Update File Timestamps

The touch command is a fundamental utility in Unix-like operating systems used to change file timestamps. It can be used to create new empty files or to update the access and modification times of existing files. This tool is invaluable for developers and system administrators who need precise control over file metadata.

Using Touch to Set Specific Timestamps

You can specify a particular date and time to set for a file's modification timestamp. The -d option allows for flexible time string parsing, making it easy to set timestamps relative to the current time or to absolute dates.

# To change a file's modification time:
touch -d <time> <file>
touch -d 12am <file>
touch -d "yesterday 6am" <file>
touch -d "2 days ago 10:00" <file>
touch -d "tomorrow 04:00" <file>

Copying Timestamps with Reference Files

A powerful feature of the touch command is its ability to copy the timestamp from one file to another. This is achieved using the -r option, which is particularly useful for synchronizing timestamps or for testing scenarios where exact time replication is needed.

# To put the timestamp of a file on another:
touch -r <refrence-file> <target-file>

Understanding File Timestamps

File timestamps typically include access time (atime), modification time (mtime), and change time (ctime). The touch command primarily manipulates mtime and atime. Understanding these timestamps is crucial for various tasks, including file synchronization, backup strategies, and debugging.

Further Resources

• Linux touch man page
• MDN Web Docs: Date Object (for understanding time formats)