Like other editors, Emacs has commands for searching for occurrences of a string. The principal search command is unusual in that it is incremental; it begins to search before you have finished typing the search string. There are also nonincremental search commands more like those of other editors.
Besides the usual replace-string command that finds all
occurrences of one string and replaces them with another, Emacs has a
more flexible replacement command called query-replace, which
asks interactively which occurrences to replace. There are also
commands to find and operate on all matches for a pattern.
You can also search multiple files under control of a tags
table (see Tags Search) or through the Dired A command
(see Operating on Files), or ask the grep program to do it
(see Grep Searching).