Linux Learning Notes 14--commands which and Whereis

We often find a file in Linux, but do not know where to put it, you can use some of the following commands to search:
Which view the location of the executable file.
Whereis View the location of the file.
Locate to view the file location with the database.
Find actual search hard disk query file name.

The purpose of the which command is to search for the location of a system command in the path specified by the path variable, 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.

1. Command format:

which executable file name

2. Command function:

The which instruction searches for the location of a system command in the path specified by the path variable, and returns the first search result.

3. Command parameters:

-n Specifies the length of the file name, which must be greater than or equal to the longest file name in all files.

-P is the same as the-n parameter, but the path to the file is included here.

-W Specifies the width of the field at the output.

-V Display version information

4. Usage examples:

Example 1: Finding files, displaying command paths

Command:

Which lsmod

Output:

[email protected] ~]# which PWD

/bin/pwd

[email protected] ~]# which useradd

/usr/sbin/useradd

[Email protected] ~]#

Description

Which is to search for a running file based on the directory within the PATH variable configured by the user! Therefore, the different PATH configuration content found the command of course not the same!

Example 2: Use which to find which

Command:

which which

Output:

[email protected] ~]# which which

Alias Which= ' Alias | /usr/bin/which--tty-only--read-alias--show-dot--show-tilde '

/usr/bin/which

[Email protected] ~]#

Description

There will be two which, one of which is alias. This is called the "command alias", meaning that the input which will wait for the next sequence of commands!

Example 3: Find the CD command

Command:

which CD

Output:

Description

CD is a common command can not find Ah! Why is it? This is because the CD is a command built in bash! But which default is to find the PATH within the standard directory, so of course, must not find!

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The Whereis command can only be used for program name searches, and only binary files (parameter-B), man description file (parameter-m), and source code file (parameter-s) are searched. If the argument is omitted, all information is returned.

Whereis looks very fast compared to find, because the Linux system records all the files in the system in a single database file, and when you use Whereis and the locate described below, the data is looked up from the database, not like the Find command, By traversing the hard drive to find, the efficiency will naturally be very high.

However, the database file is not updated in real time and is updated once a week by default, so when we use Whereis and locate to find files, we sometimes find data that has been deleted, or just created the file, but cannot find it because the database file is not updated.

1. Command format:

Whereis [-BMSU] [BMS directory name-f] File name

2. Command function:

The Whereis command locates the location of the executable file, the source code file, and the Help file in the file system. The properties of these files should belong to the original code, binary files, or Help files. The Whereis program also has the ability to search for source code, specify alternate search paths, and search for unusual items.

3. Command parameters:

-B locates the executable file.

-M locate the help file.

-S Locate the source code file.

-U searches the default path for files other than executables, source code files, and Help files.

-b Specifies the path to the search executable file.

-m specifies the path to the search Help file.

-s Specifies the path of the search source code file.

4. Usage examples:

Example 1: Find files related to * * files

Command:

Whereis SVN

Output:

[Email protected] ~]# Whereis Tomcat

Tomcat:

[Email protected] ~]# Whereis SVN

SVN:/usr/bin/svn/usr/local/svn/usr/share/man/man1/svn.1.gz

Description

Tomcat is not installed, can not find out, SVN installation found a lot of related files

Example 2: Only binary files are found

Command:

Whereis-b SVN

Output:

[Email protected] ~]# Whereis-b SVN

SVN:/USR/BIN/SVN/USR/LOCAL/SVN

[Email protected] ~]# whereis-m SVN

SVN:/usr/share/man/man1/svn.1.gz

[Email protected] ~]# whereis-s SVN

Svn:

[Email protected] ~]#

Description

Whereis-m SVN to find the description document path, Whereis-s svn for source files.

Linux Learning Notes 14--commands which and Whereis