Bash Script – Check if file has read permissions

To check if a file is writable in bash, in other words if the file has write permissions for current user, use -w option.

The syntax of the boolean expression to check if a file is writeable or not is given below.

[ -w path/to/file ]

replace path/to/file with the actual path to file, whose write permissions you need to check.

The expression returns a value of true if the file is present and has write permission for current user, or a false if the file does not have write permissions.

Examples

For the sake of examples, we check the write permissions of two files shown below.

sh-3.2# ls -lr
total 32
-rw-rw-rw-@ 1 tutorialkart  staff    42 Feb  4 16:55 sample.txt
-rwxrwxrwx@ 1 tutorialkart  staff   136 Feb  5 07:51 example.sh
-r--r--r--  1 tutorialkart  staff     0 Feb  4 17:24 data.txt

If you observe the permissions for these files,

  • sample.txt has write permissions for all users.
  • data.txt has only read permissions, but no write permissions.
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1. Check if File is Writable – sample.txt

In the following example, we shall use -w option to check if the file sample.txt is writable.

Bash Script File

#!/bin/bash

filename="sample.txt"

if [ -w "$filename" ];
then
	echo "$filename is writable."
else
	echo "$filename is not writable."
fi

Bash Version: GNU bash, version 5.2.15(1)-release (aarch64-apple-darwin22.1.0)

Run this script file in a Terminal, and you shall see the following output, provided you have the files mentioned in your system with the same permissions.

Output

2. Check if File is Writable – data.txt

In the following example, we shall use -w option to check if the file data.txt is writable. Since data.txt has no right permissions, else block must execute.

Bash Script File

#!/bin/bash

file="data.txt"

if [ -w "$file" ]
then
	echo "$file is writable."
else
	echo "$file is not writable."
fi

Bash Version: GNU bash, version 5.2.15(1)-release (aarch64-apple-darwin22.1.0)

Run this script file in a Terminal, and you shall see the following output, provided you have the data.txt with the same permissions mentioned above.

Output

sh-3.2# bash example.sh 
data.txt is not writable.

Conclusion

In this Bash Tutorial, we learned how to check if specified file is writable or not.