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.