grep Options

Plain grep is useful, but a few options make it far smarter.

Ignore case: grep -i

By default grep is case-sensitive: Error and error are different. The -i option makes the search case-insensitive:

grep -i error system.log

This matches error, Error, ERROR, and any mix.

Count matches: grep -c

The -c option prints just the number of matching lines, not the lines themselves:

grep -c warning system.log

3

Invert the match: grep -v

The -v option flips the search: it prints lines that do NOT contain the word:

grep -v info system.log

This hides every info line and shows everything else.

Show line numbers: grep -n

The -n option puts the line number in front of each match:

grep -n error system.log

5:error: sensor 3 offline

Options combine, just like with ls: grep -in error system.log is case-insensitive and numbered.

Mission: Shift-End Log Summary

Before handing off to the night crew, you need to prepare a summary of system.log: how many warnings were logged, what non-routine events occurred, and a copy filed for the next shift.

1. Count how many lines contain warning, just the number, not the lines themselves.
2. Print every line that does not contain info: the non-routine events.
3. Print the error lines with a line number in front of each, so the night crew can jump straight to them.
4. Create a folder called handoff and copy system.log into it as night-brief.log.

Expected result

You see the warning count, the filtered non-routine lines, the numbered error line, and a copy of the log waiting in handoff.