What is the difference between `|` and `||` in Linux?

In Linux, while these two symbols look similar, they serve completely different purposes. Think of the single pipe as a connector and the double pipe as a decision maker.

Here is the breakdown:

1. The Single Pipe (|) - "The Connector"

The pipe is used to pass data from one command to another.

• Meaning: Takes the output of the first command and uses it as the input for the second.
• Key usage: Combining tools to process data.
• Example:

  ls -l | cowsay

  All the file details from ls -l are sent into the cow's mouth.

2. The Double Pipe (||) - "The Backup Plan"

The double pipe is a logical operator used for conditional execution.

• Meaning: Run the second command ONLY IF the first command fails (returns an error).
• Key usage: Handling errors or providing a fallback.
• Example:

  cd folder_that_doesnt_exist || echo "Directory not found!"

  Since the cd command will fail, the echo command will run to tell you there was an error.

Comparison Table

One more for your toolkit: &&

To complete the set, Linux also uses && (Double Ampersand).

• This means "Run the second command ONLY IF the first one succeeds."
• Example: make && echo "Build successful!"

In summary:

• Use | when you want to process data.
• Use || when you want to check for errors.