Internal and external cmd

[siva19185]

what is Internal and external command in linux....

can anyone give some examples..

[GNU-Fan]

Hello,

Linux is a kernel providing an interface to the hardware and assigning the resources (like processor time and memory) to the applications. Over this interface the programs (called userspace applications) can talk to the kernel when they need the system to do something for them.

You as an user interact with the userspace applications. One very generic application is a command line interpreter (CLI), also called a shell. The program 'bash' is a widely available example for a shell. This shell is usually the first program that is automatically started when you log in on any terminal (window). Most of the time you start other programs from this shell.

For example, there is an executable called 'echo' that prints out a line of text. When you ask your shell to start it, the shell in turn tells Linux to load it into memory and grant it some processor time and some memory. This program usually resides on the harddisc in the /bin/ folder.
As it has to be loaded from there it is called an external command.

But as the 'echo' program is so famous and therefore used very frequently, the developers of Bash considered it a good idea to built it in the bash binary. Now you do not have to rely on the program laying on your hard disc but when you type 'echo', bash already knows what to do without loading another program. Therefore this 'echo' facility can be called a 'builtin', or 'internal' command.

For more examples, type 'man builtins'.