A custom shell I made using C

• Run "make" in the SinShell directory.
• Then, run "./sin" to run the shell
• Type "exit" to exit the shell

• pwd
  • "pwd" will print the absolute path to the present working directory
  • pwd is implemented in "pwd.c' and "pwd.h"
• echo [string]
  • "echo [string]" will print the string in the terminal after removing extra white spaces (spaces-' ', and tabs-'\t')
  • echo is implemented in "echo.c" and "echo.h"
• cd [directory path]
  • "cd [directory path]" will change the present working directory of the terminal
  • "cd" or "cd ~" will change the present working directory to the home directory of the shell
  • cd is implemented in "cd.c" and "cd.h"
• ls [flags] [directory path]
  • "ls" lists all files present in the current working directory in alphabetical order
  • "ls [directory path]" lists all files present in the directory specified by [directory path] in alphabetical order
  • Possible flags: -l (displays extra information regarding files), -a (display all files, including hidden files), -al/-la (displays extra information regarding all files, including hidden files)
  • ls can also handle multiple [directory path]s, in which case it will list the files of all provided directories
  • the order in which the flags and [directory path]s are provided is inconsequential to the working of ls
  • ls is implemented in "ls.c" and "ls.h"
• pinfo [pid]
  • "pinfo" prints information regarding the process corresponding to the shell beingg executed
  • "pinfo [pid]" prints information regarding the process corresponding to the [pid] provided
  • pinfo makes use of the /proc/[pid]/stat and /proc/[pid]/exe files to obtain information regarding ongoing processes
  • To get process status and memory, it is assumed that they are the 3rd and 23rd elements in /proc/[pid]/stat, this is consistent with BASH shell
  • pinfo is implemented in "pinfo.c" and "pinfo.h"
• history [number of commands]
  • "history" lists the 10 most recently executed commands (incuding the history command)
  • "history [number of commands]` lists the [number of commands] most recently executed commands
  • if [number of commands] is entered as a value greater than 20, an error will be printed
  • if number of executed commands is less than requested number of commands, the maximum number of recorded commands will be printed
  • the executed commands are stored in "hist_info.txt", and if "hist_info.txt" does not exist then it will be created as a part of the command
  • history is implemented in "history.c" and "history.h"
• setenv var [value]
  • "setenv var [value]" can be used to create/modify environment variables.
  • If there is no environment variable of the name var, then a new environment variable is created and is gien the value [value].
  • If there already exists an envorinment variable with the name var, then the value of that environment variable is updated so that it will be [value].
  • setenv is implemented in "env.c" and "env.h".
• unsetenv var
  • "unsetenv var" can be used to remove the environment variable with name var.
  • unsetenv is implemented in 'env.c" and "env.h".
• jobs
  • "jobs" prints information regarding all running and/or stopped background processes.
  • "jobs" prints the job number, execution status, executed command, and pid of each running or stopped background process.
  • jobs is implemented in "jobs.c" and "jobs.h".
• kjob <job number> <signal number>
  • "kjob " sends a signal defined by to the job defined by .
  • kjob can be used to kill specific background processes or influence their execution status.
  • kjob is implemented in "kjob.c" and "kjob.h".
• fg
• bg
• overkill
  • "overkill" kills all present background processes.
  • overkill is executed in "overkill.c" and "overkill.h".
• quit
  • "quit" quits the shell
  • "Ctrl+D" will also quit the shell
  • quit is implemented in "main.c" directly

• foreground
  • handles foreground processes other than the implemented commands using execvp
  • foreground is implemented in "foreground.c" and "foreground.h"
• background
  • handles background processes other than the implemented commands using execvp
  • printf info (name, pid, and exit status) of background processes when terminated
  • background is implemented in "background.c" and "background.h"

• prompt
  • prompt is run at the start of the shell loop and displays the username, system name and current directory.
  • prompt is implemented in "prompt.c" and "prompt.h"

• Ctrl+C
  • Ctrl+C will interrupt any running foreground process with the SIGINT signal.
  • Ctrl+C will NOT interrupt the shell itself and will not exit the shell.
• Ctrl+Z
  • Ctrl+Z will push any running foreground process to the background and will change it's state from running to stopped.

• ';' separated commands
  • SinShell is equipped to execute multiple ';' separated commands
• Handling extra white space
  • SinShell is equipped to handle extra spaces(' ') and tabs('\t') in commands
• I/O Redirection
  • SinShell supports I/O redirection using '>', '>>' and '<'.
  • '>' overwrites the output file and creates the output file (with permissions 644) if it doesn't exist.
  • '>>' appends to the output file and creates the output file (with permissions 644) if it doesn't exist.
  • '<' redirects a given input file as the input (STDIN) of a certain command.
• Piping
  • SinShell suppports piping between commands using the '|' character.
  • if two commands are run with a pipe in between them (i.e. "<command 1> | <command 2>"), then the STDOUT of command 1 is piped/redirected to the STDIN of command 2.
  • SinShell also supports the use of both piping and redirection simultaneously. For any command, I/O redirection has a higher priority than redirection using piping.