Bash for Each File in a Directory
Last updated
Last updated
In this tutorial, we will explore the versatility of Bash for loops and learn how to effectively iterate over files in a directory. By using a wildcard expression, such as an asterisk (*), we can effortlessly loop through all the entries in a directory and perform file manipulation tasks.
We will walk through practical examples that demonstrate the power of Bash for loops, including displaying file extensions and renaming files with specific extensions.
Bash for loop when used with the wildcard expression asterisk (*) will loop through all the entries of the directory and in each step store that entry in a variable.
Here’s the syntax:
The Bash for loops has made the task of looping through the contents of any directory effortless. We can consider this as iterating over elements of the array. Let us understand this process in detail.
The first thing needed is to create a directory. Let us create a directory named "MyDir'' using the mkdir command. Then we need to enter this directory using the cd command.
We create files in this directory as follows:
Now that we have everything ready, we can easily loop through the files present in this directory using the for loop with the wildcard asterisk (*).
Example:
#!/bin/bashfor file in *doecho $file - `head -1 $file`done
We have used the wildcard character asterisk (*) to build the for loop expression. This is the beauty of Bash. It allows regular expressions in its loops. The asterisk informs the for loop to consider every single file in the directory.
The variable "file" is the iterator which will pick up the entries of the directory one by one. It then prints the name of the file followed by the first line in that file using the head command.
In the following example, the script prompts the user for the directory path . After checking its existence it lists the extensions of all the files present.
Example:
#!/bin/bash read -p "Enter the directory path: " dpath if [ ! -d "$dpath" ]then echo "Invalid directory. Please check the input."else contentsOfDir=`ls`for content in $contentsOfDirdo if [ -d $content ] then echo $content is a directory and will not have any extension else ext=`echo ${content#*.}` echo "$content has extension: "$ext fidonefi
2. The script verifies if the user input is a directory or not using the -d test condition on the variable dpath. If the path is non-existent, it prints "Invalid directory path. Please check the input."
3. If the file exists, the script fetches all the contents of that directory and stores it in the variable contentsofDir using the backticks technique.
4. The script runs a for loop for all the contents present in that directory. The for loop iterator is named content.
5. In every iteration, the script checks if the content is a file or directory. If it is a directory, it displays that the current value of the iterator is a directory and will not have any extension.
6. If it is a file (not a directory), the script will extract the extension using the parameter expansion and store the result in the ext variable.
7. For each iteration, it will finally print the name of the file and the extension it has.
The script prompts the user for the directory path. After checking its existence it asks the user to provide the old and new extension. Based on that it rename those files with the new extensions
Example:
#!/bin/bash read -p "Enter the directory path: " dpath if [ ! -d "$dpath" ]then echo "Invalid directory. Please check the input."else read -p "Enter the extension you want to replace: " oldExt read -p "Enter the new extension you want: " newExt for entry in $dpath/* do if [ ! -d $entry ] then ext=`echo ${entry#*.}` if [ "$ext" = "$oldExt" ] then filename=`basename -s $ext $entry` mv $entry ${filename}${newExt} echo ${filename}${newExt} in ${dpath} is renamed to ${filename}${newExt} fi fi donefi
1. The script begins by using the read command to prompt the user to enter the directory path. The entered value is stored in the variable named dpath.
2. The script checks if the value present in that variable is a directory or not. It uses the -d test condition in the if expression. If the directory structure is non-existent, it prints "Invalid directory path. Please check the input."
3. If the file exists, the script prompts the user to enter the old extension that has to be renamed. This response is stored in the oldExt variable.
4. The script looks for the new extension from the user. This response is held by the newExt variable.
5. The script runs a for loop for every entry in the provided path. The iterator is named as "entry" and is assigned the task of looping through all the contents of the directory one at a time.
6. The script first verifies that the input is a file or directory in each for loop run. It is ignored and the iterator points to the next entry, if it is a directory,
7. The script pulls out the extension of the file and stores it in the variable named "ext", if it is a file.
8. The script then does a comparison of the value present in the oldExt and the ext variables.
10. It then moves the filename present in the iterator to ${filename}${newExt}.
11. By the end of the script, all the files will get renamed with the new extension.
We learned how the for loop works with a . Now, we will look at a couple of real-world problems where we will write and understand bash scripts to bring this theory to practice.
1. The execution of the script starts by prompting the user to enter the directory path. This is done by the and it stores the response in the variable named dpath.
9. Only if they match, the script extracts the name of the file using the .
