Able to delete part of the system log files on Mac OSX El Capitan based on a time period?

The files in /var/log/ are owned by root so you’ll have to be able to use sudo from Terminal, i.e., be a local admin.

Once you have that, you can use the sed command to perform the actual task with something like this

sudo sed -i -e s/^.*09:[00-59]:[00-59].*$//g /var/log/someLogFile.log

To further explain:

• sudo to give you write access to files owned by root
• -i Edits the file in-place
• -e Tells sed you’ll be using a regex command following this option
• s/^.*09:[00-59]:[00-59].*$//g initiates the sed substitution command for any line logged for all of 09:00:00 to 09:59:59 with nothing (2 consecutive slashes), for all lines (/g)