42shell

42shell is a project in the Codam curriculum requiring you to build a shell with all basic functionality, plus a choice of six extra features.

The seven extra features we have built are:

• Complete management of quoting ✓
• Tab completion for built-ins, command, and files in current directory ✓
• Hash table for executables ✓
• test builtin ✓
• Arithmetic expansion using $(()) ✓
• Command substitution using $() ✓
• Process substitution using <() and >() ✓ (BONUS)

Anything labeled with (BONUS) is not required by the project subject.

Compiling

You can download a pre-compiled binary for Arch, Debian or Ubuntu if you trust our CI build jobs:
[DIRECT DOWNLOAD LINKS]

• Arch Linux
• Debian
• Ubuntu

Compilation has been tested on MacOS Mojave, Debian, Ubuntu, and Arch linux, and requires the following dependencies:

• gcc or clang
• libncurses5-dev
• pkg-config
• meson (0.52 recommended)
• ninja (1.10 recommended)

To compile the shell, run the following commands:

$> meson build
$> cd build
$> ninja

The compiled executable will be called ./cetushell.

Optionally, you can install Criterion and run ninja test to compile and run a limited set of tests.

Usage

To start the shell, run ./cetushell. 42shell will initialize a minimal environment if it receives an empty environment.

This shell currently has the following features:

• Command execution based on PATH
• Hashing of executable names in hashtable, with corresponding hash builtin
• Non-interactive mode through redirection of input OR a file as argument (BONUS)
• Support for comments using #. Aything after a # until the next newline is ignored. (BONUS)
• Internal shell + environment variables, including assignment through assignment words, expansion (using $KEY or ${KEY}) and support for read-only
• Changing the shell prompt by modifying the shell variable PS1
• Pipes (including completion of pipes(BONUS))
• Redirections (>, <, >>, <<, >&, <&)
• Command history using arrow up and arrow down (using $HISTFILE & $HISTSIZE, supports newlines(BONUS))
• Contextual tab completion with support for files, directories, executables, and shell/environment variables.
• Arithmetic expansion using $((expr)), with support for variables and nesting with $((40 + $((2)))) and decimal, hex, and octal numbers.
• Command substitution using $(command), with full support for anything supported in non-interactive mode.
• Process substitution using >(command) to redirect to the process or <(command) to redirect from the command.
• Quotes (", ' and \), including in heredocs and the heredoc end word (i.e. EOF)
• The operators && and || to chain multiple complete commands
• Job control including the required builtins (see below) and job_spec which supports these formats:
  • %-: matches previous job
  • %+: matches current job
  • %n matches job with job id n
  • %string: matches any job that begins with string
  • %?string: matchs any job that contains string
• Command line control:
  • arrow keys to move left and right, ctrl + arrow keys to move per word or line
  • shift + arrow keys left and right to select
  • ctrl+b to copy, ctrl+x to cut, ctrl+v to paste.

Built-in commands:

• cd [-P|-L|'-'] [PATH]: change directory to PATH, or home if PATH is not iven.
  • -P will update $PWD to absolute path if PATH contained symlinks
  • -L will update $PWD to relative path if PATH contained symlinks default)
  • - changes to previous directory (stored in $OLDPWD)
• echo: supports -n(BONUS) to ommit trailing newline
• hash [-r|-i|COMMAND[=PATH]]: manage the command hash table
• jobs [-p|-l] [job_spec ...]: print status of jobs.
  • -p only prints the pgid of the job.
  • -l always print long output with details per process
• fg [job_spec]: but job in foreground. if job_spec is ommited, %+ is assumed.
• bg [job_spec ...]: but all given jobs in foreground. if job_spec is ommited, %+` is assumed.
• set: print all variables (shell and environment)
• unset [KEY ...]: unset all instances of every KEY in shell and environment ariables
• export [-p|KEY[=VALUE] ...]: export every KEY from the shell to the nvironment, or add it th the environment with VALUE if specified.
  • -p will print all environment variables in a valid format to export all of hem.
• setenv: see --help for options and syntax (BONUS)
• unsetenv: see --help for options and syntax (BONUS)
• setshell: see --help for options and syntax (BONUS)
• unsetshell: see --help for options and syntax (BONUS)
• exit [exit_code]: exit the shell. exit code will be exit_code if given, or ost recent status code. ($?)
• type [COMMAND ...]: prints type/location of every COMMAND.
• test with support for [ expr ](BONUS) and !, and the following operators:
  • -a : True if file exists. (BONUS)
  • -b : True if file exists and is a block special file.
  • -c : True if file exists and is a character special file.
  • -d : True if file exists and is a directory.
  • -e : True if file exists.
  • -f : True if file exists and is a regular file.
  • -g : True if file exists and its set-group-id bit is set.
  • -h : True if file exists and is a symbolic link. (BONUS)
  • -L : True if file exists and is a symbolic link.
  • -p : True if file exists and is a named pipe (FIFO).
  • -r : True if file exists and is readable.
  • -S : True if file exists and is a socket.
  • -s : True if file exists and has a size greater than zero.
  • -u : True if file exists and its set-user-id bit is set.
  • -w : True if file exists and is writable.
  • -x : True if file exists and is executable.
  • -z : True if the length of string is zero.
  • -n : True if the length of string is non-zero. (BONUS) str1 OP str2: Arg1 and arg2 are strings, where OP can be:
  • = : True if the strings are equal.
  • == : True if the strings are equal. (BONUS)
  • != : True if the strings are not equal. int1 OP int2: Arg1 and arg2 may be positive or negative integers, where OP can e:
  • -eq : True if arg1 is equal to arg2.
  • -ne : True if arg1 is not equal to arg2.
  • -gt : True if arg1 is greater than arg2. (BONUS)
  • -ge : True if arg1 is greater than or equal to arg2.
  • -lt : True if arg1 is less than arg2.
  • -le : True if arg1 is less than or equal to arg2.