alias / unalias

Defines an alias. There must be no spaces around the =.

alias name='command'

Lists all currently defined aliases.

alias

Shows the definition of a specific alias.

alias name

Removes an alias.

unalias name

Removes all aliases at once.

unalias -a

A basic example of defining and using an alias. The long command ls -la is given the shorter name ll.

alias ll='ls -la'
ll nerv_report.txt
-rw-r--r--  1 rei  nerv  1024 Apr  9 21:00 nerv_report.txt

Running alias with no arguments lists all currently defined aliases.

alias
alias ll='ls -la'
alias grep='grep --color=auto'
alias rm='rm -i'

Passing a specific alias name shows only that alias's definition.

alias ll
alias ll='ls -la'

Use unalias to remove an alias. After removal, the name is no longer recognized.

unalias ll
ll nerv_report.txt
-bash: ll: command not found

Defining several aliases at once. The following sets up useful aliases for NERV operations.

alias report='cat /var/log/nerv/angel_detection.log'
alias backup='cp eva_unit01.log eva_unit01.log.bak'
alias status='ps aux | grep eva'
alias nerv_home='cd /home/rei/nerv'
alias ll='ls -la --color=auto'

Persisting aliases in .bashrc

# Aliases to add to ~/.bashrc

# File navigation
alias ll='ls -la --color=auto'
alias la='ls -A'
alias ..='cd ..'
alias ...='cd ../..'

# Safety guards (prevent accidental overwrite/delete)
alias rm='rm -i'
alias cp='cp -i'
alias mv='mv -i'

# NERV operations
alias report='cat /var/log/nerv/angel_detection.log'
alias eva_log='tail -f /var/log/nerv/eva_unit01.log'
alias nerv_home='cd /home/rei/nerv'

After saving the file, reload it in the current session with source.

source ~/.bashrc

Aliases cannot take arguments. Use a function when you need argument handling.

NG: trying to pass an argument to an alias

# Alias cannot handle arguments
alias greet='echo "Hello, $1"'  # $1 is not expanded as an argument

$1 is expanded as a literal string when the alias is defined, so it cannot work as a runtime argument.

OK: nerv_report.sh (use a function when arguments are needed)

#!/bin/bash

nerv_report() {
    local target="$1"
    echo "=== NERV Report: $target ==="
    cat "/var/log/nerv/${target}.log"
}

nerv_report "angel_detection"
nerv_report "eva_unit01"

Aliases are only active in the current shell process. They are not inherited by subshells (such as inside scripts) by default. To use aliases inside a script, enable shopt -s expand_aliases (bash). That said, using aliases in scripts is uncommon — functions are generally preferred for their portability and readability.

You can shadow an existing command name (ls, grep, etc.) with an alias to automatically prepend options. To bypass the alias and call the original command, prefix the name with a backslash (\ls) or use command ls.

zsh supports alias -g (global aliases), which expand anywhere in a command line — not just at the beginning. For example, alias -g L='| less' lets you write cat file L. This feature is not available in bash.

Common Mistake 1: Spaces around the = sign

Adding spaces around = in an alias definition causes an error.

alias ll = 'ls -la'
alias ll='ls -la'
-bash: alias: ll: not found
-bash: alias: =: not found
-bash: alias: ls -la: not found

The shell treats ll, =, and 'ls -la' as separate arguments. Write the definition with no spaces around =.

alias ll='ls -la'

Common Mistake 2: Single quotes vs. double quotes change when variables are expanded

When you define an alias with single quotes, variable expansion happens when the alias is executed. With double quotes, expansion happens when the alias is defined.

export NERV_DIR="/home/rei/nerv"
alias go_nerv_single='cd $NERV_DIR'
alias go_nerv_double="cd $NERV_DIR"
export NERV_DIR="/home/shinji/nerv"
go_nerv_single
pwd
/home/shinji/nerv

With single quotes, $NERV_DIR is evaluated at execution time, so updating the variable after defining the alias takes effect immediately.

go_nerv_double
pwd
/home/rei/nerv

With double quotes, $NERV_DIR is fixed to the value at definition time (/home/rei/nerv). Changing the variable later has no effect. Use single quotes to pick up the current variable value at runtime; use double quotes only when you want to hard-code the value at definition time.