/*-
 * SPDX-License-Identifier: BSD-3-Clause
 *
 * Copyright (c) 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Kenneth Almquist.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <paths.h>
#include <signal.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/resource.h>
#include <errno.h>

/*
 * Evaluate a command.
 */

#include "shell.h"
#include "nodes.h"
#include "syntax.h"
#include "expand.h"
#include "parser.h"
#include "jobs.h"
#include "eval.h"
#include "builtins.h"
#include "options.h"
#include "exec.h"
#include "redir.h"
#include "input.h"
#include "output.h"
#include "trap.h"
#include "var.h"
#include "memalloc.h"
#include "error.h"
#include "show.h"
#include "mystring.h"
#ifndef NO_HISTORY
#include "myhistedit.h"
#endif


int evalskip;                   /* set if we are skipping commands */
int skipcount;                  /* number of levels to skip */
static int loopnest;            /* current loop nesting level */
int funcnest;                   /* depth of function calls */
static int builtin_flags;       /* evalcommand flags for builtins */


char *commandname;
struct arglist *cmdenviron;
int exitstatus;                 /* exit status of last command */
int oexitstatus;                /* saved exit status */


static void evalloop(union node *, int);
static void evalfor(union node *, int);
static union node *evalcase(union node *);
static void evalsubshell(union node *, int);
static void evalredir(union node *, int);
static void exphere(union node *, struct arglist *);
static void expredir(union node *);
static void evalpipe(union node *);
static int is_valid_fast_cmdsubst(union node *n);
static void evalcommand(union node *, int, struct backcmd *);
static void prehash(union node *);


/*
 * Called to reset things after an exception.
 */

void
reseteval(void)
{
        evalskip = 0;
        loopnest = 0;
}


/*
 * The eval command.
 */

int
evalcmd(int argc, char **argv)
{
        char *p;
        char *concat;
        char **ap;

        if (argc > 1) {
                p = argv[1];
                if (argc > 2) {
                        STARTSTACKSTR(concat);
                        ap = argv + 2;
                        for (;;) {
                                STPUTS(p, concat);
                                if ((p = *ap++) == NULL)
                                        break;
                                STPUTC(' ', concat);
                        }
                        STPUTC('\0', concat);
                        p = grabstackstr(concat);
                }
                evalstring(p, builtin_flags);
        } else
                exitstatus = 0;
        return exitstatus;
}


/*
 * Execute a command or commands contained in a string.
 */

void
evalstring(const char *s, int flags)
{
        union node *n;
        struct stackmark smark;
        int flags_exit;
        int any;

        flags_exit = flags & EV_EXIT;
        flags &= ~EV_EXIT;
        any = 0;
        setstackmark(&smark);
        setinputstring(s, 1);
        while ((n = parsecmd(0)) != NEOF) {
                if (n != NULL && !nflag) {
                        if (flags_exit && preadateof())
                                evaltree(n, flags | EV_EXIT);
                        else
                                evaltree(n, flags);
                        any = 1;
                        if (evalskip)
                                break;
                }
                popstackmark(&smark);
                setstackmark(&smark);
        }
        popfile();
        popstackmark(&smark);
        if (!any)
                exitstatus = 0;
        if (flags_exit)
                exraise(EXEXIT);
}


/*
 * Evaluate a parse tree.  The value is left in the global variable
 * exitstatus.
 */

void
evaltree(union node *n, int flags)
{
        int do_etest;
        union node *next;
        struct stackmark smark;

        setstackmark(&smark);
        do_etest = 0;
        if (n == NULL) {
                TRACE(("evaltree(NULL) called\n"));
                exitstatus = 0;
                goto out;
        }
        do {
                next = NULL;
#ifndef NO_HISTORY
                displayhist = 1;        /* show history substitutions done with fc */
#endif
                TRACE(("evaltree(%p: %d) called\n", (void *)n, n->type));
                switch (n->type) {
                case NSEMI:
                        evaltree(n->nbinary.ch1, flags & ~EV_EXIT);
                        if (evalskip)
                                goto out;
                        next = n->nbinary.ch2;
                        break;
                case NAND:
                        evaltree(n->nbinary.ch1, EV_TESTED);
                        if (evalskip || exitstatus != 0) {
                                goto out;
                        }
                        next = n->nbinary.ch2;
                        break;
                case NOR:
                        evaltree(n->nbinary.ch1, EV_TESTED);
                        if (evalskip || exitstatus == 0)
                                goto out;
                        next = n->nbinary.ch2;
                        break;
                case NREDIR:
                        evalredir(n, flags);
                        break;
                case NSUBSHELL:
                        evalsubshell(n, flags);
                        do_etest = !(flags & EV_TESTED);
                        break;
                case NBACKGND:
                        evalsubshell(n, flags);
                        break;
                case NIF: {
                        evaltree(n->nif.test, EV_TESTED);
                        if (evalskip)
                                goto out;
                        if (exitstatus == 0)
                                next = n->nif.ifpart;
                        else if (n->nif.elsepart)
                                next = n->nif.elsepart;
                        else
                                exitstatus = 0;
                        break;
                }
                case NWHILE:
                case NUNTIL:
                        evalloop(n, flags & ~EV_EXIT);
                        break;
                case NFOR:
                        evalfor(n, flags & ~EV_EXIT);
                        break;
                case NCASE:
                        next = evalcase(n);
                        break;
                case NCLIST:
                        next = n->nclist.body;
                        break;
                case NCLISTFALLTHRU:
                        if (n->nclist.body) {
                                evaltree(n->nclist.body, flags & ~EV_EXIT);
                                if (evalskip)
                                        goto out;
                        }
                        next = n->nclist.next;
                        break;
                case NDEFUN:
                        defun(n->narg.text, n->narg.next);
                        exitstatus = 0;
                        break;
                case NNOT:
                        evaltree(n->nnot.com, EV_TESTED);
                        if (evalskip)
                                goto out;
                        exitstatus = !exitstatus;
                        break;

                case NPIPE:
                        evalpipe(n);
                        do_etest = !(flags & EV_TESTED);
                        break;
                case NCMD:
                        evalcommand(n, flags, (struct backcmd *)NULL);
                        do_etest = !(flags & EV_TESTED);
                        break;
                default:
                        out1fmt("Node type = %d\n", n->type);
                        flushout(&output);
                        break;
                }
                n = next;
                popstackmark(&smark);
                setstackmark(&smark);
        } while (n != NULL);
out:
        popstackmark(&smark);
        if (pendingsig)
                dotrap();
        if (eflag && exitstatus != 0 && do_etest)
                exitshell(exitstatus);
        if (flags & EV_EXIT)
                exraise(EXEXIT);
}


static void
evalloop(union node *n, int flags)
{
        int status;

        loopnest++;
        status = 0;
        for (;;) {
                if (!evalskip)
                        evaltree(n->nbinary.ch1, EV_TESTED);
                if (evalskip) {
                        if (evalskip == SKIPCONT && --skipcount <= 0) {
                                evalskip = 0;
                                continue;
                        }
                        if (evalskip == SKIPBREAK && --skipcount <= 0)
                                evalskip = 0;
                        if (evalskip == SKIPRETURN)
                                status = exitstatus;
                        break;
                }
                if (n->type == NWHILE) {
                        if (exitstatus != 0)
                                break;
                } else {
                        if (exitstatus == 0)
                                break;
                }
                evaltree(n->nbinary.ch2, flags);
                status = exitstatus;
        }
        loopnest--;
        exitstatus = status;
}



static void
evalfor(union node *n, int flags)
{
        struct arglist arglist;
        union node *argp;
        int i;
        int status;

        emptyarglist(&arglist);
        for (argp = n->nfor.args ; argp ; argp = argp->narg.next) {
                oexitstatus = exitstatus;
                expandarg(argp, &arglist, EXP_FULL | EXP_TILDE);
        }

        loopnest++;
        status = 0;
        for (i = 0; i < arglist.count; i++) {
                setvar(n->nfor.var, arglist.args[i], 0);
                evaltree(n->nfor.body, flags);
                status = exitstatus;
                if (evalskip) {
                        if (evalskip == SKIPCONT && --skipcount <= 0) {
                                evalskip = 0;
                                continue;
                        }
                        if (evalskip == SKIPBREAK && --skipcount <= 0)
                                evalskip = 0;
                        break;
                }
        }
        loopnest--;
        exitstatus = status;
}


/*
 * Evaluate a case statement, returning the selected tree.
 *
 * The exit status needs care to get right.
 */

static union node *
evalcase(union node *n)
{
        union node *cp;
        union node *patp;
        struct arglist arglist;

        emptyarglist(&arglist);
        oexitstatus = exitstatus;
        expandarg(n->ncase.expr, &arglist, EXP_TILDE);
        for (cp = n->ncase.cases ; cp ; cp = cp->nclist.next) {
                for (patp = cp->nclist.pattern ; patp ; patp = patp->narg.next) {
                        if (casematch(patp, arglist.args[0])) {
                                while (cp->nclist.next &&
                                    cp->type == NCLISTFALLTHRU &&
                                    cp->nclist.body == NULL)
                                        cp = cp->nclist.next;
                                if (cp->nclist.next &&
                                    cp->type == NCLISTFALLTHRU)
                                        return (cp);
                                if (cp->nclist.body == NULL)
                                        exitstatus = 0;
                                return (cp->nclist.body);
                        }
                }
        }
        exitstatus = 0;
        return (NULL);
}



/*
 * Kick off a subshell to evaluate a tree.
 */

static void
evalsubshell(union node *n, int flags)
{
        struct job *jp;
        int backgnd = (n->type == NBACKGND);

        oexitstatus = exitstatus;
        expredir(n->nredir.redirect);
        if ((!backgnd && flags & EV_EXIT && !have_traps()) ||
                        forkshell(jp = makejob(n, 1), n, backgnd) == 0) {
                if (backgnd)
                        flags &=~ EV_TESTED;
                redirect(n->nredir.redirect, 0);
                evaltree(n->nredir.n, flags | EV_EXIT); /* never returns */
        } else if (! backgnd) {
                INTOFF;
                exitstatus = waitforjob(jp, (int *)NULL);
                INTON;
        } else
                exitstatus = 0;
}


/*
 * Evaluate a redirected compound command.
 */

static void
evalredir(union node *n, int flags)
{
        struct jmploc jmploc;
        struct jmploc *savehandler;
        volatile int in_redirect = 1;

        oexitstatus = exitstatus;
        expredir(n->nredir.redirect);
        savehandler = handler;
        if (setjmp(jmploc.loc)) {
                int e;

                handler = savehandler;
                e = exception;
                popredir();
                if (e == EXERROR && in_redirect) {
                        FORCEINTON;
                        return;
                }
                longjmp(handler->loc, 1);
        } else {
                INTOFF;
                handler = &jmploc;
                redirect(n->nredir.redirect, REDIR_PUSH);
                in_redirect = 0;
                INTON;
                evaltree(n->nredir.n, flags);
        }
        INTOFF;
        handler = savehandler;
        popredir();
        INTON;
}


static void
exphere(union node *redir, struct arglist *fn)
{
        struct jmploc jmploc;
        struct jmploc *savehandler;
        struct localvar *savelocalvars;
        int need_longjmp = 0;
        unsigned char saveoptreset;

        redir->nhere.expdoc = "";
        savelocalvars = localvars;
        localvars = NULL;
        saveoptreset = shellparam.reset;
        forcelocal++;
        savehandler = handler;
        if (setjmp(jmploc.loc))
                need_longjmp = exception != EXERROR;
        else {
                handler = &jmploc;
                expandarg(redir->nhere.doc, fn, 0);
                redir->nhere.expdoc = fn->args[0];
                INTOFF;
        }
        handler = savehandler;
        forcelocal--;
        poplocalvars();
        localvars = savelocalvars;
        shellparam.reset = saveoptreset;
        if (need_longjmp)
                longjmp(handler->loc, 1);
        INTON;
}


/*
 * Compute the names of the files in a redirection list.
 */

static void
expredir(union node *n)
{
        union node *redir;

        for (redir = n ; redir ; redir = redir->nfile.next) {
                struct arglist fn;
                emptyarglist(&fn);
                switch (redir->type) {
                case NFROM:
                case NTO:
                case NFROMTO:
                case NAPPEND:
                case NCLOBBER:
                        expandarg(redir->nfile.fname, &fn, EXP_TILDE);
                        redir->nfile.expfname = fn.args[0];
                        break;
                case NFROMFD:
                case NTOFD:
                        if (redir->ndup.vname) {
                                expandarg(redir->ndup.vname, &fn, EXP_TILDE);
                                fixredir(redir, fn.args[0], 1);
                        }
                        break;
                case NXHERE:
                        exphere(redir, &fn);
                        break;
                }
        }
}



/*
 * Evaluate a pipeline.  All the processes in the pipeline are children
 * of the process creating the pipeline.  (This differs from some versions
 * of the shell, which make the last process in a pipeline the parent
 * of all the rest.)
 */

static void
evalpipe(union node *n)
{
        struct job *jp;
        struct nodelist *lp;
        int pipelen;
        int prevfd;
        int pip[2];

        TRACE(("evalpipe(%p) called\n", (void *)n));
        pipelen = 0;
        for (lp = n->npipe.cmdlist ; lp ; lp = lp->next)
                pipelen++;
        INTOFF;
        jp = makejob(n, pipelen);
        prevfd = -1;
        for (lp = n->npipe.cmdlist ; lp ; lp = lp->next) {
                prehash(lp->n);
                pip[1] = -1;
                if (lp->next) {
                        if (pipe(pip) < 0) {
                                if (prevfd >= 0)
                                        close(prevfd);
                                error("Pipe call failed: %s", strerror(errno));
                        }
                }
                if (forkshell(jp, lp->n, n->npipe.backgnd) == 0) {
                        INTON;
                        if (prevfd > 0) {
                                dup2(prevfd, 0);
                                close(prevfd);
                        }
                        if (pip[1] >= 0) {
                                if (!(prevfd >= 0 && pip[0] == 0))
                                        close(pip[0]);
                                if (pip[1] != 1) {
                                        dup2(pip[1], 1);
                                        close(pip[1]);
                                }
                        }
                        evaltree(lp->n, EV_EXIT);
                }
                if (prevfd >= 0)
                        close(prevfd);
                prevfd = pip[0];
                if (pip[1] != -1)
                        close(pip[1]);
        }
        INTON;
        if (n->npipe.backgnd == 0) {
                INTOFF;
                exitstatus = waitforjob(jp, (int *)NULL);
                TRACE(("evalpipe:  job done exit status %d\n", exitstatus));
                INTON;
        } else
                exitstatus = 0;
}



static int
is_valid_fast_cmdsubst(union node *n)
{

        return (n->type == NCMD);
}

/*
 * Execute a command inside back quotes.  If it's a builtin command, we
 * want to save its output in a block obtained from malloc.  Otherwise
 * we fork off a subprocess and get the output of the command via a pipe.
 * Should be called with interrupts off.
 */

void
evalbackcmd(union node *n, struct backcmd *result)
{
        int pip[2];
        struct job *jp;
        struct stackmark smark;
        struct jmploc jmploc;
        struct jmploc *savehandler;
        struct localvar *savelocalvars;
        unsigned char saveoptreset;

        result->fd = -1;
        result->buf = NULL;
        result->nleft = 0;
        result->jp = NULL;
        if (n == NULL) {
                exitstatus = 0;
                return;
        }
        setstackmark(&smark);
        exitstatus = oexitstatus;
        if (is_valid_fast_cmdsubst(n)) {
                savelocalvars = localvars;
                localvars = NULL;
                saveoptreset = shellparam.reset;
                forcelocal++;
                savehandler = handler;
                if (setjmp(jmploc.loc)) {
                        if (exception == EXERROR)
                                /* nothing */;
                        else if (exception != 0) {
                                handler = savehandler;
                                forcelocal--;
                                poplocalvars();
                                localvars = savelocalvars;
                                shellparam.reset = saveoptreset;
                                longjmp(handler->loc, 1);
                        }
                } else {
                        handler = &jmploc;
                        evalcommand(n, EV_BACKCMD, result);
                }
                handler = savehandler;
                forcelocal--;
                poplocalvars();
                localvars = savelocalvars;
                shellparam.reset = saveoptreset;
        } else {
                if (pipe(pip) < 0)
                        error("Pipe call failed: %s", strerror(errno));
                jp = makejob(n, 1);
                if (forkshell(jp, n, FORK_NOJOB) == 0) {
                        FORCEINTON;
                        close(pip[0]);
                        if (pip[1] != 1) {
                                dup2(pip[1], 1);
                                close(pip[1]);
                        }
                        evaltree(n, EV_EXIT);
                }
                close(pip[1]);
                result->fd = pip[0];
                result->jp = jp;
        }
        popstackmark(&smark);
        TRACE(("evalbackcmd done: fd=%d buf=%p nleft=%d jp=%p\n",
                result->fd, result->buf, result->nleft, result->jp));
}

static int
mustexpandto(const char *argtext, const char *mask)
{
        for (;;) {
                if (*argtext == CTLQUOTEMARK || *argtext == CTLQUOTEEND) {
                        argtext++;
                        continue;
                }
                if (*argtext == CTLESC)
                        argtext++;
                else if (BASESYNTAX[(int)*argtext] == CCTL)
                        return (0);
                if (*argtext != *mask)
                        return (0);
                if (*argtext == '\0')
                        return (1);
                argtext++;
                mask++;
        }
}

static int
isdeclarationcmd(struct narg *arg)
{
        int have_command = 0;

        if (arg == NULL)
                return (0);
        while (mustexpandto(arg->text, "command")) {
                have_command = 1;
                arg = &arg->next->narg;
                if (arg == NULL)
                        return (0);
                /*
                 * To also allow "command -p" and "command --" as part of
                 * a declaration command, add code here.
                 * We do not do this, as ksh does not do it either and it
                 * is not required by POSIX.
                 */
        }
        return (mustexpandto(arg->text, "export") ||
            mustexpandto(arg->text, "readonly") ||
            (mustexpandto(arg->text, "local") &&
                (have_command || !isfunc("local"))));
}

static void
xtracecommand(struct arglist *varlist, int argc, char **argv)
{
        char sep = 0;
        const char *text, *p, *ps4;
        int i;

        ps4 = expandstr(ps4val());
        out2str(ps4 != NULL ? ps4 : ps4val());
        for (i = 0; i < varlist->count; i++) {
                text = varlist->args[i];
                if (sep != 0)
                        out2c(' ');
                p = strchr(text, '=');
                if (p != NULL) {
                        p++;
                        outbin(text, p - text, out2);
                        out2qstr(p);
                } else
                        out2qstr(text);
                sep = ' ';
        }
        for (i = 0; i < argc; i++) {
                text = argv[i];
                if (sep != 0)
                        out2c(' ');
                out2qstr(text);
                sep = ' ';
        }
        out2c('\n');
        flushout(&errout);
}

/*
 * Check if a builtin can safely be executed in the same process,
 * even though it should be in a subshell (command substitution).
 * Note that jobid, jobs, times and trap can show information not
 * available in a child process; this is deliberate.
 * The arguments should already have been expanded.
 */
static int
safe_builtin(int idx, int argc, char **argv)
{
        /* Generated from builtins.def. */
        if (safe_builtin_always(idx))
                return (1);
        if (idx == EXPORTCMD || idx == TRAPCMD || idx == ULIMITCMD ||
            idx == UMASKCMD)
                return (argc <= 1 || (argc == 2 && argv[1][0] == '-'));
        if (idx == SETCMD)
                return (argc <= 1 || (argc == 2 && (argv[1][0] == '-' ||
                    argv[1][0] == '+') && argv[1][1] == 'o' &&
                    argv[1][2] == '\0'));
        return (0);
}

/*
 * Execute a simple command.
 * Note: This may or may not return if (flags & EV_EXIT).
 */

static void
evalcommand(union node *cmd, int flags, struct backcmd *backcmd)
{
        union node *argp;
        struct arglist arglist;
        struct arglist varlist;
        char **argv;
        int argc;
        char **envp;
        int varflag;
        int mode;
        int pip[2];
        struct cmdentry cmdentry;
        struct job *jp;
        struct jmploc jmploc;
        struct jmploc *savehandler;
        char *savecmdname;
        struct shparam saveparam;
        struct localvar *savelocalvars;
        struct parsefile *savetopfile;
        volatile int e;
        char *lastarg;
        int signaled;
        int do_clearcmdentry;
        const char *path = pathval();
        int i;

        /* First expand the arguments. */
        TRACE(("evalcommand(%p, %d) called\n", (void *)cmd, flags));
        emptyarglist(&arglist);
        emptyarglist(&varlist);
        varflag = 1;
        jp = NULL;
        do_clearcmdentry = 0;
        oexitstatus = exitstatus;
        exitstatus = 0;
        /* Add one slot at the beginning for tryexec(). */
        appendarglist(&arglist, nullstr);
        for (argp = cmd->ncmd.args ; argp ; argp = argp->narg.next) {
                if (varflag && isassignment(argp->narg.text)) {
                        expandarg(argp, varflag == 1 ? &varlist : &arglist,
                            EXP_VARTILDE);
                        continue;
                } else if (varflag == 1)
                        varflag = isdeclarationcmd(&argp->narg) ? 2 : 0;
                expandarg(argp, &arglist, EXP_FULL | EXP_TILDE);
        }
        appendarglist(&arglist, nullstr);
        expredir(cmd->ncmd.redirect);
        argc = arglist.count - 2;
        argv = &arglist.args[1];

        argv[argc] = NULL;
        lastarg = NULL;
        if (iflag && funcnest == 0 && argc > 0)
                lastarg = argv[argc - 1];

        /* Print the command if xflag is set. */
        if (xflag)
                xtracecommand(&varlist, argc, argv);

        /* Now locate the command. */
        if (argc == 0) {
                /* Variable assignment(s) without command */
                cmdentry.cmdtype = CMDBUILTIN;
                cmdentry.u.index = BLTINCMD;
                cmdentry.special = 0;
        } else {
                static const char PATH[] = "PATH=";
                int cmd_flags = 0, bltinonly = 0;

                /*
                 * Modify the command lookup path, if a PATH= assignment
                 * is present
                 */
                for (i = 0; i < varlist.count; i++)
                        if (strncmp(varlist.args[i], PATH, sizeof(PATH) - 1) == 0) {
                                path = varlist.args[i] + sizeof(PATH) - 1;
                                /*
                                 * On `PATH=... command`, we need to make
                                 * sure that the command isn't using the
                                 * non-updated hash table of the outer PATH
                                 * setting and we need to make sure that
                                 * the hash table isn't filled with items
                                 * from the temporary setting.
                                 *
                                 * It would be better to forbid using and
                                 * updating the table while this command
                                 * runs, by the command finding mechanism
                                 * is heavily integrated with hash handling,
                                 * so we just delete the hash before and after
                                 * the command runs. Partly deleting like
                                 * changepatch() does doesn't seem worth the
                                 * booking effort, since most such runs add
                                 * directories in front of the new PATH.
                                 */
                                clearcmdentry();
                                do_clearcmdentry = 1;
                        }

                for (;;) {
                        if (bltinonly) {
                                cmdentry.u.index = find_builtin(*argv, &cmdentry.special);
                                if (cmdentry.u.index < 0) {
                                        cmdentry.u.index = BLTINCMD;
                                        argv--;
                                        argc++;
                                        break;
                                }
                        } else
                                find_command(argv[0], &cmdentry, cmd_flags, path);
                        /* implement the bltin and command builtins here */
                        if (cmdentry.cmdtype != CMDBUILTIN)
                                break;
                        if (cmdentry.u.index == BLTINCMD) {
                                if (argc == 1)
                                        break;
                                argv++;
                                argc--;
                                bltinonly = 1;
                        } else if (cmdentry.u.index == COMMANDCMD) {
                                if (argc == 1)
                                        break;
                                if (!strcmp(argv[1], "-p")) {
                                        if (argc == 2)
                                                break;
                                        if (argv[2][0] == '-') {
                                                if (strcmp(argv[2], "--"))
                                                        break;
                                                if (argc == 3)
                                                        break;
                                                argv += 3;
                                                argc -= 3;
                                        } else {
                                                argv += 2;
                                                argc -= 2;
                                        }
                                        path = _PATH_STDPATH;
                                        clearcmdentry();
                                        do_clearcmdentry = 1;
                                } else if (!strcmp(argv[1], "--")) {
                                        if (argc == 2)
                                                break;
                                        argv += 2;
                                        argc -= 2;
                                } else if (argv[1][0] == '-')
                                        break;
                                else {
                                        argv++;
                                        argc--;
                                }
                                cmd_flags |= DO_NOFUNC;
                                bltinonly = 0;
                        } else
                                break;
                }
                /*
                 * Special builtins lose their special properties when
                 * called via 'command'.
                 */
                if (cmd_flags & DO_NOFUNC)
                        cmdentry.special = 0;
        }

        /* Fork off a child process if necessary. */
        if (((cmdentry.cmdtype == CMDNORMAL || cmdentry.cmdtype == CMDUNKNOWN)
            && ((flags & EV_EXIT) == 0 || have_traps()))
         || ((flags & EV_BACKCMD) != 0
            && (cmdentry.cmdtype != CMDBUILTIN ||
                 !safe_builtin(cmdentry.u.index, argc, argv)))) {
                jp = makejob(cmd, 1);
                mode = FORK_FG;
                if (flags & EV_BACKCMD) {
                        mode = FORK_NOJOB;
                        if (pipe(pip) < 0)
                                error("Pipe call failed: %s", strerror(errno));
                }
                if (cmdentry.cmdtype == CMDNORMAL &&
                    cmd->ncmd.redirect == NULL &&
                    varlist.count == 0 &&
                    (mode == FORK_FG || mode == FORK_NOJOB) &&
                    !disvforkset() && !iflag && !mflag) {
                        vforkexecshell(jp, argv, environment(), path,
                            cmdentry.u.index, flags & EV_BACKCMD ? pip : NULL);
                        goto parent;
                }
                if (forkshell(jp, cmd, mode) != 0)
                        goto parent;    /* at end of routine */
                if (flags & EV_BACKCMD) {
                        FORCEINTON;
                        close(pip[0]);
                        if (pip[1] != 1) {
                                dup2(pip[1], 1);
                                close(pip[1]);
                        }
                        flags &= ~EV_BACKCMD;
                }
                flags |= EV_EXIT;
        }

        /* This is the child process if a fork occurred. */
        /* Execute the command. */
        if (cmdentry.cmdtype == CMDFUNCTION) {
#ifdef DEBUG
                trputs("Shell function:  ");  trargs(argv);
#endif
                saveparam = shellparam;
                shellparam.malloc = 0;
                shellparam.reset = 1;
                shellparam.nparam = argc - 1;
                shellparam.p = argv + 1;
                shellparam.optp = NULL;
                shellparam.optnext = NULL;
                INTOFF;
                savelocalvars = localvars;
                localvars = NULL;
                reffunc(cmdentry.u.func);
                savehandler = handler;
                if (setjmp(jmploc.loc)) {
                        popredir();
                        unreffunc(cmdentry.u.func);
                        poplocalvars();
                        localvars = savelocalvars;
                        freeparam(&shellparam);
                        shellparam = saveparam;
                        funcnest--;
                        handler = savehandler;
                        longjmp(handler->loc, 1);
                }
                handler = &jmploc;
                funcnest++;
                redirect(cmd->ncmd.redirect, REDIR_PUSH);
                INTON;
                for (i = 0; i < varlist.count; i++)
                        mklocal(varlist.args[i]);
                exitstatus = oexitstatus;
                evaltree(getfuncnode(cmdentry.u.func),
                    flags & (EV_TESTED | EV_EXIT));
                INTOFF;
                unreffunc(cmdentry.u.func);
                poplocalvars();
                localvars = savelocalvars;
                freeparam(&shellparam);
                shellparam = saveparam;
                handler = savehandler;
                funcnest--;
                popredir();
                INTON;
                if (evalskip == SKIPRETURN) {
                        evalskip = 0;
                        skipcount = 0;
                }
                if (jp)
                        exitshell(exitstatus);
        } else if (cmdentry.cmdtype == CMDBUILTIN) {
#ifdef DEBUG
                trputs("builtin command:  ");  trargs(argv);
#endif
                mode = (cmdentry.u.index == EXECCMD)? 0 : REDIR_PUSH;
                if (flags == EV_BACKCMD) {
                        memout.nextc = memout.buf;
                        mode |= REDIR_BACKQ;
                }
                savecmdname = commandname;
                savetopfile = getcurrentfile();
                cmdenviron = &varlist;
                e = -1;
                savehandler = handler;
                if (setjmp(jmploc.loc)) {
                        e = exception;
                        if (e == EXINT)
                                exitstatus = SIGINT+128;
                        goto cmddone;
                }
                handler = &jmploc;
                redirect(cmd->ncmd.redirect, mode);
                outclearerror(out1);
                /*
                 * If there is no command word, redirection errors should
                 * not be fatal but assignment errors should.
                 */
                if (argc == 0)
                        cmdentry.special = 1;
                listsetvar(cmdenviron, cmdentry.special ? 0 : VNOSET);
                if (argc > 0)
                        bltinsetlocale();
                commandname = argv[0];
                argptr = argv + 1;
                nextopt_optptr = NULL;          /* initialize nextopt */
                builtin_flags = flags;
                exitstatus = (*builtinfunc[cmdentry.u.index])(argc, argv);
                flushall();
                if (outiserror(out1)) {
                        warning("write error on stdout");
                        if (exitstatus == 0 || exitstatus == 1)
                                exitstatus = 2;
                }
cmddone:
                if (argc > 0)
                        bltinunsetlocale();
                cmdenviron = NULL;
                out1 = &output;
                out2 = &errout;
                freestdout();
                handler = savehandler;
                commandname = savecmdname;
                if (jp)
                        exitshell(exitstatus);
                if (flags == EV_BACKCMD) {
                        backcmd->buf = memout.buf;
                        backcmd->nleft = memout.buf != NULL ?
                            memout.nextc - memout.buf : 0;
                        memout.buf = NULL;
                        memout.nextc = NULL;
                        memout.bufend = NULL;
                        memout.bufsize = 64;
                }
                if (cmdentry.u.index != EXECCMD)
                        popredir();
                if (e != -1) {
                        if (e != EXERROR || cmdentry.special)
                                exraise(e);
                        popfilesupto(savetopfile);
                        if (flags != EV_BACKCMD)
                                FORCEINTON;
                }
        } else {
#ifdef DEBUG
                trputs("normal command:  ");  trargs(argv);
#endif
                redirect(cmd->ncmd.redirect, 0);
                for (i = 0; i < varlist.count; i++)
                        setvareq(varlist.args[i], VEXPORT|VSTACK);
                envp = environment();
                shellexec(argv, envp, path, cmdentry.u.index);
                /*NOTREACHED*/
        }
        goto out;

parent: /* parent process gets here (if we forked) */
        if (mode == FORK_FG) {  /* argument to fork */
                INTOFF;
                exitstatus = waitforjob(jp, &signaled);
                INTON;
                if (iflag && loopnest > 0 && signaled) {
                        evalskip = SKIPBREAK;
                        skipcount = loopnest;
                }
        } else if (mode == FORK_NOJOB) {
                backcmd->fd = pip[0];
                close(pip[1]);
                backcmd->jp = jp;
        }

out:
        if (lastarg)
                setvar("_", lastarg, 0);
        if (do_clearcmdentry)
                clearcmdentry();
}



/*
 * Search for a command.  This is called before we fork so that the
 * location of the command will be available in the parent as well as
 * the child.  The check for "goodname" is an overly conservative
 * check that the name will not be subject to expansion.
 */

static void
prehash(union node *n)
{
        struct cmdentry entry;

        if (n && n->type == NCMD && n->ncmd.args)
                if (goodname(n->ncmd.args->narg.text))
                        find_command(n->ncmd.args->narg.text, &entry, 0,
                                     pathval());
}



/*
 * Builtin commands.  Builtin commands whose functions are closely
 * tied to evaluation are implemented here.
 */

/*
 * No command given, a bltin command with no arguments, or a bltin command
 * with an invalid name.
 */

int
bltincmd(int argc, char **argv)
{
        if (argc > 1) {
                out2fmt_flush("%s: not found\n", argv[1]);
                return 127;
        }
        /*
         * Preserve exitstatus of a previous possible command substitution
         * as POSIX mandates
         */
        return exitstatus;
}


/*
 * Handle break and continue commands.  Break, continue, and return are
 * all handled by setting the evalskip flag.  The evaluation routines
 * above all check this flag, and if it is set they start skipping
 * commands rather than executing them.  The variable skipcount is
 * the number of loops to break/continue, or the number of function
 * levels to return.  (The latter is always 1.)  It should probably
 * be an error to break out of more loops than exist, but it isn't
 * in the standard shell so we don't make it one here.
 */

int
breakcmd(int argc, char **argv)
{
        long n;
        char *end;

        if (argc > 1) {
                /* Allow arbitrarily large numbers. */
                n = strtol(argv[1], &end, 10);
                if (!is_digit(argv[1][0]) || *end != '\0')
                        error("Illegal number: %s", argv[1]);
        } else
                n = 1;
        if (n > loopnest)
                n = loopnest;
        if (n > 0) {
                evalskip = (**argv == 'c')? SKIPCONT : SKIPBREAK;
                skipcount = n;
        }
        return 0;
}

/*
 * The `command' command.
 */
int
commandcmd(int argc __unused, char **argv __unused)
{
        const char *path;
        int ch;
        int cmd = -1;

        path = bltinlookup("PATH", 1);

        while ((ch = nextopt("pvV")) != '\0') {
                switch (ch) {
                case 'p':
                        path = _PATH_STDPATH;
                        break;
                case 'v':
                        cmd = TYPECMD_SMALLV;
                        break;
                case 'V':
                        cmd = TYPECMD_BIGV;
                        break;
                }
        }

        if (cmd != -1) {
                if (*argptr == NULL || argptr[1] != NULL)
                        error("wrong number of arguments");
                return typecmd_impl(2, argptr - 1, cmd, path);
        }
        if (*argptr != NULL)
                error("commandcmd bad call");

        /*
         * Do nothing successfully if no command was specified;
         * ksh also does this.
         */
        return 0;
}


/*
 * The return command.
 */

int
returncmd(int argc, char **argv)
{
        int ret = argc > 1 ? number(argv[1]) : oexitstatus;

        evalskip = SKIPRETURN;
        skipcount = 1;
        return ret;
}


int
falsecmd(int argc __unused, char **argv __unused)
{
        return 1;
}


int
truecmd(int argc __unused, char **argv __unused)
{
        return 0;
}


int
execcmd(int argc, char **argv)
{
        int i;

        /*
         * Because we have historically not supported any options,
         * only treat "--" specially.
         */
        if (argc > 1 && strcmp(argv[1], "--") == 0)
                argc--, argv++;
        if (argc > 1) {
                iflag = 0;              /* exit on error */
                mflag = 0;
                optschanged();
                for (i = 0; i < cmdenviron->count; i++)
                        setvareq(cmdenviron->args[i], VEXPORT|VSTACK);
                shellexec(argv + 1, environment(), pathval(), 0);

        }
        return 0;
}


int
timescmd(int argc __unused, char **argv __unused)
{
        struct rusage ru;
        long shumins, shsmins, chumins, chsmins;
        double shusecs, shssecs, chusecs, chssecs;

        if (getrusage(RUSAGE_SELF, &ru) < 0)
                return 1;
        shumins = ru.ru_utime.tv_sec / 60;
        shusecs = ru.ru_utime.tv_sec % 60 + ru.ru_utime.tv_usec / 1000000.;
        shsmins = ru.ru_stime.tv_sec / 60;
        shssecs = ru.ru_stime.tv_sec % 60 + ru.ru_stime.tv_usec / 1000000.;
        if (getrusage(RUSAGE_CHILDREN, &ru) < 0)
                return 1;
        chumins = ru.ru_utime.tv_sec / 60;
        chusecs = ru.ru_utime.tv_sec % 60 + ru.ru_utime.tv_usec / 1000000.;
        chsmins = ru.ru_stime.tv_sec / 60;
        chssecs = ru.ru_stime.tv_sec % 60 + ru.ru_stime.tv_usec / 1000000.;
        out1fmt("%ldm%.3fs %ldm%.3fs\n%ldm%.3fs %ldm%.3fs\n", shumins,
            shusecs, shsmins, shssecs, chumins, chusecs, chsmins, chssecs);
        return 0;
}