prefix - adds hostname, time information, or more to lines from stdin (or read from files)
% tail -f /var/log/some.log | prefix -host -timestamp
tails a file, showing each line with a hostname and a timestamp like. So if we were tailing a growing file with lines like:
OK: System operational Warning: Disk bandwidth saturated
we would get real-time output like:
host.example.com 2013-10-13 16:51:26 OK: System operational host.example.com 2013-10-13 16:55:47 Warning: Disk bandwidth saturated host.example.com 2013-10-13 16:55:49 Warning: Things are wonky: disks spinning backwards host.example.com 2013-10-13 16:55:50 Error: Data read wackbards host.example.com 2013-10-13 16:56:10 OK: Spacetime reversal complete
Note that the hostname (host.example.com) and the date have been prepended to the lines from the file
The prefix program also supports adding arbitrary text, current time to the microsecond, time elapsed since invocation, time since last line output, adding text at the end instead of the beginning of the line, and more.
A text filter that prepends (or appends) data to lines read from stdin or named files, and echos them to stdout
add any particular string you like. For example
% ./some_program | prefix -text="TestRun17:" -utime > logfile.txt
The above example would prefix each line output from some_program with the time and the text 'TestRun17:' (without the quotes).
Add a timestamp to each line
% ls -l | prefix -timestamp
Add a timestamp, showing fractions of a second to each line
% ls -l | prefix -utimestamp
Add the hostname to each line
Don't put a space between the original line read and the data added to each line
Show all added data at end of line, not start of line
% echo "abc" | prefix -suffix -text=:Run17:
(note how the added text is now at the end of the line) whereas:
% echo "abc" | prefix -text=:Run17:
Add the time since the prefix program was started to each line
Add time elapsed since last line seen. Shows fractional time.
This can be useful when tailing logfiles or output of programs and you want to see which lines take longer or shorter to output.
Show --elapsedstamp and --diffstamp times in seconds, and never in other units (like minutes or microseconds, for example)
Show each original line read in single quotes
Josh Rabinowitz <joshr>