jobs.c

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/*-
 * Copyright (c) 1991 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. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by the University of
 *      California, Berkeley and its contributors.
 * 4. 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.
 */

#ifndef lint
static char sccsid[] = "@(#)jobs.c      5.1 (Berkeley) 3/7/91";
#endif /* not lint */

#include "shell.h"
#if JOBS
#include "sgtty.h"
#undef CEOF                     /* syntax.h redefines this */
#endif
#include "main.h"
#include "parser.h"
#include "nodes.h"
#include "jobs.h"
#include "options.h"
#include "trap.h"
#include "signames.h"
#include "syntax.h"
#include "input.h"
#include "output.h"
#include "memalloc.h"
#include "error.h"
#include "mystring.h"
#include "redir.h"
#include <sys/types.h>
#include <fcntl.h>
#include <signal.h>
#include <errno.h>
#ifdef BSD
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/time.h>
#include <sys/resource.h>
#endif
#if POSIX
#include <sys/wait.h>
#endif



struct job *jobtab;             /* array of jobs */
int njobs;                      /* size of array */
MKINIT pid_t backgndpid = -1;   /* pid of last background process */
#if JOBS
int initialpgrp;                /* pgrp of shell on invocation */
pid_t curjob;                   /* current job */
#endif

#ifdef __STDC__
STATIC void restartjob(struct job *);
STATIC struct job *getjob(char *);
STATIC void freejob(struct job *);
STATIC int procrunning(int);
STATIC int dowait(int, struct job *);
STATIC int waitproc(int, int *);
STATIC char *commandtext(union node *);
#else
STATIC void restartjob();
STATIC struct job *getjob();
STATIC void freejob();
STATIC int procrunning();
STATIC int dowait();
STATIC int waitproc();
STATIC char *commandtext();
#endif


 
#if JOBS
/*
 * Turn job control on and off.
 *
 * Note:  This code assumes that the third arg to ioctl is a character
 * pointer, which is true on Berkeley systems but not System V.  Since
 * System V doesn't have job control yet, this isn't a problem now.
 */

MKINIT int jobctl;

void
setjobctl(on) {
        int ldisc;

        if (on == jobctl || rootshell == 0)
                return;
        if (on) {
                do { /* while we are in the background */
                        if (ioctl(2, TIOCGPGRP, (char *)&initialpgrp) < 0) {
                                out2str("ash: can't access tty; job control turned off\n");
                                jflag = 0;
                                return;
                        }
                        if (initialpgrp == -1)
                                initialpgrp = getpgrp(0);
                        else if (initialpgrp != getpgrp(0)) {
                                killpg(initialpgrp, SIGTTIN);
                                continue;
                        }
                } while (0);
                if (ioctl(2, TIOCGETD, (char *)&ldisc) < 0 || ldisc != NTTYDISC) {
                        out2str("ash: need new tty driver to run job control; job control turned off\n");
                        jflag = 0;
                        return;
                }
                setsignal(SIGTSTP);
                setsignal(SIGTTOU);
                setpgrp(0, rootpid);
                ioctl(2, TIOCSPGRP, (char *)&rootpid);
        } else { /* turning job control off */
                setpgrp(0, initialpgrp);
                ioctl(2, TIOCSPGRP, (char *)&initialpgrp);
                setsignal(SIGTSTP);
                setsignal(SIGTTOU);
        }
        jobctl = on;
}
#endif


#ifdef mkinit

SHELLPROC {
        backgndpid = -1;
#if JOBS
        jobctl = 0;
#endif
}

#endif



#if JOBS
fgcmd(argc, argv)  char **argv; {
        struct job *jp;
        int pgrp;
        int status;

        jp = getjob(argv[1]);
        if (jp->jobctl == 0)
                error("job not created under job control");
        pgrp = jp->ps[0].pid;
        ioctl(2, TIOCSPGRP, (char *)&pgrp);
        restartjob(jp);
        INTOFF;
        status = waitforjob(jp);
        INTON;
        return status;
}


bgcmd(argc, argv)  char **argv; {
        struct job *jp;

        do {
                jp = getjob(*++argv);
                if (jp->jobctl == 0)
                        error("job not created under job control");
                restartjob(jp);
        } while (--argc > 1);
        return 0;
}


STATIC void
restartjob(jp)
        struct job *jp;
        {
        struct procstat *ps;
        int i;

        if (jp->state == JOBDONE)
                return;
        INTOFF;
        killpg(jp->ps[0].pid, SIGCONT);
        for (ps = jp->ps, i = jp->nprocs ; --i >= 0 ; ps++) {
                if ((ps->status & 0377) == 0177) {
                        ps->status = -1;
                        jp->state = 0;
                }
        }
        INTON;
}
#endif


int
jobscmd(argc, argv)  char **argv; {
        showjobs(0);
        return 0;
}


/*
 * Print a list of jobs.  If "change" is nonzero, only print jobs whose
 * statuses have changed since the last call to showjobs.
 *
 * If the shell is interrupted in the process of creating a job, the
 * result may be a job structure containing zero processes.  Such structures
 * will be freed here.
 */

void
showjobs(change) {
        int jobno;
        int procno;
        int i;
        struct job *jp;
        struct procstat *ps;
        int col;
        char s[64];

        TRACE(("showjobs(%d) called\n", change));
        while (dowait(0, (struct job *)NULL) > 0);
        for (jobno = 1, jp = jobtab ; jobno <= njobs ; jobno++, jp++) {
                if (! jp->used)
                        continue;
                if (jp->nprocs == 0) {
                        freejob(jp);
                        continue;
                }
                if (change && ! jp->changed)
                        continue;
                procno = jp->nprocs;
                for (ps = jp->ps ; ; ps++) {    /* for each process */
                        if (ps == jp->ps)
                                fmtstr(s, 64, "[%d] %d ", jobno, ps->pid);
                        else
                                fmtstr(s, 64, "    %d ", ps->pid);
                        out1str(s);
                        col = strlen(s);
                        s[0] = '\0';
                        if (ps->status == -1) {
                                /* don't print anything */
                        } else if ((ps->status & 0xFF) == 0) {
                                fmtstr(s, 64, "Exit %d", ps->status >> 8);
                        } else {
                                i = ps->status;
#if JOBS
                                if ((i & 0xFF) == 0177)
                                        i >>= 8;
#endif
                                if ((i & 0x7F) <= MAXSIG && sigmesg[i & 0x7F])
                                        scopy(sigmesg[i & 0x7F], s);
                                else
                                        fmtstr(s, 64, "Signal %d", i & 0x7F);
                                if (i & 0x80)
                                        strcat(s, " (core dumped)");
                        }
                        out1str(s);
                        col += strlen(s);
                        do {
                                out1c(' ');
                                col++;
                        } while (col < 30);
                        out1str(ps->cmd);
                        out1c('\n');
                        if (--procno <= 0)
                                break;
                }
                jp->changed = 0;
                if (jp->state == JOBDONE) {
                        freejob(jp);
                }
        }
}


/*
 * Mark a job structure as unused.
 */

STATIC void
freejob(jp)
        struct job *jp;
        {
        struct procstat *ps;
        int i;

        INTOFF;
        for (i = jp->nprocs, ps = jp->ps ; --i >= 0 ; ps++) {
                if (ps->cmd != nullstr)
                        ckfree(ps->cmd);
        }
        if (jp->ps != &jp->ps0)
                ckfree(jp->ps);
        jp->used = 0;
#if JOBS
        if (curjob == jp - jobtab + 1)
                curjob = 0;
#endif
        INTON;
}



int
waitcmd(argc, argv)  char **argv; {
        struct job *job;
        int status;
        struct job *jp;

        if (argc > 1) {
                job = getjob(argv[1]);
        } else {
                job = NULL;
        }
        for (;;) {      /* loop until process terminated or stopped */
                if (job != NULL) {
                        if (job->state) {
                                status = job->ps[job->nprocs - 1].status;
                                if ((status & 0xFF) == 0)
                                        status = status >> 8 & 0xFF;
#if JOBS
                                else if ((status & 0xFF) == 0177)
                                        status = (status >> 8 & 0x7F) + 128;
#endif
                                else
                                        status = (status & 0x7F) + 128;
                                if (! iflag)
                                        freejob(job);
                                return status;
                        }
                } else {
                        for (jp = jobtab ; ; jp++) {
                                if (jp >= jobtab + njobs) {     /* no running procs */
                                        return 0;
                                }
                                if (jp->used && jp->state == 0)
                                        break;
                        }
                }
                dowait(1, (struct job *)NULL);
        }
}



jobidcmd(argc, argv)  char **argv; {
        struct job *jp;
        int i;

        jp = getjob(argv[1]);
        for (i = 0 ; i < jp->nprocs ; ) {
                out1fmt("%d", jp->ps[i].pid);
                out1c(++i < jp->nprocs? ' ' : '\n');
        }
        return 0;
}



/*
 * Convert a job name to a job structure.
 */

STATIC struct job *
getjob(name)
        char *name;
        {
        int jobno;
        register struct job *jp;
        int pid;
        int i;

        if (name == NULL) {
#if JOBS
currentjob:
                if ((jobno = curjob) == 0 || jobtab[jobno - 1].used == 0)
                        error("No current job");
                return &jobtab[jobno - 1];
#else
                error("No current job");
#endif
        } else if (name[0] == '%') {
                if (is_digit(name[1])) {
                        jobno = number(name + 1);
                        if (jobno > 0 && jobno <= njobs
                         && jobtab[jobno - 1].used != 0)
                                return &jobtab[jobno - 1];
#if JOBS
                } else if (name[1] == '%' && name[2] == '\0') {
                        goto currentjob;
#endif
                } else {
                        register struct job *found = NULL;
                        for (jp = jobtab, i = njobs ; --i >= 0 ; jp++) {
                                if (jp->used && jp->nprocs > 0
                                 && prefix(name + 1, jp->ps[0].cmd)) {
                                        if (found)
                                                error("%s: ambiguous", name);
                                        found = jp;
                                }
                        }
                        if (found)
                                return found;
                }
        } else if (is_number(name)) {
                pid = number(name);
                for (jp = jobtab, i = njobs ; --i >= 0 ; jp++) {
                        if (jp->used && jp->nprocs > 0
                         && jp->ps[jp->nprocs - 1].pid == pid)
                                return jp;
                }
        }
        error("No such job: %s", name);
}



/*
 * Return a new job structure,
 */

struct job *
makejob(node, nprocs)
        union node *node;
        {
        int i;
        struct job *jp;

        for (i = njobs, jp = jobtab ; ; jp++) {
                if (--i < 0) {
                        INTOFF;
                        if (njobs == 0) {
                                jobtab = ckmalloc(4 * sizeof jobtab[0]);
                        } else {
                                jp = ckmalloc((njobs + 4) * sizeof jobtab[0]);
                                bcopy(jobtab, jp, njobs * sizeof jp[0]);
                                for (i= 0; i<njobs; i++)
                                {
                                        if (jobtab[i].ps == &jobtab[i].ps0)
                                                jp[i].ps= &jp[i].ps0;
                                }
                                ckfree(jobtab);
                                jobtab = jp;
                        }
                        jp = jobtab + njobs;
                        for (i = 4 ; --i >= 0 ; jobtab[njobs++].used = 0);
                        INTON;
                        break;
                }
                if (jp->used == 0)
                        break;
        }
        INTOFF;
        jp->state = 0;
        jp->used = 1;
        jp->changed = 0;
        jp->nprocs = 0;
#if JOBS
        jp->jobctl = jobctl;
#endif
        if (nprocs > 1) {
                jp->ps = ckmalloc(nprocs * sizeof (struct procstat));
        } else {
                jp->ps = &jp->ps0;
        }
        INTON;
        TRACE(("makejob(0x%x, %d) returns %%%d\n", (int)node, nprocs, jp - jobtab + 1));
        return jp;
}       


/*
 * Fork of a subshell.  If we are doing job control, give the subshell its
 * own process group.  Jp is a job structure that the job is to be added to.
 * N is the command that will be evaluated by the child.  Both jp and n may
 * be NULL.  The mode parameter can be one of the following:
 *      FORK_FG - Fork off a foreground process.
 *      FORK_BG - Fork off a background process.
 *      FORK_NOJOB - Like FORK_FG, but don't give the process its own
 *                   process group even if job control is on.
 *
 * When job control is turned off, background processes have their standard
 * input redirected to /dev/null (except for the second and later processes
 * in a pipeline).
 */

int
forkshell(jp, n, mode)
        union node *n;
        struct job *jp;
        {
        int pid;
        int pgrp;

        TRACE(("forkshell(%%%d, 0x%x, %d) called\n", jp - jobtab, (int)n, mode));
        INTOFF;
        pid = fork();
        if (pid == -1) {
                TRACE(("Fork failed, errno=%d\n", errno));
                INTON;
                error("Cannot fork");
        }
        if (pid == 0) {
                struct job *p;
                int wasroot;
                int i;

                TRACE(("Child shell %d\n", getpid()));
                wasroot = rootshell;
                rootshell = 0;
                for (i = njobs, p = jobtab ; --i >= 0 ; p++)
                        if (p->used)
                                freejob(p);
                closescript();
                INTON;
                clear_traps();
#if JOBS
                jobctl = 0;             /* do job control only in root shell */
                if (wasroot && mode != FORK_NOJOB && jflag) {
                        if (jp == NULL || jp->nprocs == 0)
                                pgrp = getpid();
                        else
                                pgrp = jp->ps[0].pid;
                        setpgrp(0, pgrp);
                        if (mode == FORK_FG) {
                                /*** this causes superfluous TIOCSPGRPS ***/
                                if (ioctl(2, TIOCSPGRP, (char *)&pgrp) < 0)
                                        error("TIOCSPGRP failed, errno=%d\n", errno);
                        }
                        setsignal(SIGTSTP);
                        setsignal(SIGTTOU);
                } else if (mode == FORK_BG) {
                        ignoresig(SIGINT);
                        ignoresig(SIGQUIT);
                        if ((jp == NULL || jp->nprocs == 0)
                            && ! fd0_redirected_p ()) {
                                close(0);
                                if (open("/dev/null", O_RDONLY) != 0)
                                        error("Can't open /dev/null");
                        }
                }
#else
                if (mode == FORK_BG) {
                        ignoresig(SIGINT);
                        ignoresig(SIGQUIT);
                        if ((jp == NULL || jp->nprocs == 0)
                            && ! fd0_redirected_p ()) {
                                close(0);
                                if (open("/dev/null", O_RDONLY) != 0)
                                        error("Can't open /dev/null");
                        }
                }
#endif
                if (wasroot && iflag) {
                        setsignal(SIGINT);
                        setsignal(SIGQUIT);
                        setsignal(SIGTERM);
                }
                return pid;
        }
        if (rootshell && mode != FORK_NOJOB && jflag) {
                if (jp == NULL || jp->nprocs == 0)
                        pgrp = pid;
                else
                        pgrp = jp->ps[0].pid;
#if JOBS
                setpgrp(pid, pgrp);
#endif
        }
        if (mode == FORK_BG)
                backgndpid = pid;               /* set $! */
        if (jp) {
                struct procstat *ps = &jp->ps[jp->nprocs++];
                ps->pid = pid;
                ps->status = -1;
                ps->cmd = nullstr;
                if (iflag && rootshell && n)
                        ps->cmd = commandtext(n);
        }
        INTON;
        TRACE(("In parent shell:  child = %d\n", pid));
        return pid;
}



/*
 * Wait for job to finish.
 *
 * Under job control we have the problem that while a child process is
 * running interrupts generated by the user are sent to the child but not
 * to the shell.  This means that an infinite loop started by an inter-
 * active user may be hard to kill.  With job control turned off, an
 * interactive user may place an interactive program inside a loop.  If
 * the interactive program catches interrupts, the user doesn't want
 * these interrupts to also abort the loop.  The approach we take here
 * is to have the shell ignore interrupt signals while waiting for a
 * forground process to terminate, and then send itself an interrupt
 * signal if the child process was terminated by an interrupt signal.
 * Unfortunately, some programs want to do a bit of cleanup and then
 * exit on interrupt; unless these processes terminate themselves by
 * sending a signal to themselves (instead of calling exit) they will
 * confuse this approach.
 */

int
waitforjob(jp)
        register struct job *jp;
        {
#if JOBS
        int mypgrp = getpgrp(0);
#endif
        int status;
        int st;

        INTOFF;
        TRACE(("waitforjob(%%%d) called\n", jp - jobtab + 1));
        while (jp->state == 0 && dowait(1, jp) != -1) ;
#if JOBS
        if (jp->jobctl) {
                if (ioctl(2, TIOCSPGRP, (char *)&mypgrp) < 0)
                        error("TIOCSPGRP failed, errno=%d\n", errno);
        }
        if (jp->state == JOBSTOPPED)
                curjob = jp - jobtab + 1;
#endif
        status = jp->ps[jp->nprocs - 1].status;
        /* convert to 8 bits */
        if ((status & 0xFF) == 0)
                st = status >> 8 & 0xFF;
#if JOBS
        else if ((status & 0xFF) == 0177)
                st = (status >> 8 & 0x7F) + 128;
#endif
        else
                st = (status & 0x7F) + 128;
        if (! JOBS || jp->state == JOBDONE)
                freejob(jp);
        CLEAR_PENDING_INT;
        if ((status & 0x7F) == SIGINT)
                kill(getpid(), SIGINT);
        INTON;
        return st;
}



/*
 * Wait for a process to terminate.
 */

STATIC int
dowait(block, job)
        struct job *job;
        {
        int pid;
        int status;
        struct procstat *sp;
        struct job *jp;
        struct job *thisjob;
        int done;
        int stopped;
        int core;

        TRACE(("dowait(%d) called\n", block));
        do {
                pid = waitproc(block, &status);
                TRACE(("wait returns %d, status=%d, errno=%d\n",
                                pid, status, errno));
        } while (pid == -1 && errno == EINTR);
        if (pid <= 0)
                return pid;
        INTOFF;
        thisjob = NULL;
        for (jp = jobtab ; jp < jobtab + njobs ; jp++) {
                if (jp->used) {
                        done = 1;
                        stopped = 1;
                        for (sp = jp->ps ; sp < jp->ps + jp->nprocs ; sp++) {
                                if (sp->pid == -1)
                                        continue;
                                if (sp->pid == pid) {
                                        TRACE(("Changin status of proc %d from 0x%x to 0x%x\n", pid, sp->status, status));
                                        sp->status = status;
                                        thisjob = jp;
                                }
                                if (sp->status == -1)
                                        stopped = 0;
                                else if ((sp->status & 0377) == 0177)
                                        done = 0;
                        }
                        if (stopped) {          /* stopped or done */
                                int state = done? JOBDONE : JOBSTOPPED;
                                if (jp->state != state) {
                                        TRACE(("Job %d: changing state from %d to %d\n", jp - jobtab + 1, jp->state, state));
                                        jp->state = state;
#if JOBS
                                        if (done && curjob == jp - jobtab + 1)
                                                curjob = 0;             /* no current job */
#endif
                                }
                        }
                }
        }
        INTON;
        if (! rootshell || ! iflag || (job && thisjob == job)) {
#if JOBS
                if ((status & 0xFF) == 0177)
                        status >>= 8;
#endif
                core = status & 0x80;
                status &= 0x7F;
                if (status != 0 && status != SIGINT && status != SIGPIPE) {
                        if (thisjob != job)
                                outfmt(out2, "%d: ", pid);
#if JOBS
                        if (status == SIGTSTP && rootshell && iflag)
                                outfmt(out2, "%%%d ", job - jobtab + 1);
#endif
                        if (status <= MAXSIG && sigmesg[status])
                                out2str(sigmesg[status]);
                        else
                                outfmt(out2, "Signal %d", status);
                        if (core)
                                out2str(" - core dumped");
                        out2c('\n');
                        flushout(&errout);
                } else {
                        TRACE(("Not printing status: status=%d\n", status));
                }
        } else {
                TRACE(("Not printing status, rootshell=%d, job=0x%x\n", rootshell, job));
                if (thisjob)
                        thisjob->changed = 1;
        }
        return pid;
}



/*
 * Do a wait system call.  If job control is compiled in, we accept
 * stopped processes.  If block is zero, we return a value of zero
 * rather than blocking.
 *
 * System V doesn't have a non-blocking wait system call.  It does
 * have a SIGCLD signal that is sent to a process when one of it's
 * children dies.  The obvious way to use SIGCLD would be to install
 * a handler for SIGCLD which simply bumped a counter when a SIGCLD
 * was received, and have waitproc bump another counter when it got
 * the status of a process.  Waitproc would then know that a wait
 * system call would not block if the two counters were different.
 * This approach doesn't work because if a process has children that
 * have not been waited for, System V will send it a SIGCLD when it
 * installs a signal handler for SIGCLD.  What this means is that when
 * a child exits, the shell will be sent SIGCLD signals continuously
 * until is runs out of stack space, unless it does a wait call before
 * restoring the signal handler.  The code below takes advantage of
 * this (mis)feature by installing a signal handler for SIGCLD and
 * then checking to see whether it was called.  If there are any
 * children to be waited for, it will be.
 *
 * If neither SYSV nor BSD is defined, we don't implement nonblocking
 * waits at all.  In this case, the user will not be informed when
 * a background process until the next time she runs a real program
 * (as opposed to running a builtin command or just typing return),
 * and the jobs command may give out of date information.
 */

#ifdef SYSV
STATIC int gotsigchild;

STATIC int onsigchild() {
        gotsigchild = 1;
}
#endif


STATIC int
waitproc(block, status)
        int *status;
        {
#ifdef BSD
        int flags;

#if JOBS
        flags = WUNTRACED;
#else
        flags = 0;
#endif
        if (block == 0)
                flags |= WNOHANG;
        return wait3((union wait *)status, flags, (struct rusage *)NULL);
#else
#ifdef SYSV
        int (*save)();

        if (block == 0) {
                gotsigchild = 0;
                save = signal(SIGCLD, onsigchild);
                signal(SIGCLD, save);
                if (gotsigchild == 0)
                        return 0;
        }
        return wait(status);
#else
#if POSIX
        return waitpid(-1, status, block == 0 ? WNOHANG : 0);
#else
        if (block == 0)
                return 0;
        return wait(status);
#endif
#endif
#endif
}



/*
 * Return a string identifying a command (to be printed by the
 * jobs command.
 */

STATIC char *cmdnextc;
STATIC int cmdnleft;
STATIC void cmdtxt(), cmdputs();

STATIC char *
commandtext(n)
        union node *n;
        {
        char *name;

        cmdnextc = name = ckmalloc(50);
        cmdnleft = 50 - 4;
        cmdtxt(n);
        *cmdnextc = '\0';
        return name;
}


STATIC void
cmdtxt(n)
        union node *n;
        {
        union node *np;
        struct nodelist *lp;
        char *p;
        int i;
        char s[2];

        if (n == NULL) return;

        switch (n->type) {
        case NSEMI:
                cmdtxt(n->nbinary.ch1);
                cmdputs("; ");
                cmdtxt(n->nbinary.ch2);
                break;
        case NAND:
                cmdtxt(n->nbinary.ch1);
                cmdputs(" && ");
                cmdtxt(n->nbinary.ch2);
                break;
        case NOR:
                cmdtxt(n->nbinary.ch1);
                cmdputs(" || ");
                cmdtxt(n->nbinary.ch2);
                break;
        case NPIPE:
                for (lp = n->npipe.cmdlist ; lp ; lp = lp->next) {
                        cmdtxt(lp->n);
                        if (lp->next)
                                cmdputs(" | ");
                }
                break;
        case NSUBSHELL:
                cmdputs("(");
                cmdtxt(n->nredir.n);
                cmdputs(")");
                break;
        case NREDIR:
        case NBACKGND:
                cmdtxt(n->nredir.n);
                break;
        case NIF:
                cmdputs("if ");
                cmdtxt(n->nif.test);
                cmdputs("; then ");
                cmdtxt(n->nif.ifpart);
                cmdputs("...");
                break;
        case NWHILE:
                cmdputs("while ");
                goto until;
        case NUNTIL:
                cmdputs("until ");
until:
                cmdtxt(n->nbinary.ch1);
                cmdputs("; do ");
                cmdtxt(n->nbinary.ch2);
                cmdputs("; done");
                break;
        case NFOR:
                cmdputs("for ");
                cmdputs(n->nfor.var);
                cmdputs(" in ...");
                break;
        case NCASE:
                cmdputs("case ");
                cmdputs(n->ncase.expr->narg.text);
                cmdputs(" in ...");
                break;
        case NDEFUN:
                cmdputs(n->narg.text);
                cmdputs("() ...");
                break;
        case NCMD:
                for (np = n->ncmd.args ; np ; np = np->narg.next) {
                        cmdtxt(np);
                        if (np->narg.next)
                                cmdputs(" ");
                }
                for (np = n->ncmd.redirect ; np ; np = np->nfile.next) {
                        cmdputs(" ");
                        cmdtxt(np);
                }
                break;
        case NARG:
                cmdputs(n->narg.text);
                break;
        case NTO:
                p = ">";  i = 1;  goto redir;
        case NAPPEND:
                p = ">>";  i = 1;  goto redir;
        case NTOFD:
                p = ">&";  i = 1;  goto redir;
        case NFROM:
                p = "<";  i = 0;  goto redir;
        case NFROMFD:
                p = "<&";  i = 0;  goto redir;
redir:
                if (n->nfile.fd != i) {
                        s[0] = n->nfile.fd + '0';
                        s[1] = '\0';
                        cmdputs(s);
                }
                cmdputs(p);
                if (n->type == NTOFD || n->type == NFROMFD) {
                        s[0] = n->ndup.dupfd + '0';
                        s[1] = '\0';
                        cmdputs(s);
                } else {
                        cmdtxt(n->nfile.fname);
                }
                break;
        case NHERE:
        case NXHERE:
                cmdputs("<<...");
                break;
        default:
                cmdputs("???");
                break;
        }
}



STATIC void
cmdputs(s)
        char *s;
        {
        register char *p, *q;
        register char c;
        int subtype = 0;

        if (cmdnleft <= 0)
                return;
        p = s;
        q = cmdnextc;
        while ((c = *p++) != '\0') {
                if (c == CTLESC)
                        *q++ = *p++;
                else if (c == CTLVAR) {
                        *q++ = '$';
                        if (--cmdnleft > 0)
                                *q++ = '{';
                        subtype = *p++;
                } else if (c == '=' && subtype != 0) {
                        *q++ = "}-+?="[(subtype & VSTYPE) - VSNORMAL];
                        subtype = 0;
                } else if (c == CTLENDVAR) {
                        *q++ = '}';
                } else if (c == CTLBACKQ | c == CTLBACKQ+CTLQUOTE)
                        cmdnleft++;             /* ignore it */
                else
                        *q++ = c;
                if (--cmdnleft <= 0) {
                        *q++ = '.';
                        *q++ = '.';
                        *q++ = '.';
                        break;
                }
        }
        cmdnextc = q;
}

---