During 42 school, I realized operating system projects including the creation of a Unix system Command Line Interpreter in C language. This project, 42sh, is the accomplishment of a dozen other projects carried out in a logical sequence which is validated in several weeks to a few months each.

The use of C libraries was limited, and the compilation rules and programming standards were strict. Our team of 3 students chose Bash 5.0 as the reference shell and developed the following functionalities:

• Execution of commands with their parameters and management of $PATH
• Error handling and return value
• Complete command line editing
• Dynamic and contextual completion of commands, built-ins, files and variables
• Inhibitors :
  • ’ single quote
  • ” double quote
  • \ backslash
• Logical operators :
  • &&
  • ||
• Redirect operators :
  • >
  • >>
  • <
  • <<
  • <<<
  • >&
  • <&
  • |
• The separator ;
• Management of all signals
• Program suspension by the operator & as well as the built-ins :
  • jobs
  • fg
  • bg
• Integration of internal variables with :
  • creation with syntax var=value
  • display with buit-in set
  • revocation with the built-in unset (internal and environment variable)
  • export with built-in export
• Alias support with built-ins alias and unalias
• Optimizing the search for binaries by a hash table accessible by the built-in hash
• As well as the following built-ins :
  • cd
  • echo
  • type
  • test
  • exit

All the buit-ins respect the standard POSIX except set, unset and test.

Only the following functions were imported from the C libraries:
_access _chdir _close _closedir _dup _dup2 _environ _execve _exit _fork _free _getcwd _getenv _getpgrp _getpid _getpwnam _getpwuid _getuid _ioctl _isatty _kill _lstat _malloc _memcpy _nanosleep _open _opendir _pipe _read _readdir _setpgid _signal _stat _tcgetattr _tcgetpgrp _tcsetattr _tcsetpgrp _tgetent _tgetstr _tgoto _tputs _uname _unlink _waitpid _write

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