Part A deals with parsing a shell script within a small subset of the standard POSIX shell grammar. Refer to the specification listed below for more details. Part B concerns building the execution model for the shell. In Part C we parallelized the execution of shell commands with no dependencies. The goal was to maintain 100% accuracy but not necessarily 100% parallelization.

• 1A) Shell script parser

  • Detects invalid grammar
  • Ignores comments
  • Supports detection for subshells
  • Print out a diagnostic with the '-p'flag

• 1B) Execution model

  • I/O redirections handled (within the specification)
  • Subshells executed appropriately

• 1C) Parallelization model

  • Turn on parallelization with the '-t' flag

• 1A) Shell script parser

  • Cannot handle append operator '>>'
  • Doesn't support the tokens '((' or '))'
  • Memory leaks galore

• 1B) Execution model

  • Doesn't support control flow statements such as 'if', 'while', etc.
  • Possibly not closing all opened file descriptors
  • Doesn't support the shell directive 'exec' properly
  • Will not properly handle commands like 'cd' or 'rm'

• 1C) Parallelization model

  • Doesn't parallelize within each command tree, only amongst command trees
  • Shell prompt may return before all shell commands print out their results
  • More memory leaks introduced

1. Clone this repository using 'git clone https://github.com/stanwayl/time-travel-shell'
2. Create an executable 'timetrash' by running 'make'
3. Run shell using './timetrash [OPTION] script.sh' within the directory

If we don't care too much about memory, unify all the different node structures into a single one with all needed fields. Then don't need to worry about type conversions and data structures can just hold a single type of node. Also easier to just go through them all and free them when done.

http://cs.ucla.edu/classes/spring14/cs111/assign/lab1.html