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In Bash, the double pipe || is also known as the OR operator in other programming languages. On the other hand, the single pipe | is known as a pipeline.

In this article, we will see how to use double pipe (also known as OR) and pipelines in Bash scripting. Also, we will see necessary examples and explanations to make the topic easier to understand.

Using double pipes in Bash ||

Putting this double pipe ||between two commands will try to run the first command. If running the first command is unsuccessful, it will execute the second command.

Note that if the first command runs successfully, the second command will not be run.

The general syntax for a double pipe is:

<COMMAND_1> || <COMMAND_2>

In the example shared below, we put two commands together with an OR operator. The code for our example looks like the following:

ls -l || echo "This is a text"

The output of the example shared below shows that it executed only the first command. The output of the above example will look similar to the following:

total 12
-rwxrwxrwx 1 author author   99 Aug  4 14:45 1_Test.txt
-rwxrwxrwx 1 author author  204 Jul 19 15:04 BatchCode.bat
-rwxrwxrwx 1 author author  159 Aug  5 23:04 example.sh
-rwxrwxrwx 1 author author   32 Jul 12 14:05 file1.bat
-rwxrwxrwx 1 author author   33 Jul 12 14:05 file2.bat
-rwxrwxrwx 1 author author   32 Jul 12 14:05 file3.bat
-rwxrwxrwx 1 author author 1330 May 25 00:54 sample.vbs

Using Single Pipe in Bash |

This |is also called piping in Bash. It is used when the output of the first command is used as the input of the second command.

The general syntax of a pipeline is:

<COMMAND_1> | <COMMAND_2>

Let's look at the following example. Suppose we have a Bash script with the following content:

echo "This is the text from the Bash script"

The following example will run the Bash script shared above using an external command. The entire command will look like this:

echo "This is a command" | ./example.sh

Now, after running the above command, you will get the following output:

This is the text from the Bash script

Please note that all the code used in this article is written in Bash. It can only be run in the Linux Shell environment.