What is a heredoc?

A heredoc (here-document) is a feature in Unix-like operating systems that allows you to create a block of text that can be used as input for a command. It enables you to specify a multi-line string directly in your script or command line without needing to use multiple echo statements or other methods.

Syntax

The basic syntax for a heredoc is as follows:

command <<EOF
line 1
line 2
line 3
EOF

In this example:

• command is the command that will receive the input.
• <<EOF indicates the start of the heredoc, where EOF is a delimiter that you can choose (it can be any string).
• The lines between the start and end delimiters are treated as input to the command.

Example

Here’s a simple example using cat to display a multi-line string:

cat <<EOF
This is line 1.
This is line 2.
This is line 3.
EOF

When you run this, it will output:

This is line 1.
This is line 2.
This is line 3.

Use Cases

Heredocs are often used in scripts for:

• Providing multi-line input to commands.
• Creating configuration files or scripts dynamically.
• Writing documentation or comments within scripts.

Conclusion

Heredocs are a powerful feature for handling multi-line strings in shell scripting, making it easier to manage input without cluttering your code with multiple commands.