shellsim

A self-contained simulation of a bash-like shell, with scripting, piping, streaming functionality and internal filesystem.

Commands

Basic commands

• Change current working directory: cd DIR_PATH
• List items in directory: ls / ls DIR_PATH
• Make directory: mkdir DIR_NAME
• Remove directory: rmdir DIR_NAME
• Print current working directory: pwd
• Create new file: touch FILE_PATH
• Delete file: rm FILE_PATH
• Manage users: user add/del/mod USERNAME OPTIONS
• Execute command as superuser: sudo COMMAND

File handling

• Echo input to output: echo INPUT
• Concatenate file contents: cat FILE_NAME1 FILE_NAME2 etc.

Variables and scripting

• Declare string variable: declare VAR_NAME=VALUE
• Declare variable as result of expression: declare VAR_NAME=EXPR
• Read in input stdin or user to variable: read VAR_NAME
• Conditional execution: if [ COND ] ? TRUE_STATEMENT : FALSE_STATEMENT
• Run shell script: run FILE_PATH

Package management

• Manage external packages: pkgman get / remove PKG_1 PKG_2 etc.

Pkgman works by checking the module_directory object in modules.py. Functions there with a corresponding name will be added as attributes of the Computer object callable as commands in the shell. pkgman remove will delete the attribute, thus unlinking the function.

Advanced Features

Piping

COMMAND 1 | COMMAND 2 will supply the output of command 1 as arguments for command 2. Newlines are treated as argument separators. In the case of scripts, arguments are stored in an input stream which can be read from using the read command.

Streaming

COMMAND 1 > FILE_NAME.txt will stream the output of command 1 to file_name.txt. > overwrites existing file content, >> appends to existing file content.

Script flow

• goto LABEL will goto the line with the label :LABEL, pushing the current position onto the return stack. Useable in shell scripts only.
• return will return to the position in the script after your last goto statement. Useable in shell scripts only.

Filename matching

rm and cat support filename matching. * to match anything, ? to match a single character, [abc] to match any character in abc, [^abc] to match any character not in abc.

Lined (LINe EDitor)

Based on the ed editor. Commands should be issued in the format A,BcP where A,B is a line range (defaults to the last line you added), c is the command and P the arguments. If you use , in place of A,B the range is the entire document. If you just use a single line number it will only target that single line. cat file.txt | lined will push all commands in file.txt to lined.

Supports the following commands:

• a: Append after line, switch to insert mode (Treat all commands as lines to be inserted until lined receives a single .)
• i: Insert before line, switch to insert mode
• c: Change
• d: Delete
• l: List
• w filename: Write to filename, outputing number of characters written on successful write
• !command: Run command in shell and add output to document
• s/re/new: Substitute everything in range based on regular expression re with the text new
• g/re/p: Global search for all lines that match regex re, issuing command string p. Command strings can be separated by \ for multiple commands (Commands that insert lines or delete them will mess up under the current implementation)
• q: Quit