How to shrink or extend the size of a file in Linux?

The truncate command is used to shrink or extend the size of a file to a specified size in Linux. Unlike deletion commands, truncate cannot remove files but can modify their contents and size. When reducing file size, if the specified size is smaller than the actual size, the extra data will be permanently lost.

Syntax

The general syntax of the truncate command is as follows:

truncate OPTION... FILE...

Options

Brief description of options available in the truncate command:

Common Use Cases

Emptying a File

To remove all contents of a file and set its size to zero bytes:

truncate -s 0 file.txt

This command empties the file completely while preserving the file itself.

Creating Files with Specific Size

If the specified file doesn't exist, truncate will create a new file with the given size:

truncate -s 200K file.txt

This creates a 200KB file named file.txt in the current directory.

Preventing File Creation

To prevent creating new files when they don't exist, use the -c option:

truncate -c -s 200K file.txt

If file.txt doesn't exist, no new file will be created and the command will fail silently.

Examples

Extending File Size

To extend a file to 1MB (padding with null bytes):

truncate -s 1M document.txt

Using Reference File

To make one file the same size as another:

truncate -r reference.txt target.txt

Checking Available Options

To view all available options and usage information:

truncate --help

Size Specifications

The truncate command supports various size units:

Conclusion

The truncate command is a powerful tool for file size management in Linux. It can efficiently shrink files by removing excess data or extend them by padding with null bytes. Always use caution when shrinking files as data loss is permanent and irreversible.