Rerunning commands

History

Lists all commands previously run in the shell:

  • HISTSIZE env var determines how many commands are saved, 500 by default.
  • Set custom HISTSIZE in .bashrc. -1 is unlimited.
  • Commands are saved unevaluted. For example, echo $HOME
  • HISTCONTROL lets you manage which commands are saved
  • HISTCONTROL=ignoredups does not save identical, consecutive commands.
  • Each shell has its own, separate history
  • HISTFILE is where the shell writes history, usually $HOME/.bash_history
    • When a shell exits, it writes history to HISTFILE
    • When a new shell starts, it loads HISTFILE as its history
history                         # print all shell history
history 5                       # print last 5 commands
history | less                  # pipe to less
history | sort -nr | less       # earliest to latest
history | grep -w cd            # print commands with 'cd'
history -c                      # clear history for current shell

History expansion

Lets you access shell history with special expressions:

!!                      # most recent command
!grep                   # most recent command that began with grep
!?grep?                 # most recent command that contained grep
!8                      # run 8th command in history
!-2                     # run command executed 2 commands ago
!-2:p                   # print but do not run command executed 2 commands ago
!$                      # final arg in previous command
!*                      # all args in previous command

# alternative to alias="rm -i"
ls <file-pattern>       # confirm returns files to delete
rm !$                   # delete files with final arg in previous command

Lets you type a few characters of a command and the rest appears instantly, like autocomplete:

  • CTRL + R starts the interactive prompt, and it cycles through all matching options
  • CTRL + G or CTRL + C exits the interactive prompt
  • Enter executes the command

Fixing mistakes

^wrong^right            # correct error in previous command (caret syntax)
!!:s/wrong/right/       # substitution with history expansion

vim- or emacs-style editing

A powerful way to edit a command line is with vim or emacs commands. By default, the shell uses emacs:

  • press Esc to enter editor-style mode
  • change style with set -o <editor>. Add to .bashrc to make it permanent
set -o vi               # use vi style
set -o emacs            # use emacs style