shell.md

Building a simple shell

This assignment is based on the shell homework from the MIT's operating systems course (see, https://pdos.csail.mit.edu/6.828/2014/index.html)

This program has to be implemented in the C or C++ programming languages and executed by the xterm terminal emulator. The source code sh.c and the grammar sh_grammar.y are provided as a basis for implementing it. This program contains a parser that recognises shell commands such as the following:

ls > y
cat < y | sort | uniq | wc > y1
cat y1
rm y1
ls |  sort | uniq | wc
rm y
> out.txt ls
> out.txt
< in.txt > out.txt sort

This program has to implement the following functionality:

• Execution of the built-in command cd.
• Execution of simple commands such as ls.
• Execution of commands as foreground or background process groups. For example, ls -l, ./myprog&, etc.
• Redirection of commands standard input and standard output. For example, echo "hello" > x.txt, sort < in.txt, ls -l > myfile, etc.
• Execution of pipelines of commands such as ls | sort | uniq | wc.
• To handle SIGHUP, SIGINT, and SIGQUIT signals so that they are sent to the right process groups.