Linux Pocket Guide, 2nd Edition

File Location

find	Locate files in a directory hierarchy.
xargs	Process a list of located files (and much more).
locate	Create an index of files, and search the index for string.
which	Locate executables in your search path (command).
type	Locate executables in your search path (bash built-in).
whereis	Locate executables, documentation, and source files.

Linux systems can contain hundreds of thousands of files easily. How can you find a particular file when you need to? The first step is to organize your files logically into directories in some thoughtful manner, but there are several other ways to find files, depending on what you’re looking for.

For finding any file, find is a brute-force program that slogs file-by-file through a directory hierarchy to locate a target. locate is much faster, searching through a prebuilt index that you generate as needed. (Some distros generate the index nightly by default.)

For finding programs, the which and type commands check all directories in your shell search path. type is built into the bash shell (and therefore available only when you’re running bash), while which is a program (normally /usr/bin/which); type is faster and can detect shell aliases.^[12] In contrast, whereis examines a known set of directories, rather than your search path.

^[12] The tcsh shell performs some trickery to make which detect aliases.