How to exclude results from grep

Sometimes you may wish to further filter grep output, such as in the following situation:

# zfs get all | grep compressratio

backup01         compressratio         1.23x                  –
backup01         refcompressratio      1.00x                  –
backup01/data    compressratio         1.50x                  –
backup01/data    refcompressratio      1.50x                  –
backup01/photos  compressratio         1.05x                  –
backup01/photos  refcompressratio      1.05x                  –

Here we only really want to see the compressratio results, not the refcompressratio. We can pipe the grep output to another grep command, this time inverting the results with the -v switch.

# zfs get all | grep compressratio | grep -v refcompressratio

backup01         compressratio         1.21x                  –
backup01/data    compressratio         1.50x                  –
backup01/photos  compressratio         1.05x                  –

This excludes any line containing refcompressratio, making the results easier to read. This is particularly helpful when you have a large number of results from grep.