash-language-server.

Gotchas

• Take care editing bash scripts: Bash processes scripts as they execute, so saving over a script that is running can have side effects.

Never Remember

Process Substition is the name for <(command) syntax.

Redirect stderr to stdout with 2>&1, e.g.:

Some-Command 2>&1 > log.txt