xv6-cs450/sh.c

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C
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#include "types.h"
#include "stat.h"
#include "user.h"
#include "fs.h"
#include "fcntl.h"
#define BUFSIZ 512
#define MAXARGS 10
#define MAXNODE 2
#define MAXCMD 2
// an embarrassingly naive shell
// some day a real parse tree; for now ad-hoc
struct ionode {
int token;
char *s;
};
struct ionode iolist[MAXNODE];
int nextio;
struct cmd {
char *argv[MAXARGS];
char argv0buf[BUFSIZ];
int argc;
int token;
};
struct cmd cmdlist[MAXCMD];
int nextcmd;
char buf[BUFSIZ];
int debug = 0;
int parse(char *s);
void runcmd(void);
int ioredirection(void);
int gettoken(char *s, char **token);
int _gettoken(char *s, char **p1, char **p2);
void addio(int token, char *s);
int
main(void)
{
while(1){
puts("$ ");
memset (buf, '\0', sizeof(buf));
gets(buf, sizeof(buf));
if (parse(buf) < 0)
continue;
runcmd();
}
}
int
parse(char *s)
{
char *t;
int c, i;
gettoken(s, 0);
nextio = 0;
nextcmd = 0;
for (i = 0; i < MAXCMD; i++) {
cmdlist[i].argc = 0;
cmdlist[i].token = 0;
}
while (1) {
switch ((c = gettoken(0, &t))) {
case 'w': // Add an argument
if (cmdlist[nextcmd].argc >= MAXARGS) {
printf(2, "too many arguments\n");
return -1;
}
cmdlist[nextcmd].argv[cmdlist[nextcmd].argc++] = t;
break;
case '<': // Input redirection
// Grab the filename from the argument list
if (gettoken(0, &t) != 'w') {
printf(2, "syntax error: < not followed by word\n");
return -1;
}
addio('<', t);
break;
case '>': // Output redirection
// Grab the filename from the argument list
if (gettoken(0, &t) != 'w') {
printf(2, "syntax error: > not followed by word\n");
return -1;
}
addio('>', t);
break;
case ';': // command sequence
case '|': // pipe
cmdlist[nextcmd].token = c;
nextcmd++;
break;
case 0: // String is complete
return 0;
default:
printf(2, "syntax error: bad return %d from gettoken", c);
return -1;
}
}
}
void
runcmd(void)
{
int c, i, r, pid, tfd;
int fdarray[2];
// Return immediately if command line was empty.
if(cmdlist[0].argc == 0) {
if (debug)
printf(2, "EMPTY COMMAND\n");
return;
}
for (c = 0; c <= nextcmd; c++) {
// Clean up command line.
// Read all commands from the filesystem: add an initial '/' to
// the command name.
// This essentially acts like 'PATH=/'.
if (cmdlist[c].argv[0][0] != '/') {
cmdlist[c].argv0buf[0] = '/';
strcpy(cmdlist[c].argv0buf + 1, cmdlist[c].argv[0]);
cmdlist[c].argv[0] = cmdlist[c].argv0buf;
}
cmdlist[c].argv[cmdlist[c].argc] = 0;
// Print the command.
if (debug) {
printf(2, "[%d] SPAWN:", getpid());
for (i = 0; cmdlist[c].argv[i]; i++)
printf(2, " %s", cmdlist[c].argv[i]);
for (i = 0; i < nextio; i++) {
printf(2, "%c %s", iolist[i].token, iolist[i].s);
}
printf(2, "\n");
}
if (strcmp(cmdlist[c].argv[0], "/cd") == 0) {
if (debug) printf (2, "/cd %s is build in\n", cmdlist[c].argv[1]);
chdir(cmdlist[c].argv[1]);
return;
}
if (cmdlist[c].token == '|')
if (pipe(fdarray) < 0)
printf(2, "cmd %d pipe failed\n", c);
pid = fork();
if (pid == 0) {
if (cmdlist[c].token == '|') {
if (close(1) < 0)
printf(2, "close 1 failed\n");
if ((tfd = dup(fdarray[1])) < 0)
printf(2, "dup failed\n");
if (close(fdarray[0]) < 0)
printf(2, "close fdarray[0] failed\n");
if (close(fdarray[1]) < 0)
printf(2, "close fdarray[1] failed\n");
}
if (c > 0 && cmdlist[c-1].token == '|') {
if (close(0) < 0)
printf(2, "close 0 failed\n");
if ((tfd = dup(fdarray[0])) < 0)
printf(2, "dup failed\n");
if (close(fdarray[0]) < 0)
printf(2, "close fdarray[0] failed\n");
if (close(fdarray[1]) < 0)
printf(2, "close fdarray[1] failed\n");
}
if (ioredirection() < 0)
exit();
if ((r = exec(cmdlist[c].argv0buf, (char**) cmdlist[c].argv)) < 0) {
printf(2, "exec %s: %d\n", cmdlist[c].argv[0], r);
exit();
}
} else if (pid > 0) {
int p;
if (debug)
printf(2, "[%d] FORKED child %d\n", getpid(), pid);
if (c > 0 && cmdlist[c-1].token == '|') {
close(fdarray[0]);
close(fdarray[1]);
}
if (cmdlist[c].token != '|') {
if (debug)
printf(2, "[%d] WAIT for children\n", getpid());
do {
p = wait();
if (debug)
printf(2, "[%d] WAIT child %d finished\n", getpid(), p);
} while (p > 0);
if (debug)
printf(2, "[%d] wait finished\n", getpid());
}
}
}
}
int
ioredirection(void)
{
int i, fd;
for (i = 0; i < nextio; i++) {
switch (iolist[i].token) {
case '<':
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if (close(0) < 0)
printf(2, "close 0 failed\n");
if ((fd = open(iolist[i].s, O_RDONLY)) < 0) {
printf(2, "failed to open %s for read: %d", iolist[i].s, fd);
return -1;
}
if (debug)
printf(2, "redirect 0 from %s\n", iolist[i].s);
break;
case '>':
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if (close(1) < 0)
printf(2, "close 1 failed\n");
if ((fd = open(iolist[i].s, O_WRONLY|O_CREATE)) < 0) {
printf(2, "failed to open %s for write: %d", iolist[i].s, fd);
exit();
}
if (debug)
printf(2, "redirect 1 to %s\n", iolist[i].s);
break;
}
}
return 0;
}
void
addio(int token, char *s)
{
if (nextio >= MAXNODE) {
printf(2, "addio: ran out of nodes\n");
return;
}
iolist[nextio].token = token;
iolist[nextio].s = s;
nextio++;
}
// gettoken(s, 0) prepares gettoken for subsequent calls and returns 0.
// gettoken(0, token) parses a shell token from the previously set string,
// null-terminates that token, stores the token pointer in '*token',
// and returns a token ID (0, '<', '>', '|', or 'w').
// Subsequent calls to 'gettoken(0, token)' will return subsequent
// tokens from the string.
int
gettoken(char *s, char **p1)
{
static int c, nc;
static char* np1, *np2;
if (s) {
nc = _gettoken(s, &np1, &np2);
return 0;
}
c = nc;
*p1 = np1;
nc = _gettoken(np2, &np1, &np2);
return c;
}
// Get the next token from string s.
// Set *p1 to the beginning of the token and *p2 just past the token.
// Returns
// 0 for end-of-string;
// < for <;
// > for >;
// | for |;
// w for a word.
//
// Eventually (once we parse the space where the \0 will go),
// words get nul-terminated.
#define WHITESPACE " \t\r\n"
#define SYMBOLS "<|>&;()"
int
_gettoken(char *s, char **p1, char **p2)
{
int t;
if (s == 0) {
if (debug > 1)
printf(2, "GETTOKEN NULL\n");
return 0;
}
if (debug > 1)
printf(2, "GETTOKEN: %s\n", s);
*p1 = 0;
*p2 = 0;
while (strchr(WHITESPACE, *s))
*s++ = 0;
if (*s == 0) {
if (debug > 1)
printf(2, "EOL\n");
return 0;
}
if (strchr(SYMBOLS, *s)) {
t = *s;
*p1 = s;
*s++ = 0;
*p2 = s;
if (debug > 1)
printf(2, "TOK %c\n", t);
return t;
}
*p1 = s;
while (*s && !strchr(WHITESPACE SYMBOLS, *s))
s++;
*p2 = s;
if (debug > 1) {
t = **p2;
**p2 = 0;
printf(2, "WORD: %s\n", *p1);
**p2 = t;
}
return 'w';
}