Internal Command
Internal commands are the commands that are executed
directly by the shell. These commands will not have a separate process. You can’t
find these commands in PATH directories in system because these are built in shell
command. echo is an external command and if you try to find its path it will
show shell built in.
$ type echo
echo is a shell builtin
when you run echo the system will not search in PATH
location, it will execute it from shell builtin commands that are stored in
some separate file.
External Command
External commands are the commands that are executed by the kernel.
These commands will have a process id running for it. External Command existed
in any PATH directory like /bin, /usr/bin etc. like ls, sed, mv. These commands
having independent existence in /bin, /usr/bin, or any other directory. External commands
paths can be found using type command
$ type ls
ls is /bin/ls
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