Shellfish

Fall 2014

Runs on Linux/macOS

Compile with make, run with ./shell Exit with exit, quit, or Ctrl-D at the start of a line

Basic Features

• Execute multiple commands per line, separated by ;
  • Trim excess white space
  • Ignore consecutive semicolons rather than returning a syntax error
• Basic file redirection: <, >, >>
• Basic piping: |
• Checked for memory leaks: Valgrind

Todo

Enhancements

---

• Tilde expansion: ~ is interchangeable with user's $HOME directory
• Color prompt:
  • Username, hostname, current working directory
• Better redirection and piping:
  • cmd < in > out
  • cmd > out1 flag1 flag2
  • cmd1 | cmd2 | cmd3
  • cmd1 | cmd2 > out1
  • <<, <<<, redirection for STDERR and other file descriptors
• Handle EOF (Ctrl-D)
• Handle SIGINT (Ctrl-C)
  • Re-print the prompt
• Command history & navigation
• Directory history & navigation (cd -)
• Wildcard *
• Tab completion: for files and commands
• Logic operators: &&, ||, !
• Background processes: &

Bugs & Minor Enhancements

---

• Fix: Segfault when exiting with EOF after using ~ expansion, redirection, or pipes
• Allow redirect and pipe symbols to be adjacent to commands or flags (not separated by space)
• Allow tilde expansion to work in conjunction with redirection e.g. ls ~ > out

Function Headers

shell.h

• static void sigHandler(int signo)
  • Allows SIGINT to interrupt the shell's commands rather than the shell itself
• void redirect()
  • Handles the redirection (calls to dup2) of file descriptors
• void safe_exec()
  • Executes the command in argv with execvp and safely frees all allocated memory before exiting
• void executePipe(int pipeIndex)
  • A new child executes the first command from argv with safe_exec, writing into the pipe
  • The parent executes the rest of the command with executeMisc while reading out of the pipe
• void executeMisc()
  • Searches for any pipes | in global var argv and calls executePipe if it finds one. If not, it redirects if parseInput found a redirect symbol and finally calls safe_exec
• void execute()
  • Handles exit (or quit) and cd commands, otherwise forking and the new child calls executeMisc
• char ** parseInput(char *input, char *delim)
  • Returns a dynamically allocated char **argv of input arguments separated by delim and trimmed of whitespace and semicolons
  • Redirect symbols and the first argument afterwards are not added to argv. They set booleans redir_out and/or redir_in to true and the file (if valid) is stored in a global variable.
• void shell()
  • Continuously loops through the shell procedures: reading and parsing user input and then executing the commands
  • If the return value of fgets is null, the user has sent an EOF at the start of a line and the shell exits normally