Small Shell

A shell-like program that implements a subset feature of bash shell with customized signal handlings.

It is built for practicing C programming and study the following topics:

• process handling (fork, execv, waitpid...)
• change directory (chdir)
• signal handling (sigaction)
• input and output redirect (dup2)

Start the program

compile: gcc -std=c99 -o smallsh smallsh.c

run: ./smallsh

Functionality

General syntax:

command [arg1 arg2 ...] [< input_file] [> output_file] [&]

The command promopt

• colon : symbol is the prompt for each command line
• supports input and ouput rediect with < and >
• supports background process with &
• supports commenting with #
• supports variable expansion, $$ will be replaced with current process PID

Built-in commands

• exit: exit small shell
• cd: works like UNIX cd command
• status: prints out either the exit status or the terminating signal of the last foreground process ran by your shell.

Other commands

• All unix commands works as usual.

SIGINT and SIGTSTP

SIGINT

CTRL-C sends SIGINT to the parent shell process and all its child processes

• Parent process will ignore SIGINT
• Background process will ignore SIGINT
• Child process will terminate itself when received SIGINT

SIGTSTP

CTRL-Z sends SIGTSTP to the parent shell process and all its child processes

• Child process will ignore SIGTSTP
• Background process will ignore SIGTSTP
• SIGTSTP will toggle the shell to "foreground-only mode", meaning all subsequent commands with & will be ignored. (Will therefore run in the foreground). Can toggle it back with CTRL-Z.