One difficulty when working at a command line is navigating between directories, particularly between locations with long paths. There are several ways to mitigate this. One of the simplest is using cd - to return to the previous directory. Another is to use pushd and popd. Still another is to set the CDPATH variable.
qcd function
This post presents another approach that could be used instead of or in addition to the ones mentioned above. The book Efficient Linux at the Command Line by Daniel Barrett contains a function called qcd (quick change directory) that will cd to any of a list of commonly used directories. The function is essentially a big case statement taking a key and going to a corresponding directory.
qcd () {
case "$1" in
work)
cd $HOME/Work/Projects/Web/src/include
;;
recipes)
cd $HOME/Family/Cooking/Recipes
;;
…
esac
pwd
}
So, for example, qcd work will take you to the directory ~/…/include.
Barrett adds one more line after the definition of the qcd function:
complete -W "work recipes …" qcd
This turns on tab completion for the script using the bash builtin function complete. You use this function implicitly when you use tab completion with shell utilities. You can call it as above to add the same command completion to your own functions. So, for example, with the code above, a user could type
qcd w TAB
instead of cd work.
Improvements
The book says “Store the function in a shell configuration file such as $HOME/.bashrc … source it, and it’s ready to run.” I’d like to make two comments about this.
First, it’s important that qcd is a function and not a script. Scripts run in a subshell, so running a cd command in a script changes your working directory while the script is running. But when the script finishes, the subshell exits, and the working directory is just as it was before running the script.
Second, if you use this function you’ll edit it frequently as you think of new directories to add. I’d rather not put it in my .bashrc file for that reason. Also, maybe I’d like to use it from a bash shell on a Linux box and from zshell on a Mac. So instead of putting the definition of qcd in my .bashrc file, I put it in a file qcd.sh and source that file from my .bashrc file.
When you add a new key and directory to the qcd script, you need to also add the key to the call to complete, otherwise you’ll be in the awkward situation of tab completion working for some directories but not others. It would be possible to write a fancier shell script that would fix this problem.
Generating qcd
My knowledge of shell scripting is minimal, and I’d like to keep it that way. If I need to do something complicated, I don’t do it in a shell script. So I wrote a Python script to generate the qcd.sh file from a dictionary of keys and directories. Someone fluent in shell scripting would find this unnecessarily complicated. To each his own.
By the way, if you’re going to write a Python script, why not just write a Python script and be done with it rather than write a Python script to generate a shell script? For the same reason qcd is a function: cd inside a Python script will only change the working directory while the script is running. There is probably some way around this, but I didn’t want to take the time to figure it out.
Related posts
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