问题
I'm a newbie to process and thread management. My Shell should understand PATH environment variable. It can be set and modified. It runs in two ways -interactive & batch mode. Shell is capable of taking more than one job like ls;ps;wc file;cal. I want to get my hands dirty on signals too. So I should handle ^K , ^c as well.
I know I will have to use execs, forks and pipes but just can't get started.
回答1:
All the unix shells are open-source - so a good place to start may be to read the code.
If you're looking for a good starter article on the subject try Writing Your Own Shell from the Linux Gazette.
Another good starting point is to take a look at the source code of mini-shell just because its one of the smallest to get your head round.
回答2:
Your main loop is:
- read a line (use
fgets(3)for a simple shell,readline(3)for a fancy one) - parse the command
- fork and execute the pipelines
To parse the command, there are two common choices. Write a recursive descent parser or use yacc(1) to generate one. It's a lot easier to bang out an initial parser using yacc, but you can totally get stuck debugging it and it really wants to be context-free. I prefer recursive descent but just about everyone else in the world prefers using yacc. (Technically, bison.) If the shell is really really simple, like a homework shell, yacc may be overkill.
To do the lexical analysis you can also roll your own or use flex.
You won't need to use any threads.
回答3:
Many of the Unix books that describe the main system calls also implement a shell to illustrate how and why you might use the various calls. Stevens and Rochkind are two such books:
W Richard Stevens, Stephen A Rago Advanced Programming in the Unix Environment, 3rd Edn
Marc J Rochkind Advanced Unix Programming, 2nd Edn
来源：https://stackoverflow.com/questions/1500004/how-can-i-implement-my-own-basic-unix-shell-in-c