Added initial commit of 'extra' OS assignment.

os/extra/src/Makefile

+CC=gcc
+RM=rm -Rfv
+
+LFLAGS= -lm
+CFLAGS = -std=c99 -pedantic -Wall -Wextra -D_POSIX_SOURCE -D_GNU_SOURCE
+
+ifdef DEBUG
+	CFLAGS += -ggdb -DDEBUG
+else
+	CFLAGS += -g -O2
+endif
+
+all: shell
+
+clean:
+	$(RM) shell *.o input.lex.* input.yacc.*
+
+shell: input.yacc.o input.lex.o shell.o
+	$(CC) $(CFLAGS) $(LFLAGS) -o $@ $^
+
+input.yacc.c: input.y
+	bison --debug --verbose -d -o $@ $<
+
+input.yacc.h: input.yacc.c
+
+input.lex.c: input.l
+	`which flex35 2>/dev/null || which flex 2>/dev/null` \
+		-C --header-file=input.lex.h -o $@ -d $<
+
+input.lex.h: input.lex.c
+
+%.o: %.c
+	$(CC) -c $(CFLAGS) -o $@ $<
+
+input.lex.o:  input.yacc.h input.l.h
+input.yacc.o: input.lex.h

os/extra/src/input.l

+/*
+ * input.l
+ *
+ * Shell input lexer
+ */
+
+%{
+
+// To get rid of the error "‘input’ defined but not used".
+#define YY_NO_INPUT
+
+//#define YY_USER_INIT yyset_debug(0);
+
+#include <stdio.h>
+#include "input.l.h"
+#include "input.yacc.h"
+
+int line_no = 1, column_no = 0;
+
+extern int current_line(void){ return line_no; }
+extern int current_column(void){ return column_no; }
+
+extern void reset_line(void){ line_no = 1; }
+extern void reset_column(void){ column_no = 0; }
+
+%}
+
+%option nounput
+%option noyywrap
+
+%x id
+%x num
+
+id  [a-zA-Z_][[:alnum:]_.]*
+num [0-9]+
+wsp [\r\t ]
+
+%%
+
+    /* Strings, like "abc" */
+\"([^\\"]|\\.)*\" {
+        column_no += yyleng;
+        //yylval.sval = yytext;
+        return STRING;
+    }
+
+    /* Hexadecimal e.g. 0xf00fcafe */
+    /* Octal e.g. 0777 */
+    /* Numbers 0, 42, 9001 etc. */
+0x[0-9a-f]+|{num} {
+        column_no += yyleng;
+        //yylval.sval = yytext;
+        return INTEGER;
+    }
+
+    /* Identifiers */
+{id} {
+        //yylval.sval_annot.str = yytext;
+        //yylval.sval_annot.line = current_line();
+        //yylval.sval_annot.column = current_column();
+        column_no += yyleng;
+        return IDENTIFIER;
+    }
+
+    /* Math operators */
+[-+,()] {
+        column_no++;
+        return *yytext;
+    }
+
+#[^\n]+ { /* ignore comments */ }
+
+\n {
+        line_no++;
+        reset_column();
+        return EOL;
+    }
+
+    /* White space */
+{wsp} { column_no++; }
+
+. {
+        column_no++;
+        fprintf(stderr, "error: illegal character '%c' (0%o)"
+            " at line %d, column %d\n", yytext[0], yytext[0],
+            line_no, column_no);
+        exit(EXIT_FAILURE);
+    }
+
+%%
+

os/extra/src/input.l.h

+extern int current_line(void);
+extern int current_column(void);
+
+extern int yyparse();
+
+extern void reset_line();
+extern void reset_column();

os/extra/src/input.y

+%{
+/*
+ * Shell input grammar (yacc/bison format)
+ */
+
+#include <stdio.h>
+#include <string.h>
+
+// #include "input.func.h"
+#include "input.yacc.h"
+#include "input.lex.h"
+#include "input.l.h"
+
+void yyerror(const char *str)
+{
+    fflush(stdout);
+    fflush(stderr);
+    fprintf(stderr, "error: %s (line %d, column %d)\n", str,
+            current_line(), current_column());
+
+    exit(EXIT_FAILURE);
+}
+
+%}
+
+%token COMMENT IDENTIFIER ARGUMENT STRING INTEGER
+%token EOL
+
+%left '-' '+'
+
+%%
+
+Start: /* empty */
+    | Command EOL
+    ;
+
+Command:
+    | IDENTIFIER
+    | IDENTIFIER Arguments
+    ;
+
+Arguments: ARGUMENT
+    | Arguments ' ' ARGUMENT
+    ;
+
+%%

os/extra/src/shell.c

+/*
+ * Shell implementation using flex/bison.
+ */
+
+#include <stdlib.h>
+#include <stdio.h>
+#include <assert.h>
+
+#include "input.yacc.h"
+#include "input.lex.h"
+#include "input.l.h"
+
+int main(void) {
+    yyset_debug(1);
+
+    if( yyparse() ) {
+        fprintf(stderr, "Error: Parsing failed\n");
+        return EXIT_FAILURE;
+    }
+
+    yylex_destroy();
+
+    if( yyin )
+        fclose(yyin);
+
+    return EXIT_SUCCESS;
+}