Aliases vs Functions

Two ways to make a shortcut

An alias is a string substitution. alias ll='ls -lah' means "when I type ll, run ls -lah." A function is a small program. It takes arguments, has its own logic, can call other commands.

Alias rules

• alias name='command' — definition.
• No spaces around =.
• Quote the value (single quotes preferred).
• Aliases can't take arguments naturally — they're plain text replacement.
• unalias name — remove.
• alias with no args — list every alias.

Function rules

• name() { commands; } — POSIX form.
• function name { commands; } — bash/zsh.
• $1, $2, ... are arguments. $@ all of them.
• local var=value keeps a variable inside the function.
• unset -f name — remove.

When to use which

• Need to add a flag to a command? → alias.
• Need to manipulate arguments? → function.
• More than one line? → function.
• Quick one-letter shortcut for a long command? → alias.

Common patterns

alias ll='ls -lah'
alias gst='git status'
alias gco='git checkout'
alias ports='lsof -iTCP -sTCP:LISTEN -P -n'

mkcd() { mkdir -p "$1" && cd "$1"; }
extract() {
  case "$1" in
    *.tar.gz|*.tgz) tar xzf "$1" ;;
    *.zip)          unzip "$1" ;;
    *.tar.bz2)      tar xjf "$1" ;;
    *) echo 'unknown archive' ;;
  esac
}