Sed is a stream editor: it reads one line of input, performs editing commands, and moves on to the next line. Sed is a companion to ed, Unix's first text editor. Sed is a standard utility.
By far the most common usage of
sed is to perform a simple pattern replacement:
sed -e 's/pattern/replacement/g'
However, sed is Turing-complete; more complex scripts are possible, but quickly become cryptic. A good alternative for tasks that are complicated in sed is awk.