Shell history, aliases, and functions

Small shell-quality investments — better history, well-chosen aliases, named functions — repay themselves every day.

Shell history

Bash records every interactive command in memory and writes the session to ~/.bash_history (or wherever HISTFILE points) when the shell exits.

$ history 5

   42  uname -r
43  systemctl status ssh
44  journalctl -u ssh --since '1 hour ago'
45  ls -la /etc/ssh
46  history 5

Useful keybindings (Emacs-style by default; switch to vi with set -o vi):

Aliases

An alias is a name that expands to a command when typed:

$ alias ll=ls-lh; alias grep=grep-color-auto; alias rm=rm-i; alias

alias ll=ls-lh
alias grep=grep-color-auto
alias rm=rm-i
alias

Shell functions

A shell function is a named block of shell code that you can call later. Functions are available in scripts (unlike aliases) and can take arguments:

$ lso() { ls -lh "$@" | less -F; }; type lso

lso is a function
lso ()
{
ls -lh "$@" | less -F
}

A practical pattern for sysadmins — a function that wraps a complex diagnostic:

sysd-journal() {
    journalctl -u "$1" --since "${2:-1 hour ago}" --no-pager
}

Then: sysd-journal ssh '1 hour ago' or just sysd-journal ssh.

Where to put each

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