How can I cd to the previous/next sibling directory?

Question

I often have a project directory layout like this

project
`-- component-a
|   `-- files...
`-- component-b
|   `-- files...
`-- component-c
    `-- files...

I'll usually be working in one of the component directories, because that's where the files are. When I then return to the shell, I'll often simply need to move to a sibling directory, especially when I need to make a few non-scriptable changes to every component. In those cases, I won't even care what the previous sibling directory is that I'll work on, or the next sibling directory.

Can I define a command prev or next that will simply cd me into the previous directory, or next directory (by alphabet or whatever)? Because typing cd ../com<TAB><Arrow keys> all the time is getting a bit old.

Answer 1

Don't use the commandlinefu solution from the other answer: it's unsafe¹ AND inefficient.² Instead, if you are using bash, just use the following functions. To make them persistent, put them into your .bashrc. Note that I use glob order because it's built-in and easy. Typically glob order is alphabetical in most locales though. You'll get an error message if there is no next or previous directory to go to. In particular, you'll see the error if you try to next or prev while in the root directory, /.

## bash and zsh only!
# functions to cd to the next or previous sibling directory, in glob order

prev () {
    # default to current directory if no previous
    local prevdir="./"
    local cwd=${PWD##*/}
    if [[ -z $cwd ]]; then
        # $PWD must be /
        echo 'No previous directory.' >&2
        return 1
    fi
    for x in ../*/; do
        if [[ ${x#../} == ${cwd}/ ]]; then
            # found cwd
            if [[ $prevdir == ./ ]]; then
                echo 'No previous directory.' >&2
                return 1
            fi
            cd "$prevdir"
            return
        fi
        if [[ -d $x ]]; then
            prevdir=$x
        fi
    done
    # Should never get here.
    echo 'Directory not changed.' >&2
    return 1
}

next () {
    local foundcwd=
    local cwd=${PWD##*/}
    if [[ -z $cwd ]]; then
        # $PWD must be /
        echo 'No next directory.' >&2
        return 1
    fi
    for x in ../*/; do
        if [[ -n $foundcwd ]]; then
            if [[ -d $x ]]; then
                cd "$x"
                return
            fi
        elif [[ ${x#../} == ${cwd}/ ]]; then
            foundcwd=1
        fi
    done
    echo 'No next directory.' >&2
    return 1
}

---

^{¹ It doesn't handle all possible directory names. Parsing ls output is never safe.}

^{² cd probably doesn't need to be terribly efficient, but 6 processes is a bit excessive.}

Answer 2

I found a tip over at commandlinefu.com. I'm reposting it here to make it more findable, with an explanation and a next command added while I'm at it.

alias prev='cd ../"$(ls -F .. | grep '/' | grep -B1 -xF "${PWD##*/}/" | head -n 1)"'
alias next='cd ../"$(ls -F .. | grep '/' | grep -A1 -xF "${PWD##*/}/" | tail -n 1)"'

The magic is in the `$(...) block. It pipes a few commands into each other as follows:

ls -F .. |   # list items in parent dir; `-F` requests filetype indicators
grep '/' |   # select the directories (written as  `mydir/`)
grep -B1 -xF "${PWD##*/}/" |   # search for the name of the current directory in the output;
                               # print it and the line preceding it
head -n 1    # the first of those two lines contains the name of the previous sibling