duyetln / tiny-sh

A tiny shell supporting a small subset of shell command syntax

Tiny SH

Overview

A tiny shell command interpreter that supports a subset of shell commands.

Features

• Simple commands: cat, ls, cp, sort, etc...
• IO redirections: <, >, <&, >&, <>, >>, >|.
• Pipes: |.
• Logicals: &&, ||.
• Subshell commands.
• Naive command parallelization: simply join commands to be parallelized with ;;.

Usage

tinysh [OPTION] [FILE]

• Options:
  • -p: print command tree.
  • -t: parallelize commands.
  • -C: turn no clobber option on (for >|).
• File: shell script file to execute.

Syntax of shell command subset

CHAR =  "a"|"b"|"c"|"d"|"e"|"f"|"g"|"h"|"i"|"j"|"k"|"l"|"m"|"n"|"o"|"p"|"q"|"r"|"s"|"t"|"u"|"v"|"w"|"x"|"y"|"z"
       |"A"|"B"|"C"|"D"|"E"|"F"|"G"|"H"|"I"|"J"|"K"|"L"|"M"|"N"|"O"|"P"|"Q"|"R"|"S"|"T"|"U"|"V"|"W"|"X"|"Y"|"Z"
       |"!"|"%"|"+"|","|"-"|"."|"/"|":"|"@"|"^"|"_"
       |DIGIT;

DIGIT = 0|1|2|3|4|5|6|7|8|9;

WORD = CHAR , { CHAR };

IO_NUMBER = DIGIT , { DIGIT };

IO_REDIRECTION = [ IO_NUMBER ] ,  ( "<" , WORD | "<&" , IO_NUMBER | "<>" , WORD | ">" , WORD | ">&" , IO_NUMBER | ">>" , WORD | ">|" , WORD );

SIMPLE_COMMAND = WORD , { WORD };

COMMAND = ( SIMPLE_COMMAND | SUBSHELL_COMMAND ) , { IO_REDIRECTION };

SUBSHELL_COMMAND = "(" , COMMAND_SEQUENCE , ")";

PIPELINES = COMMAND , { "|" , COMMAND };

LOGICALS = PIPELINES , { ( "&&" | "||" ) , PIPELINES };

COMMAND_SEQUENCE = LOGICALS , { ";" , LOGICALS };

COMPUTATION = COMMAND_SEQUENCE , { ";;" , COMMAND_SEQUENCE };

The start symbol is COMPUTATION.