Change Directory Up Faster With Back up Command

2018-03-15 · bash, linux, scripting

Donovan Brown wrote a good article showcasing how you can use a custom PowerShell function to navigate up directories without the need to type multiple cd .. . I found his idea interesting, and it can be a real time saver if you spend a lot of time working in PowerShell.

Unfortunately (or fortunately depends how you see it) nowadays I don’t use PowerShell much — and when I do, my usage is limited to a few PowerCLI commands. I do, however, spend considerable time in the Linux shell, so the natural thing to do was to port Donovan’s idea to a Bash script. The Bash script is going to be different from the PowerShell one, but the concept remains the same.

What do we need?

• A function that takes an integer as an argument.
• A help function that displays a basic help menu when a wrong argument is entered.

The help function:

I like to keep this as simple as possible: one line to describe the argument, and a second line to indicate that this is the help menu:

    function bu_usage () {
       cat <<-EOF
        Usage: bu [N]
                N        Where N is the number of level to move back to. this argument must be an integer.
                h help   displays this basic help menu.
        EOF

I used -EOF to allow indentation, this work better with tabs than with spaces.

The back up function

Now that the help function is out of the way, we can start building the backup function. We know the function takes one argument, and that argument must be an integer:

    function bu () {
        FUNCTIONARG=$1
        # Make sure the provided argument is a positive integer:
        if [[ ! -z "${FUNCTIONARG##*[!0-9]*}" ]]; then
            for i in $(seq 1 $FUNCTIONARG); do
                STRARGMNT+="../"
            done
            CMD="cd ${STRARGMNT}"
            eval $CMD
        else
            bu_usage
        fi
    }

How does it work? The function starts by making sure the argument is a valid integer; if it isn’t, it calls the help function we created earlier. Then, using a sequence of numbers from 1 to the argument, it appends ../ to STRARGMNT on each iteration. When the loop completes, it runs the cd command with all the appended directories. This gives us:

How to use this?

I usually add functions like this to a .functions file in my home directory, which gets sourced by .bash_profile. To source .functions or other dotfiles, add this loop to your .bash_profile (files must be comma-separated):

    for file in ~/.{functions}; do
        [ -r "$file" \] && \[ -f "$file" \] && source "$file";
    done;
    unset file;

Create .functions and add this content to it:

     function bu () {
        function bu_usage () {
           cat <<-EOF
            Usage: bu [N]
                    N        Where N is the number of level to move back to. this argument must be an integer.
                    h help   displays this basic help menu.
            EOF
        }

        # unset variables
        STRARGMNT=""
        FUNCTIONARG=$1

        # Make sure the provided argument is a positive integer:
        if [[ ! -z "${FUNCTIONARG##*[!0-9]*}" ]]; then
            for i in $(seq 1 $FUNCTIONARG); do
                STRARGMNT+="../"
            done
            CMD="cd ${STRARGMNT}"
            eval $CMD
        else
            bu_usage
        fi
    }

This is slightly different from the previous functions we created: the help menu is now a nested function inside the main bu function, and we initialize an empty STRARGMNT to unset the variable each time the function runs.

When you are done, run source .bash_profile — or close and reopen your terminal — for the changes to take effect.

How to run it?

• bu help or bu -h for the help menu
• bu 2 to go two folders up — the equivalent of running cd ../..

You can see bu in action here: