How Linux finds the path to a command

Linux, we often use CD, Grep,vi and other commands, and sometimes we have to find out where these commands are, how to do it?

Linux has 2 commands to complete this function:which, Whereis

Which is used to view when

The path to the command to execute before.

Whereis is used to view a command or the path of a file.

The principle of the which command: in the path specified by the path variable, search for the location of a system command and return the first search result. That is, with the which command, you can see whether a system command exists, and the command that executes exactly which location.

Examples of use of the which command:

$ which grep

Whereis command principle: only search for program name, and only binary file (parameter-B), man description file (parameter-m) and source code file (parameter-s). If the argument is omitted, all information is returned.

Examples of use of the Whereis command:

$ whereis grep

Here is an example to illustrate. Join your Linux system with multiple versions of Java installed. If you knock the command "java-version" directly at the command line, you will get a result. But, do you know which path Java is executing? If you want to know, you can use the which command:

which Java

Returns the location of the first Java in the path, where the Java command is executed by default

If you use the command: Whereis Java

Then you will get a lot of results because this command lists all the paths that contain Java (whether files or folders).

How Linux finds the path to a command