When a rules matches, an action is taken. There are currently four supported actions:

  • line
  • match
  • blank
  • suppress

The line Action

The line action instructs Clog to color the entire line. This makes the whole line more visible. An example might be to color a line in a log file if that line reports a critical error.

The match Action

The match action instructs clog to only color the matching pattern and not the entire line. This make individual keywords more visible. An example might be to highlight simply an error code, or server name.

The blank Action

The blank action causes a blank line to be written both before and after the matching line. This is another form of emphasis.

The suppress Action

The suppress action causes the whole line to be removed from the output. You will not see a suppressed line at all. This is useful for stripping out noise from a log file.


Here is a default rule set that includes all the different actions. The first rule will make any line completely blue if it contains the word 'blue'. The second rule colors the word 'red' red. The third puts blank lines around any line containing the word 'emphasize'. The fourth rule suppresses any line containing the word 'ignore'.

Here is a sample file that triggers every rule, so we should see the actions of all rules taken. Can you predict what will happen?

Here is the output:

This shows rules precedence also - the second rule finds the word 'red' in the blue line.