working of bash shell
 

can any one tell me how does bash help in executing the command echo and kill.how does the shell checks whether the command is builtin command or not. plz tell the complete procedure for both commands.

Without inspecting the bash source code it's hard to know but it probably has a list of its own built-ins and, when it is given a command to execute without a path (without a leading ~, ./ or /) it consults that list.

Bash shell forks a child process in order to execute any command including 'echo' or 'kill' whatever.

The child process i.e. 'echo' or 'kill' whatever dies automatically when it completes its execution !

I see u are posting all your assignment questions one by one for us to solve ?????????

Try reading this:

http://tldp.org/LDP/abs/html/internal.html

AIUI built-ins do not require fork exec and that is one of the reasons for having built-ins such as echo when perfectly good external commands like /bin/echo already exist. From the link (my emphasis) "A builtin is a command contained within the Bash tool set, literally built in. This is either for performance reasons -- builtins execute faster than external commands, which usually require forking off [1] a separate process"

If these are homework questions (and they could well be) they are unusual ones or strangely re-cast.

sir actually i m not posting all my assignment here. we were given an assignmment on working of shell. its our intrest to know extra in this field

then its best to understand the source.

Thanks for the confirmation :)

I thought as much. Your questions go beyond homework (they would be unfairly hard questions for homework when first learning bash). Nice that you are curious and want to fully understand :)

Several of your questions relate (indirectly) to *n*x processes. Your curiosity and hunger for deeper understanding would be rewarded by learning about processes. Here are some links. Best to start with the first because it explains processes as seen from the shell that you are already learning about.

• http://www.faqs.org/docs/linux_intro/sect_04_01.html
• http://www.linux-tutorial.info/modul...ntent&pageid=3
• http://www.linux-tutorial.info/modul...tent&pageid=83

thanks for the enlightenment !

Of course, what will be the use of builtin commands if shell still had to fork a process for them ! They are there for the speed !

True -- and some of them because they would not work as external commands, the cd built-in for example. Can you figure out why an external cd command would not work (it's process-related)?

cd cannot work as an external command because an external command creates a child process, and a process cannot affect the environment of its parent (shell in this case). :)