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-like syntax
For all their differences, the two utilities share a similar invocation syntax, both use regular expressions , both read input by default from stdin, and both output to stdout. These are well-behaved UNIX tools, and they work together well. The output from one can be piped into the other, and their combined capabilities give shell scripts some of the power of Perl.