How can I alias `...` to `../..` in Bash?

Question

How can I alias ... to ../.. in Bash?

I am aware that other answers allow alias '...'='cd ../..' but I'd like to be able to address the directory two levels up with other commands, allowing for:

cd ...
ls ...
realpath ...

I have tried alias '...'='../..' but when trying to use this I get the following:

$ alias '...'='../..'
$ type ...
... is aliased to '../..'
$ cd ...
bash: cd: ...: No such file or directory

I'm aware aliases are intended for use with commands. Is there a way to achieve the same functionality for a path in this case?

Answer 1

If switching to zsh is an option, you could use global aliases there for that:

alias -g ...=../..

But in any case that's only expanded when ... is recognised as a full delimited token on its own. It will be expanded in echo ... or echo ...> file or (echo ...) but not in echo .../x or echo ~/... or echo "...").

Normal csh-style aliases, whether it's in bash or zsh are only expanded when in command position or after another alias expansion ending in a blank character. In zsh, though, if you set the autocd option, entering ../.. or another directory as the command name gets turned into cd ../.., so

$ set -o autocd
$ alias ...=../.. ....=../../..
$ ...

Would be a way to cd into ../.., but then again so would alias ...='cd ../..' or ...() cd ../...

A better approach that I've been using for many years is to bind the . key to something that inserts /.. instead of . if what's left of the cursor ends in ..:

magic-dot() {
  if [[ $LBUFFER = (|*[[:blank:]/]).. ]]; then
    repeat ${NUMERIC-1} LBUFFER+=/..
  else
    zle self-insert
  fi
}
zle -N magic-dot
bindkey . magic-dot
bindkey -M isearch . self-insert # restore . in incremental search
                                 # so it doesn't exit isearch there

Then entering ... gets immediately and visually transformed to ../.. and pressing . again changes it to ../../.. and so on. If in emacs mode, .. followed by Alt+4,. makes it ../../../../.. for instance (/.. appended 4 times) using the usual NUMERIC prefix handling.

It used to sometimes get in the way when copy/pasting things that contain ..., but that's no longer a problem now that bracketed paste support has been introduced. To enter a literal ..., you can press Ctrl+v before the third . or use backslashes, quoting or anything that makes so what's left of the cursor ($LBUFFER above) doesn't end in <blanks-or-slash>.. such as .\.., ..\., whatever/'...'...

An intentional limitation of the above is that for instance in sort -o..., the ... is not expanded. Use sort -o ... instead. Same goes for cd '.../***' -> cd ...'/***'. You can change the test above to [[ $LBUFFER = (|*[^.]).. ]] for the ... to be expanded to ../.. in more contexts although that would increase the probability of it being expanded in places you wouldn't like it to.

We can make the numeric argument handling a bit more useful by allowing cd Alt+4. to cd 4 levels up (expand to ../../../..) for instance with:

magic-dot() {
  if (( NUMERIC )) && [[ $LBUFFER = (|*[[:blank:]/:]) ]]; then
    LBUFFER+=..
    (( NUMERIC-- ))
  fi
    
  if [[ $LBUFFER = (|*[[:blank:]/]).. ]]; then
    repeat ${NUMERIC-1} LBUFFER+=/..
  else
    zle self-insert
  fi
}
zle -N magic-dot
bindkey . magic-dot
bindkey -M isearch . self-insert

As mentioned by @Gilles in comment, recent versions of bash have added limited support for editing the line buffer in commands bound to keys, so you could do something similar there with:

insert_before_cursor() {
  # for the equivalent of zsh's repeat $1 LBUFFER+=$2
  local i
  for (( i = 0; i < $1; i++ )); do
    READLINE_LINE=${READLINE_LINE:0:READLINE_POINT}$2${READLINE_LINE:READLINE_POINT}
    (( READLINE_POINT += ${#2} ))
  done
}

magic-dot() {
  (( ${READLINE_ARGUMENT-1} > 0 )) || return
  if [[ -v READLINE_ARGUMENT && ${READLINE_LINE:0:READLINE_POINT} = ?(*[[:blank:]/]) ]]; then
    insert_before_cursor 1 ..
    (( READLINE_ARGUMENT-- ))
  fi

  if [[ ${READLINE_LINE:0:READLINE_POINT} = ?(*[[:blank:]/]).. ]]; then
    insert_before_cursor "${READLINE_ARGUMENT-1}" /..
  else
    insert_before_cursor "${READLINE_ARGUMENT-1}" .
  fi
}
bind -x '".":magic-dot'

# work around a bug in current versions of bash for the numeric
# argument to work properly, that means however that you lose the
# insert-last-argument normally bound to Meta-. (also on Meta-_)
bind -x '"\e.":magic-dot'

You need bash 4.0 or above for $READLINE_LINE (not $READLINE_LINE_BUFFER as misspelled in some of the documentation), and $READLINE_POINT, and 5.2 or above for $READLINE_ARGUMENT, though as noted above it currently doesn't work properly yet.

Answer 2

You can't use aliases for this, aliases are about things you execute, not things you pass to a command as arguments. You could use a variable, but that would mean typing something slightly different. But if you use a short variable name, it can be just two characters:

$ pwd
/home/terdon/foo/bar
$ v="../.."
$ realpath "$v"
/home/terdon

If that works for you, you can add the variable definition to your ~/.profile or ~/.bash_profile files and you will then have access to it in your shell sessions:

v="../.."

Answer 3

There are multiple ways you can reach your goal

METHOD 1: Modify the source code for bash

This method is version specific but is still recommended as its the good way to get things done. What I did is modified builtins/cd.def such that before it checks for absolute path it checks if the first argument is ... if so it sets the dirname to ../.. (sounds like alias only)

STEP 1: Download bash-5.1.16.tar

wget http://ftp.gnu.org/gnu/bash/bash-5.1.16.tar.gz

STEP 2: Fetch & apply the patch bash_5.16_cd_three_dot.patch

tar -xf bash-5.1.16.tar.gz
cd bash-5.1.16
wget https://gist.githubusercontent.com/s0ubhik/6685effe6e46f6a840bb480c5d657933/raw/5736ce64cbb0b009d872c21f40d69c8ee2942b74/bash_5.16_cd_three_dot.patch
patch -p0 < bash_5.16_cd_three_dot.patch

STEP 3: Compile and run

./configure
make
./bash

METHOD 2: Enable autocd in shopt

This methods does not do exactly what you want but i think it is better rather using clever alias techniques

shopt -s autocd

Now if you want to go one directory back just use .. and for two ../..

METHOD 3: Use clever alias

This method works but is not recommend as might be problematic to various scripts the use cd. you may add this to your .bashrc or create a seprate file and then include the file in .bashrc

cd_mod(){
  if [ "$1" == "..." ]; then
    \cd ../../
  else
    \cd $@
  fi
}

alias cd=cd_mod

Answer 4

You can't use alias directly because ... is an argument to cd, but I have seen some people alias cd.. to be cd .., so you could do similar with all of the commands:

alias cd...='cd ../..'

On the other hand...

$ cat ~/mycd 
if [ "$1" = '...' ]
then
  # Use \cd to prevent recursion
  \cd ../..
else
  \cd "$1"
fi

And then

alias cd=". ~/mycd"

Alternatively,

mycd() { if [ "$1" = '...' ]; then \cd ../..; else \cd "$1"; fi; }
alias cd="mycd"