xv6/sh.c

// Shell.

#include "types.h"
#include "user.h"
#include "fcntl.h"

// Parsed command representation
#define EXEC 1
#define REDIR 2
#define PIPE 3
#define LIST 4
#define BACK 5

#define MAXARGS 10

struct cmd {
    int type;
};

struct execcmd {
    int type;
    char *argv[MAXARGS];
    char *eargv[MAXARGS];
};

struct redircmd {
    int type;
    struct cmd *cmd;
    char *file;
    char *efile;
    int mode;
    int fd;
};

struct pipecmd {
    int type;
    struct cmd *left;
    struct cmd *right;
};

struct listcmd {
    int type;
    struct cmd *left;
    struct cmd *right;
};

struct backcmd {
    int type;
    struct cmd *cmd;
};
int fork1(void); // Fork but panics on failure.
void panic(char*);
struct cmd *parsecmd(char*);

// Execute cmd. Never returns.
void
runcmd(struct cmd *cmd)
{
    int p[2];
    struct backcmd *bcmd;
    struct execcmd *ecmd;
    struct listcmd *lcmd;
    struct pipecmd *pcmd;
    struct redircmd *rcmd;

    if(cmd == 0)
        exit();

    switch(cmd->type){
        default:
            panic("runcmd");

        case EXEC:
            ecmd = (struct execcmd*)cmd;
            if(ecmd->argv[0] == 0)
                exit();
            exec(ecmd->argv[0], ecmd->argv);
            printf(2, "exec %s failed
", ecmd->argv[0]);
            break;

        case REDIR:
            rcmd = (struct redircmd*)cmd;
            close(rcmd->fd);
            if(open(rcmd->file, rcmd->mode) < 0){
                printf(2, "open %s failed
", rcmd->file);
                exit();
            }
            runcmd(rcmd->cmd);
            break;

        case LIST:
            lcmd = (struct listcmd*)cmd;
            if(fork1() == 0)
                runcmd(lcmd->left);
            wait();
            runcmd(lcmd->right);
            break;



        case PIPE:
            pcmd = (struct pipecmd*)cmd;
            if(pipe(p) < 0)
                panic("pipe");
            if(fork1() == 0){
                close(1);
                dup(p[1]);
                close(p[0]);
                close(p[1]);
                runcmd(pcmd->left);
            }
            if(fork1() == 0){
                close(0);
                dup(p[0]);
                close(p[0]);
                close(p[1]);
                runcmd(pcmd->right);
            }
            close(p[0]);
            close(p[1]);
            wait();
            wait();
            break;

        case BACK:
            bcmd = (struct backcmd*)cmd;
            if(fork1() == 0)
                runcmd(bcmd->cmd);
            break;
    }
    exit();
}

int
getcmd(char *buf, int nbuf)
{
    printf(2, "$ ");
    memset(buf, 0, nbuf);
    gets(buf, nbuf);
    if(buf[0] == 0) // EOF
        return -1;
    return 0;
}

int
main(void)
{
    static char buf[100];
    int fd;

    // Assumes three file descriptors open.
    while((fd = open("console", O_RDWR)) >= 0){
        if(fd >= 3){
            close(fd);
            break;
        }
    }

    // Read and run input commands.
    while(getcmd(buf, sizeof(buf)) >= 0){
        if(buf[0] == ’c’ && buf[1] == ’d’ && buf[2] == ’ ’){
            // Clumsy but will have to do for now.
            // Chdir has no effect on the parent if run in the child.
            buf[strlen(buf)-1] = 0; // chop 

            if(chdir(buf+3) < 0)
                printf(2, "cannot cd %s
", buf+3);
            continue;
        }
        if(fork1() == 0)
            runcmd(parsecmd(buf));
        wait();
    }
    exit();
}

void
panic(char *s)
{
    printf(2, "%s
", s);
    exit();
}

int
fork1(void)
{
    int pid;

    pid = fork();
    if(pid == -1)
        panic("fork");
    return pid;
}

// Constructors

struct cmd*
execcmd(void)
{
    struct execcmd *cmd;

    cmd = malloc(sizeof(*cmd));
    memset(cmd, 0, sizeof(*cmd));
    cmd->type = EXEC;
    return (struct cmd*)cmd;
}

struct cmd*
redircmd(struct cmd *subcmd, char *file, char *efile, int mode, int fd)
{
    struct redircmd *cmd;

    cmd = malloc(sizeof(*cmd));
    memset(cmd, 0, sizeof(*cmd));
    cmd->type = REDIR;
    cmd->cmd = subcmd;
    cmd->file = file;
    cmd->efile = efile;
    cmd->mode = mode;
    cmd->fd = fd;
    return (struct cmd*)cmd;
}

struct cmd*
pipecmd(struct cmd *left, struct cmd *right)
{
    struct pipecmd *cmd;

    cmd = malloc(sizeof(*cmd));
    memset(cmd, 0, sizeof(*cmd));
    cmd->type = PIPE;
    cmd->left = left;
    cmd->right = right;
    return (struct cmd*)cmd;
}

struct cmd*
listcmd(struct cmd *left, struct cmd *right)
{
    struct listcmd *cmd;

    cmd = malloc(sizeof(*cmd));
    memset(cmd, 0, sizeof(*cmd));
    cmd->type = LIST;
    cmd->left = left;
    cmd->right = right;
    return (struct cmd*)cmd;
}

struct cmd*
backcmd(struct cmd *subcmd)
{
    struct backcmd *cmd;

    cmd = malloc(sizeof(*cmd));
    memset(cmd, 0, sizeof(*cmd));
    cmd->type = BACK;
    cmd->cmd = subcmd;
    return (struct cmd*)cmd;
}

// Parsing

char whitespace[] = " 	
v";
char symbols[] = "<|>&;()";

int
gettoken(char **ps, char *es, char **q, char **eq)
{
    char *s;
    int ret;

    s = *ps;
    while(s < es && strchr(whitespace, *s))
        s++;
    if(q)
        *q = s;
    ret = *s;
    switch(*s){
        case 0:
            break;
        case ’|’:
        case ’(’:
            case ’)’:
            case ’;’:
            case ’&’:
            case ’<’:
            s++;
            break;
            case ’>’:
            s++;
            if(*s == ’>’){
                ret = ’+’;
                s++;
            }
            break;
            default:
            ret = ’a’;
            while(s < es && !strchr(whitespace, *s) && !strchr(symbols, *s))
                s++;
            break;
    }
    if(eq)
        *eq = s;

    while(s < es && strchr(whitespace, *s))
        s++;
    *ps = s;
    return ret;
}

int
peek(char **ps, char *es, char *toks)
{
    char *s;

    s = *ps;
    while(s < es && strchr(whitespace, *s))
        s++;
    *ps = s;
    return *s && strchr(toks, *s);
}

struct cmd *parseline(char**, char*);
struct cmd *parsepipe(char**, char*);
struct cmd *parseexec(char**, char*);
struct cmd *nulterminate(struct cmd*);

struct cmd*
parsecmd(char *s)
{
    char *es;
    struct cmd *cmd;

    es = s + strlen(s);
    cmd = parseline(&s, es);
    peek(&s, es, "");
    if(s != es){
        printf(2, "leftovers: %s
", s);
        panic("syntax");
    }
    nulterminate(cmd);
    return cmd;
}

struct cmd*
parseline(char **ps, char *es)
{
    struct cmd *cmd;

    cmd = parsepipe(ps, es);
    while(peek(ps, es, "&")){
        gettoken(ps, es, 0, 0);
        cmd = backcmd(cmd);
    }
    if(peek(ps, es, ";")){
        gettoken(ps, es, 0, 0);
        cmd = listcmd(cmd, parseline(ps, es));
    }
    return cmd;
}

struct cmd*
parsepipe(char **ps, char *es)
{
    struct cmd *cmd;

    cmd = parseexec(ps, es);
    if(peek(ps, es, "|")){
        gettoken(ps, es, 0, 0);
        cmd = pipecmd(cmd, parsepipe(ps, es));
    }
    return cmd;
}

struct cmd*
parseredirs(struct cmd *cmd, char **ps, char *es)
{
    int tok;
    char *q, *eq;

    while(peek(ps, es, "<>")){
        tok = gettoken(ps, es, 0, 0);
        if(gettoken(ps, es, &q, &eq) != ’a’)
            panic("missing file for redirection");
        switch(tok){
            case ’<’:
                cmd = redircmd(cmd, q, eq, O_RDONLY, 0);
                break;
            case ’>’:
                cmd = redircmd(cmd, q, eq, O_WRONLY|O_CREATE, 1);
                break;
            case ’+’: // >>
                cmd = redircmd(cmd, q, eq, O_WRONLY|O_CREATE, 1);
                break;
        }
    }
    return cmd;
}

struct cmd*
parseblock(char **ps, char *es)
{
    struct cmd *cmd;

    if(!peek(ps, es, "("))
        panic("parseblock");
    gettoken(ps, es, 0, 0);
    cmd = parseline(ps, es);
    if(!peek(ps, es, ")"))
        panic("syntax - missing )");
    gettoken(ps, es, 0, 0);
    cmd = parseredirs(cmd, ps, es);
    return cmd;
}

struct cmd*
parseexec(char **ps, char *es)
{
    char *q, *eq;
    int tok, argc;
    struct execcmd *cmd;
    struct cmd *ret;

    if(peek(ps, es, "("))
        return parseblock(ps, es);

    ret = execcmd();
    cmd = (struct execcmd*)ret;

    argc = 0;
    ret = parseredirs(ret, ps, es);
    while(!peek(ps, es, "|)&;")){
        if((tok=gettoken(ps, es, &q, &eq)) == 0)
            break;
        if(tok != ’a’)
            panic("syntax");
        cmd->argv[argc] = q;
        cmd->eargv[argc] = eq;
        argc++;
        if(argc >= MAXARGS)
            panic("too many args");
        ret = parseredirs(ret, ps, es);
    }
    cmd->argv[argc] = 0;
    cmd->eargv[argc] = 0;
    return ret;
}

// NUL-terminate all the counted strings.
struct cmd*
nulterminate(struct cmd *cmd)
{
    int i;
    struct backcmd *bcmd;
    struct execcmd *ecmd;
    struct listcmd *lcmd;
    struct pipecmd *pcmd;
    struct redircmd *rcmd;

    if(cmd == 0)
        return 0;

    switch(cmd->type){
        case EXEC:
            ecmd = (struct execcmd*)cmd;
            for(i=0; ecmd->argv[i]; i++)
                *ecmd->eargv[i] = 0;
            break;

        case REDIR:
            rcmd = (struct redircmd*)cmd;
            nulterminate(rcmd->cmd);
            *rcmd->efile = 0;
            break;

        case PIPE:
            pcmd = (struct pipecmd*)cmd;
            nulterminate(pcmd->left);
            nulterminate(pcmd->right);
            break;

        case LIST:
            lcmd = (struct listcmd*)cmd;
            nulterminate(lcmd->left);
            nulterminate(lcmd->right);
            break;

        case BACK:
            bcmd = (struct backcmd*)cmd;
            nulterminate(bcmd->cmd);
            break;
    }
    return cmd;
}