Isolating Specific Fields in Data in bash

You need to extract one or more fields from each line of output.

Use cut if there are delimiters you can easily pick out, even if they are different for the beginning and end of the field you need:

Use awk to split on multiples of whitespace, or if you need to rearrange the order of the output fields.

Note the ➝ denotes a tab character in the output. The default is space but you can change that using $OFS:

Use grep -o to display just the part that matched your pattern.

This is particularly handy when you can’t express delimiters in a way that lends itself to the above solutions.
For example, say you need to extract all IP addresses from a file, no matter where they are.

Note we use egrep because of the regular expression (regex), but -o should work with whichever GNU grep flavor you use, but it is probably not supported on non-GNU versions.

Check your documentation.

The possibilities are endless, and we haven’t even scratched the surface here.

This is the very essence of what the Unix toolchain idea is all about.

Take a number of small tools that do one thing well and combine them as needed to solve problems.

Also, the regex we used for IP addresses is naive and could match other things, including invalid addresses.

For a much better pattern, use the Perl Compatible Regular Expressions (PCRE) regex from Mastering Regular Expressions by Jeffrey E. F. Friedl (O’Reilly), if your grep supports -P. Or use Perl.