N easy way to insert data/time in front of a log file with just shell scripting

pipescriptingtimestamptopunix-shell

Say I want to monitor memory usage on a java process overnight.

I can do something like

top | grep java > out.log

I will get a log file with a whole bunch of lines.

Is there an easy way to get a data/time inserted in front of each line?

Best Answer

Don't reinvent the wheel. Write the messages to syslog using logger(1), which is supported on just about every Unix flavor. Syslog will take care of the timestamps for you. Your log data will be stored to a system log like /var/log/messages (This is configurable). You don't need to worry about cleaning up the logfiles later on (especially if this job runs forever), because the system logs are automatically rotated by logrotate/newsyslog.

top | grep java | logger -t java_cpuhog

Or, if you really want to write it to your own file. But then you need to clean up the file afterwards:

top | grep java | logger -t java_cpuhog -f /var/log/java-top.log

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