Bash

• It is a literal string. No need to escape. No substitutionse letter is in the bracket.

  • a-z A-Z 0-9 range
  • :alnum: :alpha: :ascii: :digit: :space: :lower: :upper: …
  • =c= match the equivalence class with the collation weight. .symbol. match collating symbol.
  • ?(PATTERNS) match once, *(PATTERNS) match zero or more times, +(PATTERNS) match one or more times, @(PATTERNS) match one of the patterns, !(PATTERNS) does not match any pattern.

• {,STRING1,STRING2,...}
  • Expand into words containing each STRING
• {START..END[..STEP]} for sequences.

• ~ home directory of the current user
• ~user home directory of the user
• ~+ $PWD, ~- $OLDPWD
• ~N ~+N N=th previous directory in the directory stack, =~-N =N=th oldest directory in the directory stack
  • The directory stack is created with pushd and popd
• type
• Shell builtin that returns the type of the commands.
• shell keyword shell builtin

• * and @ expands differently, on double-quoted expansion. They would expand into multiple strings regardless without double-quotes.

  • @: the elements expand into multiple strings, with the first

  argument and last argument joined with the surrounding strings.

  • *: the elements expand into single string joined by

  ${IFS:0:1}.

• ((STATEMENT))
• $((EXPRESSION))
• expr
• let evaluate arithmetic statements

case STRING in
    PATTERN)
      COMMANDS
    PATTERN)
        COMMANDS
    *)
      COMMANDS
esac

$RANDOM generate a pseudorandom number.

• ( COMMANDS ) the commands are run in a subshell, and the output is returned in one string.
  • ( is an operator. whitespace is not necessary.
• { COMMANDS } the commands are run in the current context.
  • { is a shell keyword. Must be separated by whitespace.

• Plain inline
• It leaves the output of commands with multiple outputs as is.

• echo printf
• read VARIABLE read the user input into the VARIABLE

• export

  • shell builtin (internal)
  • export(1P) help export
  • set export attribute of a shell variables.
  • The exported variables are then set as the environment variables

  of the child processes.

• It applies to the commands that is being run. Not the shell itself.

• [n-1]>[|]FILENAME

  • File Descriptor <-> File
  • Write the stdout(1) of previous command to a file.
  • If noclobber shopt is set, it does not write to a existing

  file, >| force the write.

• [n-0]<FILENAME
  • Open it as fd/n
• [n-1]>>FILENAME
  • Append the stdout(1) of previous command to a file.
• &>FILENAME
  • Redirect both the stdout(1) and stderr(2) to the file.
• &>>FILENAME
  • Append
• [n-0]<>FILENAME
  • file is opened as file descriptor n for both read and write.
• [n-0]<<[-]DELIMITER
  • Here Documents
  • Write the content directly into the command line until specified DELIMITER appears.
  • If the delimiter is quoted ("<DELIMITER>"), text is used verbatim
  • <<- makes it indent aware, and remove it.
• [n-0]<<<WORD
  • WORD gets expanded and supplied directly.
• [n-0]<&{m|-}
  • File descriptor <-> File Descriptor
  • n becomes the copy of the file descriptor m. n is closed if -.
  • [n-1]>&{m|-} n becomes the copy of the m
  • [n-0]<&m- The file descriptor m is moved to n, and m is removed.
  • [n-1]>&m- m is moved to n
• |
  • Take the stdout(1) of previous command and feed it to the stdin(0) of the next command.

• cd
• pushd popd
  • cd -N to pop to Nth directory in stack. <tab> to see the candidates.
• pwd print current working directory

• fc edit and execute history entries (POSIX)
  • -e set editor
  • -l list history
  • -s execute last match
• history
  • Manage history entries

They have the form EVENT[WORD|MODIFIER]

• Event Designator
  • !!
    • It refers to the previous command.
  • !#
    • Every commands before this token, on the same line.
  • !N
    • positive number n refers to the n th command from the initialization.
    • negative number -n refers to the n th command previous to current line.
  • !PREFIX match last command with PREFIX

• : Word Designator
  • N n th word
  • ^, $ first or last argument

• : modifiers
  • s/.../.../ replace

• History Interaction (Bash Reference Manual)

• ^OLD^NEW[^|\n]
  • Substitute on the previous command

• /etc/bash.bashrc
• ~/.bashrc
  • Only loaded when the shell is interactive ($- != *i*)

• complete shell builtin (Bash only)

  • -p NAME the completion specification for NAME
  • search compspec for the full pathname, search compspec for the

  portion after final slash, then compspec defined as the default with -D is used.

  • -G GLOBPATTERN
  • -W WORDLIST NAME
  • -F FUNCTION NAME the completions are returned in COMPREPLY

  array variable.

  • -C COMMAND
  • -P PREFIX
  • -S SUFFIX

• bash-completion

  • This package uses complete to make additional autocompletion.
  • It is bunch of shell scripts, that needs to be sourced on

  startup. The entry point is /usr/share/bash-completion/bash_completion.

  • _comp_complete_load loads the additional compspec from CMD

  or CMD.bash, that is not set by default, defined in

  • ~/.local/share/bash-completion/completions/
  • /usr/share/bash-completion/completions/

• bind (Bash only)
  • Configure the Readline settings
  • -m {emacs|vi|...} set the keybindings
  • -v -V, (human readable) list Readline variables.
• Bash uses Readline library for its input. It allows the user to modify the commands in place.
• The configuration file is /etc/inputrc and ~/.inputrc
  • The configuration is in the form set VAR VAL

• Emacs and Vim insert mode bindings
  • <C-r> <C-s> search
  • <C-w> delete back a word

• PS1 is the prompt format.
• PS2 is the continuation prompt format.

• It sets the prompt based on the context, using the starship binary to generate various shell scripts and prompt formats.
• It uses ((669c3baf-f6d5-4176-86b3-139a00084b7f)).
• Starship is compatible with many other shells, including , , Powershell, etc.