Internal vs External command

[caophuong2012]

UNIX commands are classified into two types:

Internal command (like cd, fg):

• Built into the shell

• No process needs to be spawned to executing it

External command (like ls, cat):

• Not built into the shell
• New process are spawned
• The command has corresponding script like /usr/bin/ls or /usr/bin/cat

To check a command is internal or external:

$ type cd
cd is a shell builtin

$ type ls
ls is an alias for ls --color=tty

Internal vs External command: The big difference between the two types is performance, then we should try to use internal command if it's available.