How to Resolve Symbolic Links in a Shell Script

Working with symbolic links (or symlinks) in Unix-like systems can sometimes be tricky, especially when you want to find out the actual path that a symlink points to. If you’re writing a shell script and need to determine the full path of a target after resolving any intermediate symlinks, you’re in the right place. In this blog post, we will break down how to achieve this efficiently.

Understanding the Problem

Imagine you have a situation where you have a symbolic link foo that points to another directory bar. When you run commands like cd foo and pwd, your shell might not reveal the underlying structure clearly, making it hard to derive the full path to the target.

For example:

ls -ld foo bar
drwxr-xr-x   2 greg  greg  68 Aug 11 22:36 bar
lrwxr-xr-x   1 greg  greg   3 Aug 11 22:36 foo -> bar

If you were to execute:

cd foo
pwd

The output would simply be /Users/greg/tmp/foo, which doesn’t really help you if your goal is to discover the actual path foo points to, which is /Users/greg/tmp/bar.

The Solution

Fortunately, there are built-in commands that can help you resolve symlinks in a shell script without needing to delve into C programming. Here’s how to do it:

Using pwd Command

The command pwd -P is used to print the current working directory, resolving all symlinks to provide the absolute path of the target. When you execute:

pwd -P

It will return the full path after resolving any symlinks.

Using getcwd

Another way to accomplish this is by utilizing the getcwd function from the unistd.h library in C. However, if you’re scripting, you can rely on shell commands instead. It’s good practice to know that getcwd has a similar behavior to pwd -P.

Building the Resolve Function

You can wrap these commands into a function to make your work easier. Here’s an example of a simple resolve function in a Bash shell:

resolve() {
    # Use the provided path and resolve it
    local target=$1
    # `readlink -f` follows symlinks, returning the full path
    local full_path=$(readlink -f "$target")
    echo "$full_path"
}

Example Usage

Now, simply call the function with:

resolve "foo"

This will return:

/Users/greg/tmp/bar

This pattern allows you to access the full path of any symlink you’ve encountered in your shell script environment.

Bonus: Resolving User Home Paths

If you also want to resolve home directories using the tilde notation (like ~username), Bash automatically expands these paths in a shell script, so you can combine this with your resolve function seamlessly.

Conclusion

Resolving symbolic links in shell scripts doesn’t have to be complicated. By utilizing the pwd -P command or creating a helper function like resolve that uses readlink, you can effectively determine the full path to your target. This skill is essential for anyone working in a Unix-like environment and makes your scripts much more robust and informative.

Remember, managing symlinks well can save you time and confusion while navigating directory structures or writing complex shell scripts.