Shulou(Shulou.com)06/01 Report--

This article introduces the relevant knowledge of "what are the Linux system commands". In the operation of actual cases, many people will encounter such a dilemma. Then let the editor lead you to learn how to deal with these situations. I hope you can read it carefully and be able to achieve something!

Linux commands are divided into internal commands and external commands:

Internal commands are called into memory when the system is started, and are resident in memory, so the execution efficiency is high.

The external command is the software function of the system, and the user only reads the memory from the hard disk when needed.

Type can be used to determine whether a command is a built-in command

Type: usage: type [- afptP] name [name. ]

[root@linuxeye ~] # type type

Type is a shell builtin

[root@linuxeye] # type-p type

[root@linuxeye] # type-t type

Builtin

[root@linuxeye ~] # type type

Type is a shell builtin

[root@linuxeye] # type-t type

Builtin

[root@linuxeye ~] # type pwd

Pwd is a shell builtin

[root@linuxeye ~] # type whiptail

Whiptail is / usr/bin/whiptail

[root@linuxeye] # type-t whiptail

File

Enable can not only view internal commands, but also determine whether they are internal commands.

[root@linuxeye ~] # enable-a # View internal commands

[root@linuxeye ~] # enable whiptail # non-internal command

-bash: enable: whiptail: not a shell builtin

[root@linuxeye ~] # enable pwd # is an internal command

Internal command user input when the system call rate is fast, not built-in commands, the system will read the environment variable file .bash _ profile, / etc/profile to find the PATH path.

Then when you mention the invocation of the command, some historical commands will exist in the hash table after they have been used, and the call to the command will be such a process when you type the command again.

The invocation of the hash-- "built-in command--" PATH command should actually be such a process.

[root@linuxeye ~] # type pwd

Pwd is a shell builtin

[root@linuxeye ~] # type cat

Cat is / usr/bin/cat

[root@linuxeye ~] # ls linuxeye*

Linuxeye.pem linuxeye.txt

[root@linuxeye ~] # cat linuxeye.txt

Linuxeye

[root@linuxeye ~] # hash-l # displays the hash table

Builtin hash-p / usr/bin/cat cat

Builtin hash-p / usr/bin/ls ls

[root@linuxeye ~] # type cat

Cat is hashed (/ usr/bin/cat)

[root@linuxeye ~] # hash-r # clear the hash table

[root@linuxeye ~] # type cat

Cat is / usr/bin/cat

As can be seen from the above operation. The hash table does not hold system built-in commands.

This is the end of the content of "what Linux system commands". Thank you for reading. If you want to know more about the industry, you can follow the website, the editor will output more high-quality practical articles for you!

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.