Shell

RUNNING THE SHELL

run make to generate the executable

run ./a.out to run the shell

run exit to exit the shell

FEATURES

Foreground processes

• The shell waits for the current process to execute

Background processes

• Use '&' at the end of any command to invoke a background process
• The process will then run in the background and when exited, a message will be displayed

ls command

• ls takes arguments as flags (as -) and directories (as )
• It lists the files of the directory mentioned. If no directory is mentioned, it lists the files in the current directory
• ls - lists in alphabetical order
• ls -l - long list
• ls -a - display hidden files
• ls -al/-la - long list including hidden files

cd command

• cd <absolute path> - goes to absolute path
• cd - goes to ~/
• cd ~/<pathname> - goes to ~/
• cd .. - goes to previous directory
• cd . - stays in the same directory

echo command

• echo - prints empty line
• echo text - prints text

pwd command

• pwd - prints absolute path of current directory

pinfo command

• pinfo - prints process info of the shell
• pinfo <pid> - prints process info of given pid

Environment variables

• The shell inherits environment variables from the parent
• getenv - used to get the username

exit command

• exit - exit the shell. The shell exits only when quit is typed

Redirection

• Output of running one (or more) commands must be redirected to a file.

Set unset environment variables

• The shell inherits environment variables from the parent
• setenv var [value] - ​ If environment variable ​ var does not exist, then it will create it.
• unsetenv var - ​it will destroy the environment variable ​ var.

User define command

• jobs - prints a list of all currently running jobs along with their pid.
• ​ kjob <jobNumber> <signalNumber> - takes the job id of a running job and sends a signal value to that process.
• ​​ fg <jobNumber> -brings a running or a stopped background job with given job number to foreground. ​​ bg <jobNumber> - changes a stopped background job to a running background job.
• ​ overkill - ​ kills all background process at once.
• ​ CTRL-Z ​- It should change the status of currently running job to stop, and push it in background process
• ​ CTRL-C ​ : It should cause a SIGINT signal to be sent to the current foreground job of your shell​ .
• ​ ​ Cronjob ​ : executes a particular command in fixed time interval for a certain period.