rsh

rsh (rishav's shell) is a basic shell developed as part of the CSE-1 course (Monsoon 2019) at IIIT Hyderabad.

Notable features include piping, redirection and proper job control with foreground and background job support. Also present is history recall and tab completion for filenames. A variety of builtins have also been implemented (see src/builtin.c).

Build

rsh uses the meson build system. To install, either apt install meson or brew install meson.

We also need the readline library. Either brew install readline or apt install libreadline-dev.

Then:

meson build
ninja -C build

The executable can be found at build/rsh.

Basic Features

• semi-colon delimited list of jobs: cd /; pwd; ls
• i/o redirection: sort < in.txt > out.txt
• piping: cat in.txt | sort | wc -l > out.txt
• start jobs in the background: sleep 500 &
• job suspension with CTRL-Z, along with job control using fg and bg
• view job list: jobs
• history recall and file-name completion

Bonus

• cronjob -c command -p cycle -t duration: run command every cycle seconds for duration seconds asynchronously
• setenv and unsetenv
• pinfo: show process info
• kjob: send signal to some arbitrary PID
• overkill: kill all background jobs

Components

• builtin.c: matches the input against the list of builtins; currently cd, pwd, echo, ls, pinfo, nightswatch, dirty, interrupts, history, quit, jobs, setenv, unsetenv, fg, bg, kjob, overkill, cronjob.
• cronjob.c: implements the cronjob builtin
• env.c: implements the setenv and unsetenv builtins
• history.c: responsible for loading the history list from disk, maintaining it in memory, and persisting to file on exit
• ls.c: implements the ls builtin. The -l and -a options are implemented
• nightswatch.c: implements the nightswatch builtin; supports the dirty and interrupts sub-commands
• pinfo.c: implements the pinfo builtin to fetch process information. Not supported on macOS due to lack of a procfs
• external.c: runs external commands (non-builtins); responsible for putting newly created processes into their own groups and handling terminal control
• interpret.c: checks if the input matches a builtin, otherwise delegates to the external handler
• main.c: runs the main REPL loop. The main shell state data structure is also defined in main.h. Also responsible for initializing the shell; handling SIGCHLD, and saving the existing term attributes for restoring later
• parse.c: tokenizes and parses the input line. Supports semicolon delimited commands, optionally ampersand terminated to indicate a background job
• prompt.c: generates the prompt
• util.c: has utility functions for operating on the job table, etc.
• kill.c: implements the kjob and overkill builtins

Known Bugs

• Input of the form foo>out.txt or foo> out.txt is not parsed correctly.

License

See LICENSE.txt