HISTTIMEFORMAT

HISTTIMEFORMAT is an environment variable in Unix-like operating systems that controls the display format of timestamps in the command history. When set, the history command will show the date and time each command was executed, rather than just the command itself. This can be very useful for tracking the sequence of operations and debugging issues.

To set HISTTIMEFORMAT, you typically add it to your shell's configuration file, such as .bashrc or .zshrc. The format string uses the same codes as the `strftime` function, allowing for a high degree of customization. For example, setting HISTTIMEFORMAT="%F %T" would display the date in YYYY-MM-DD format and the time in HH:MM:SS format.

The default behavior without HISTTIMEFORMAT set is to simply list commands sequentially, often with just a sequential number. Enabling HISTTIMEFORMAT provides valuable temporal context for command history, making it a more powerful tool for users who need to analyze their past activity. Common uses include auditing, scripting, and simply remembering when a specific command was run. The variable needs to be exported to be available to sub-processes if necessary, though for interactive shell history, setting it within the shell's configuration file is usually sufficient.