Unix-Shell-in-C

Basic linux shell made using C

Commands Implemented

Internal Commands

• cd
• echo
• pwd
• history
• exit

External Commands

• ls
• date
• mkdir
• cat
• rm

Detailed Description

Internal commands are handled directly by shell. For each external command I have made a .c file and used fork() and execl() to implement those functions. I am reading input through readline.

Errors handled:

1)waitpid(): On error, -1 is returned. 2)If process id returned by fork is <0, means there was error in fork. 3)invalid arguments

Commands

• cd:

  • -P use the physical directory structure without following symbolic links
  • --help gives description of cd
  • errors: too many arguments, no such directory found, error opening help file

• echo:

  • -n do not output the trailing newline
  • -E disable interpretation of backslash escapes (default)

• history:

  • -c clear
  • -d remove a particular entry

• pwd:

  • -P print the physical directory, without any symbolic links
  • --help help gives description of pwd
  • errors: too many arguments, error in getting current directory, error opening help file

• exit

• ls:

  • -1 display in different lines
  • -a display all files, including hidden
  • errors: could not open current directory, invalid argument

• cat(takes multiple arguments)

  • -n number the lines
  • -E add '$' to the end of line
  • errors: error opening file, file doesnt exist

• date

  • -u shows Universal time(GMT)
  • -R shows date in RFC 5322 format
  • errors: invalid command

• rm

  • -f ignore nonexistent files and arguments, never prompt
  • -i prompt before every removal
  • errors: can't remove as its a directory, file doesn't exist

• mkdir

  • -m set file mode (as in chmod)
  • -v print a message when directory created
  • errors: file already exists, error while creating(errno)

Assumptions

• echo prints backslash characters and quotes too.
• rm -i when prompts, 1 means yes and any other int means no.
• any other options or commands except those mentioned above are considered to be invalid.