How to Extract Filename from Absolute Path in Bash
Last updated
Last updated
Whenever dealing with absolute paths, we will come across situations where we just need the name of the file. What do we do then? Definitely, we can use the available tools in Bash like awk.
We also have tailor-made tools whose sole purpose is to extract the final component in the file path. Basename is one such command-line utility. Another popular technique is the parameter expansion for removing the directory and trailing suffix from file names. In this tutorial, we will also examine the drawbacks of the different approaches and look at a real-world problem.
The obvious question is why to extract? We have multiple reasons to do so.
To rename the file or extension - We may want to extract the filename or extension to rename it with a new name or extension.
To have a new file name with the timestamp - We generally have log files in Linux with the same file name and extension. But the file name gets a suffix as the timestamp.
We will focus on three of the most common ways by which we can extract the filename with its extension in Bash.
With Bash we can employ many utilities to extract the filename and the extension from the given file path. But, why go to such great lengths when we have a tailor-made tool whose sole purpose is to fetch the final component in the file path. is a command-line tool for removing the directory and trailing suffix from file names.
Example:
Basename is a simple tool to implement. All it does is finds the last path separator (/). It displays whatever is present after that. As we can notice, the command is totally unbiased when it comes to files or directories. Its job is to simply give us the information after the final slash.
To make the command interpret more than one path, we supply -a. We can also give the --multiple flag. It is used to achieve the same. Then comes a list of files, each separated by a space.
Example:
In our example, we will get the name of the two files with their respective extensions, sample.txt and sample1.cfg from their respective paths. These two will appear in separate lines.
To separate these outputs with NULL rather than a newline we have to pass the -z flag along with it.
Example:
One major drawback of this command is that it will extract the filename with the extension. We cannot use it just to extract the extension or the directory path.
Example:
The above example can be generalized as follows:
This trims the longest match from the beginning till the pattern. It displays whatever is after the pattern. The only drawback is that we have to use a variable since this is a parameter expansion.
In our example, we have used the regex (*) as the pattern. In the pattern we have also added the path separator (/). It will look for all the characters till the last slash (/) and trim it. Hence, we will get the characters after the final path separator. The only drawback here is that we cannot use the string directory. There is no other option but to store the string in a variable.
The awk command was developed by Aho, Weinberger, and Kernighan and gets its name from their initials. It is a powerful, widely used Linux tool that lets us process and manipulate data. It also supports performing arithmetic operations. We can also take its help to extract the filename with its extension.
Example:
In this example, we have taken a variable to hold the entire file path. We are free to supply that string directly to the echo command. We pipe the result of this echo command so that Bash can send it as an input to the awk command. The -F option available with the awk command acts as the field separator. We have built the regular expression for the awk statement in such a way that the string dissociates into two halves from the final slash (/). $NF ensures that Bash only prints the last column in the record.
As we have learned different ways of fetching the name of the file, we can look at an example that prompts the user to provide the complete path of the file. The script checks the existence of the file. It then asks the user to provide the directory where he wants to keep a backup of this file with the same name and extension.
Example:
#!/bin/bash read -p "Enter the filename with it's complete path: " fpath if [ ! -f "$fpath" ]then echo "Invalid file. Please check the input."else read -p "Enter the complete path where you want to copy it: " fdir if [ ! -d "$fdir" ] then echo "Invalid new directory. Please check the input."else fname=`basename $fpath` cp $fpath ${fdir}/${fname} fi fi
1. The script begins by prompting the user to enter the filename with its complete path. It does it by employing the read command. The user input is stored in the fpath variable.
2. The script verifies the existence of the file specified in fpath using the -f test condition. If the file doesn't exist, it prints "Invalid file. Please check the input."
3. If the file exists, the script again prompts the user to enter the complete path of the destination directory where the file should be copied to. The entered value is stored in the fdir variable.
4. It then checks if the directory specified by fdir does not exist using the -d test condition. If the directory doesn't exist, it prints "Invalid new directory. Please check the input."
5. If both the file and the directory exist, the script uses the basename command to extract the filename from the given file path and stores it in the fname variable.
6. Finally, the cp command is used to copy the file specified by fpath to the destination directory ${fdir}/${fname}.
We can fetch the file name along with its extension from the absolute file path.
Basename is a simple enough command that can be used with certain limitations to pull out the filename.
With parameter expansions, we can extract parts of a variable and name of the file
We have seen the use of certain readily available powerful tools like awk.
Bash has an interesting feature named parameter expansion. With , we can extract parts of a variable. It has a unique syntax. This won't be available with other programming languages.
