20 C
Jaipur
Thursday, January 21, 2021

Bash if -e and -s and other file test operators in Linux

Must read

File Test Operators are used in Linux to check and verify attributes of files like ownership or if they are a symlink. Every Test operator has a specific purpose. The most important operators are -e and -s. In this article, you will learn to test files using the if statement followed by some important test operators in Linux.

In this article we will cover the following test operators:

  • If -e test operator
  • If -s test operator
  • If -d test operator
  • If -h test operator
  • If -r test operator
  • If -O test operator

Use of if -e Operator

The key aim of using the if-e test operator in Centos 8 is to verify if the specific file resides in the directory or not. So if you want to verify the existence of a file using if-e, you have to follow the steps below:

Create two new files with the names  Test.txt  and FileTestOperators.sh respectively. Extension .sh belongs to the bash file. You may create both in the home directory directly, or with the following command:

$ touch Test.txt
$ touch FileTestOperators.sh

If you want to authenticate whether or not the file is created, use the following command:

$ ls -l Test.txt

Create operators file

You can see both the files are created in the home directory.

Files in file explorer

Open the file FileTestOperators.sh and write down the script in it as shown in the below image. We have initialized a variable file and passed the Test.txt file as a value to it. In the If statement, we have the -e operator used to confirm the existence of file Test.txt using variable file.

Script 1

Run the below-mentioned command to check the existence of the file:

$ bash FileTestOperators.sh

As the file exists in the directory, so the output will be True.

run script 1

Use of if -s Operator

The purpose of using the if-s test operator in Centos 8 is to verify if the specified file exists and is empty or not. So if you want to verify it using if-e, you have to follow the steps below:

We will be using the same files with a minor change in the file FileTestOperators.sh.  You just have to change the -s operator instead of -e in the if statement.

script 2

Run the below-mentioned command to check whether the file is empty or not:

$ bash FileTestOperators.sh

As the file is empty, so the output generated by the -s operator is False

Run script 2

Now you have to add some text in the file Test.txt to alter the result, as shown in the below image.

Test file

Again run the below-mentioned command:

$ bash FileTestOperators.sh

As the file is not empty this time, so the output generated by the -s operator will be True as shown in the image.

Run test againAdvertisement

You can also use the following two commands to verify that file is empty:

$ cat Test.txt
$ file Test.txt

File is empty

Use of if -d Operator

The aim of using the if-d test operator in Centos 8 is to verify that the specific file is itself a directory or not. So if you want to check it using if-d, you should follow the below-mentioned steps:

Here, again we are using the same both files with a slight change in the FileTestOperators.sh bash file.  We have to change the -s operator with the -d operator in the if statement as shown in the below image.

test script 4

So, runs the below-mentioned command to check whether the file is a directory or not:

$ bash FileTestOperators.sh

As we know the Test.txt file is not a directory that is why the -d operator outputs False Test.txt is not a directory as shown in the below image.

run test

Use of if -h Operator

The if-h test operator is used to check whether the file is a symbolic (soft) link or not. So if you want to verify the existence of a file using if-h, you have to go through the following steps:

Create a new file with the name SymbolicFile.sh. You may create it in the home directory directly, or with the following command:Advertisement

$ touch SymbolicFile.sh

file test

You can see the SymbolicFile.sh file in the home directory as shown in the below image.

Symbolic link

You can list all the directories and files using the ls command. You can see the SymbolicFile.sh file is also listed as shown in the image.

$ ls –l

symlink

Create a symbolic link using a simple link command. In this command, -s refers to a soft link, SymbolicFile.sh is a file whose link will be created, and NewSymbolicFile.sh is a symbolic link.

$ ln -s SymbolicFile.sh NewSymbolicFile.sh

Test for symlinks

Again list all the directories and files. You can see a soft link has been created.

Run test

So, again we are using FileTestOperators.sh bash file with a slight change.Change -d operator with -h operator in the if statement. This time we have to change a file name as well. We have to use a file that is a symbolic link itself e.g. NewSymbolicFile.sh.

Check for symlinks

You can see both files in the below image.

Files

Now run the below command:

$ bash FileTestOperators.sh

As we know the NewSymbolicFile.sh file is a symbolic link, that is why the -h operator outputs True NewSymbolicFile.sh is a symbolic link as shown in the below image.

Run symlink test

Use of if -r Operator

The if -r test operator is used to check the readability of the file e.g. the file is readable or not. So if you want to check it using if-r, you have to follow these steps:

Again,  we are using Test.txt and FileTestOperators.sh bash file with a slight change. Change -h operator with -r operator in the if statement and assign Test.txt file as a value to variable file.

Check if file is readable

Now run the below command:

$ bash FileTestOperators.sh

As we know that the Test.txt file is readable so the -r operator outputs True! Test.txt is readable.

Run readability test

Note: Use -w and -x operators respectively to verify whether the file is writable and executable or not.

Use of if -O Operator

The purpose of the if -O test operator is used to check whether the file is owned by a current user or not. So to verify it using if-O, you have to go through these steps:

Again, we are using Test.txt and FileTestOperators.sh bash file with a little change.  Change -r operator with -O operator in the if statement and assign Test.txt file as a value to variable file.

Ownership test in bash

Now run the below command:

$ bash FileTestOperators.sh

As we know that the Test.txt file is already owned by the current user so the -O operator outputs True Test.txt is owned by a current user.

Run test

Conclusion

In this article, you have learned about the most important and different file test operators and their working in Centos 8.  I hope you are now able to create files, checking the existence of files, checking the readability of files, checking ownership of files, and making soft links. Users can feel themself at ease after following this article thoroughly.

Source link

- Advertisement -

More articles

LEAVE A REPLY

Please enter your comment!
Please enter your name here

Latest article