This is a very brief introduction to the sed and awk text processing utilities. We will deal with only a few basic commands here, but that will suffice for understanding simple sed and awk constructs within shell scripts.
sed: a non-interactive text file editor
awk: a field-oriented pattern processing language with a C-style syntax
For all their differences, the two utilities share a similar
invocation syntax, use regular
expressions , read input by default
from stdin, and output to
stdout. These are well-behaved UNIX tools,
and they work together well. The output from one can be piped
to the other, and their combined capabilities give shell scripts
some of the power of Perl.
One important difference between the utilities is that while shell scripts can easily pass arguments to sed, it is more cumbersome for awk (see Example 36.5, “ A shell wrapper around another awk script” and Example 28.2, “Passing an indirect reference to awk”).