Permanent Bash aliases

Sep 3, 2014

This post will introduce a handy little Bash tip. I created it over a year ago but many other people have already done similar things.

Bash aliases are incredibly convenient. If, for some reason, you don't already use them then you should read this tutorial.

Anyway, on to the function:

mkalias() {
  # Flatten arguments into one string
  local full_string=$*

  # Extract the first and last parts
  local alias_name=${full_string%%=*}
  local alias_result=${full_string#*=}

  # Construct the new command
  local alias_command="alias $alias_name='$alias_result'"

  # Execute the command, if successful then print 
  # out the alias and add it to ~/.bash_aliases
  eval "$alias_command" && \
  alias "$alias_name" | tee -a "$HOME/.bash_aliases"

This allows you to create a "permanent" alias which gets added to your ~/.bash_aliases file. It has a few other features. It prints out the alias (as interpreted by Bash) so you can check that nothing went wrong. It also allows you to omit quotes in many circumstances.

mkalias hello=echo hello world  # Quotes optional
#=> alias hello='echo hello world'

#=> hello world


mkalias cdrc=cd $RC_DIR  # Probably wrong
#=> alias cdrc='cd /home/david/sync/dotfiles'

mkalias cdrc='cd $RC_DIR'  # Should be quoted
#=> alias cdrc='cd $RC_DIR'

mkalias lsl='ls | less'  # Must be quoted
#=> alias lsl='ls | less'

bash  # Open new shell

hello  # Alias is remembered
#=> hello world

The function can still fail if you use the wrong syntax (e.g. by putting whitespace around the = character). It would also be nice to find a way to share aliases between already running Bash instances.

One final tip, if you create an alias that "overwrites" another command, you can precede it with a backslash to run the original command.

mkalias ls=ls -CF
#=> alias ls='ls -CF'

ls  # Notice trailing slashes on directories
#=> CNAME       _config.yml  _posts/  _site/  feed.xml  index.html
#=>   _drafts/     _layouts/  _sass/   css/    images/

\ls  # Regular ls behaviour
#=> CNAME      _config.yml  _posts   _site  feed.xml  index.html
#=>  _drafts      _layouts   _sass    css    images