Книга: Fedora™ Unleashed, 2008 edition

Printing the Last Lines of a File with tail

Printing the Last Lines of a File with tail

If you want to watch a log file as it is written to, or want to monitor a user's actions as they are occurring, you need to be able to track log files as they change. In these situations, you need the tail command, which prints the last few lines of a file and updates as new lines are added. This command tells tail to print the last few lines of /var/log/httpd/access_log, the Apache hit log:

$ tail /var/log/httpd/access_log

To get tail to remain running and update as the file changes, add the -f parameter (which means "follow"):

$ tail -f /var/log/httpd/access_log

You can tie the lifespan of a tail call to follow the existence of a process by specifying the --pid parameter. When you do this, tail continues to follow the file you asked for until it sees that the process (identified by PID) is no longer running, at which point tail stops tailing.

If you specify multiple files on the command line, tail follows both, printing file headers whenever the input source changes. Press Ctrl+C to terminate tail when in follow mode.

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