Tuesday, April 01, 2003

Backtracking with bash

I was working with linux quite a bit today, and frequently changing between directories, when I wondered if there was a way to go back to the directory I was in previously.

Turns out there is a way:

 cd ~-
So if I was doing something like this:
[pete@bigred /]$ cd /etc
[pete@bigred etc]$ cd /usr/local
[pete@bigred local]$ cd ~-
[pete@bigred etc]$ pwd
If you want to create a command so you don't have to type ~- you can create an alias:
alias cdb='cd ~-'
This ~- thing works great if you only need to go back one directory, but what if you wanted to go back two directories. Continuing the last code sample:
[pete@bigred etc]$ cd ~-
[pete@bigred local]$ cd ~-
[pete@bigred etc]$ pwd
We are back to /etc and not / our starting point. What I want is something that keeps a history of the directories I've been to.

It turns out that the Bash (the "Bourne again shell") has a directory stack builtin. Three command line tools for manipulating the stack are avaliable dirs, pushd, and popd. More info about the directory stack in bash here.

If we pushd a directory onto the directory stack, we can retreive the top of the stack using dirs +1. I tried setting up some aliases to get it to work the way I wanted:

alias cdd='pushd'
alias cdb='cd `dirs +1`'
Those worked a bit, but I ran into a lot of problems, especially when in the home directory. Also when you run pushd, popd, or dirs it always prints the contents of the stack, I don't know how to suppress that. So I figured I would post it here, and see if anyone can come up with a solution, or if anyone knows of a better way of going about this.

Isn't it funny how software developers will spend hours of time trying to save a few seconds of their future time.