Extracting Directory Paths from File Paths in Bash

Extracting the directory path from a file path is a common task in shell scripting, particularly when working with files and directories. In this tutorial, we will explore how to achieve this using various methods in Bash.

Using `dirname` Command

The dirname command is specifically designed for extracting the directory path from a given file path. It is part of the POSIX standard, making it widely available on most platforms that support Bash. Here’s an example of how to use dirname:

VAR='/home/pax/file.c'
DIR=$(dirname "${VAR}")
echo "${DIR}"

When you run this code, it will output: /home/pax. This demonstrates how dirname can be used to extract the directory path from a file path.

Using Parameter Expansion

Bash also provides parameter expansion, which allows you to manipulate strings without needing external commands. You can use the ${parameter%word} syntax to remove the smallest suffix (in this case, the filename) from the parameter. Here’s how to do it:

VAR='/home/me/mydir/file.c'
DIR=${VAR%/*}
echo "${DIR}"

This will output: /home/me/mydir, which is the directory path extracted from the file path.

Handling Relative Paths and Symbolic Links

When dealing with relative paths or symbolic links, using dirname alone may not yield the desired result. For instance, if you only have a filename without its full path, dirname will simply output . (the current directory). To handle such cases, you can combine readlink with dirname. The readlink -f command resolves symbolic links and returns the absolute path of the file.

fname='txtfile'
echo $(dirname "$fname")                # Output: .
echo $(readlink -f "$fname")            # Output: /home/me/work/txtfile

Then, to get just the directory:

echo $(dirname $(readlink -f "$fname")) # Output: /home/me/work

Checking for Symbolic Links

If you’re working with files that could be symbolic links, it’s a good idea to check for this and handle them accordingly. You can use the [ -h $file ] test to see if a file is a symbolic link.

if [ -h "$file" ]; then
  base=$(dirname $(readlink "$file"))
else
  base=$(dirname "$file")
fi

Getting the Directory of the Current Script

Sometimes, you might need to get the directory path of the current script. This can be achieved using $(dirname $BASH_SOURCE) in combination with cd and pwd to ensure you get an absolute path.

HERE=$(cd $(dirname "$BASH_SOURCE") && pwd)

This sets the HERE variable to the full path of the directory containing the current script, which can be useful for scripting purposes.

Conclusion

Extracting directory paths from file paths in Bash is straightforward and can be accomplished using various methods, including the dirname command, parameter expansion, and combinations of readlink and dirname. Understanding these techniques will help you write more effective shell scripts that handle files and directories with ease.

Using dirname Command