Implementation of a shell using the C programming language. It includes the major functions of a shell where it prints the working directory, parses user input/command line, and executes the given command line with the given arguments.
- Execute standard UNIX commands
- I/O redirection (< and >)
- Displays and repeatedly prompts user after command and its execution
- Parse Command Line: Provides a way to parse input that allows redirection and command execution with arguments.
Clone the repository and compile source code using GCC
git clone [(https://github.com/ViperKelly/TechShell.git)]
cd techshell
gcc -o techshell techshell.c
Alternative is to download the repository as a zip and do the last two commands as seen.
Run the shell through terminal
./techshell
- ls: Listing. includes arguments
-l, -lh, etc - Echo: allows for printing/writing of strings
- Redirect: Output of commands correctly create or append to a file and gives/prints the output. Input to commands is allowed ex. 'wc -l < ps.out'
- Most basic UNIX commands See typescript
All known problems
- As of now does not support piping or AND for multi command usage ('||', '&&')
- Simple error handles. More in depth errors are not expected to be shown.
#BreakDown
- Simply a driver that unless told to exit repeatedly runs the created functions to print working directory, prompt user input of command line, and execute command.
- This is not in main but is a main function. Create a struct for the ShellCommand. (this includes giving command a command, arguments, redirect, input/output files.)
- Takes the current working directory detected by the unistd.h library with getcwd
- Using stdio and fgets take in a user input from the command line. Returns this input.
- This function is a struct creation of the ShellCommand
- Take in the user input from Command Prompt
- Using the string library the tokenize function strtok() went through the user input and tokenized it at each space.
- This tokenized string got put into the arguments array and also the first token was put as the command.
- Each token was compared using strcmp to check for quotes to start a in quote function that would put all things inside quotes as one token.
- Each token was also compared for redirection calls (<, >, >>) and took the next token as the file and set it to the corresponding variable from the struct. An integere value 1 or 2 was given for each input redirection to check for append or overwrite
- the created command struct was returned
- Takes in the command object created in parsing
- checks to see if the command gathered is cd and handles change directory. if '..' is the argument move back a directory. For any other changing of directory gather all the arguments that aren't the command and combine them (makes sure to get any directories with spaces) then change directory.
- For other command executions fork the program
- In the child process call the redirection function and then execute the command with its arguments
- Redirection program takes in the command object and checks to see if input or output files exist. Using freopen the files will be open and then read or written to.
- If these files exist then for input redirection open the file with read and read that to standard input.
- For output redirection check the redirect interger for if it is an append or overwrite call and then open the file with w for overwrite or a for append. This also creates a file if it doesn't exist yet.
- A remove character function was created that loops through a string (token in our case) to get rid of any undesired characters. This is used to guarantee that quotes and the redirection symbols are excluded from outputs
- For Error Handling very basic print error statements were used to print that an error occured. The print statement tells where that error happened.
Any commented feedback is welcome. Requests for code changes will be thoroughly looked at and tested.
Public Free License
[email protected] (504) 654 7575