source: downloads/tcl8.5.2/generic/tclPipe.c @ 63

/*
 * tclPipe.c --
 *
 *      This file contains the generic portion of the command channel driver
 *      as well as various utility routines used in managing subprocesses.
 *
 * Copyright (c) 1997 by Sun Microsystems, Inc.
 *
 * See the file "license.terms" for information on usage and redistribution of
 * this file, and for a DISCLAIMER OF ALL WARRANTIES.
 *
 * RCS: @(#) $Id: tclPipe.c,v 1.19 2007/04/20 06:10:58 kennykb Exp $
 */

#include "tclInt.h"

/*
 * A linked list of the following structures is used to keep track of child
 * processes that have been detached but haven't exited yet, so we can make
 * sure that they're properly "reaped" (officially waited for) and don't lie
 * around as zombies cluttering the system.
 */

typedef struct Detached {
    Tcl_Pid pid;                /* Id of process that's been detached but
                                 * isn't known to have exited. */
    struct Detached *nextPtr;   /* Next in list of all detached processes. */
} Detached;

static Detached *detList = NULL;/* List of all detached proceses. */
TCL_DECLARE_MUTEX(pipeMutex)    /* Guard access to detList. */

/*
 * Declarations for local functions defined in this file:
 */

static TclFile          FileForRedirect(Tcl_Interp *interp, CONST char *spec,
                            int atOk, CONST char *arg, CONST char *nextArg,
                            int flags, int *skipPtr, int *closePtr,
                            int *releasePtr);

/*
 *----------------------------------------------------------------------
 *
 * FileForRedirect --
 *
 *      This function does much of the work of parsing redirection operators.
 *      It handles "@" if specified and allowed, and a file name, and opens
 *      the file if necessary.
 *
 * Results:
 *      The return value is the descriptor number for the file. If an error
 *      occurs then NULL is returned and an error message is left in the
 *      interp's result. Several arguments are side-effected; see the argument
 *      list below for details.
 *
 * Side effects:
 *      None.
 *
 *----------------------------------------------------------------------
 */

static TclFile
FileForRedirect(
    Tcl_Interp *interp,         /* Intepreter to use for error reporting. */
    CONST char *spec,           /* Points to character just after redirection
                                 * character. */
    int atOK,                   /* Non-zero means that '@' notation can be
                                 * used to specify a channel, zero means that
                                 * it isn't. */
    CONST char *arg,            /* Pointer to entire argument containing spec:
                                 * used for error reporting. */
    CONST char *nextArg,        /* Next argument in argc/argv array, if needed
                                 * for file name or channel name. May be
                                 * NULL. */
    int flags,                  /* Flags to use for opening file or to specify
                                 * mode for channel. */
    int *skipPtr,               /* Filled with 1 if redirection target was in
                                 * spec, 2 if it was in nextArg. */
    int *closePtr,              /* Filled with one if the caller should close
                                 * the file when done with it, zero
                                 * otherwise. */
    int *releasePtr)
{
    int writing = (flags & O_WRONLY);
    Tcl_Channel chan;
    TclFile file;

    *skipPtr = 1;
    if ((atOK != 0) && (*spec == '@')) {
        spec++;
        if (*spec == '\0') {
            spec = nextArg;
            if (spec == NULL) {
                goto badLastArg;
            }
            *skipPtr = 2;
        }
        chan = Tcl_GetChannel(interp, spec, NULL);
        if (chan == (Tcl_Channel) NULL) {
            return NULL;
        }
        file = TclpMakeFile(chan, writing ? TCL_WRITABLE : TCL_READABLE);
        if (file == NULL) {
            Tcl_AppendResult(interp, "channel \"", Tcl_GetChannelName(chan),
                    "\" wasn't opened for ",
                    ((writing) ? "writing" : "reading"), NULL);
            return NULL;
        }
        *releasePtr = 1;
        if (writing) {
            /*
             * Be sure to flush output to the file, so that anything written
             * by the child appears after stuff we've already written.
             */

            Tcl_Flush(chan);
        }
    } else {
        CONST char *name;
        Tcl_DString nameString;

        if (*spec == '\0') {
            spec = nextArg;
            if (spec == NULL) {
                goto badLastArg;
            }
            *skipPtr = 2;
        }
        name = Tcl_TranslateFileName(interp, spec, &nameString);
        if (name == NULL) {
            return NULL;
        }
        file = TclpOpenFile(name, flags);
        Tcl_DStringFree(&nameString);
        if (file == NULL) {
            Tcl_AppendResult(interp, "couldn't ",
                    ((writing) ? "write" : "read"), " file \"", spec, "\": ",
                    Tcl_PosixError(interp), NULL);
            return NULL;
        }
        *closePtr = 1;
    }
    return file;

  badLastArg:
    Tcl_AppendResult(interp, "can't specify \"", arg,
            "\" as last word in command", NULL);
    return NULL;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_DetachPids --
 *
 *      This function is called to indicate that one or more child processes
 *      have been placed in background and will never be waited for; they
 *      should eventually be reaped by Tcl_ReapDetachedProcs.
 *
 * Results:
 *      None.
 *
 * Side effects:
 *      None.
 *
 *----------------------------------------------------------------------
 */

void
Tcl_DetachPids(
    int numPids,                /* Number of pids to detach: gives size of
                                 * array pointed to by pidPtr. */
    Tcl_Pid *pidPtr)            /* Array of pids to detach. */
{
    register Detached *detPtr;
    int i;

    Tcl_MutexLock(&pipeMutex);
    for (i = 0; i < numPids; i++) {
        detPtr = (Detached *) ckalloc(sizeof(Detached));
        detPtr->pid = pidPtr[i];
        detPtr->nextPtr = detList;
        detList = detPtr;
    }
    Tcl_MutexUnlock(&pipeMutex);

}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_ReapDetachedProcs --
 *
 *      This function checks to see if any detached processes have exited and,
 *      if so, it "reaps" them by officially waiting on them. It should be
 *      called "occasionally" to make sure that all detached processes are
 *      eventually reaped.
 *
 * Results:
 *      None.
 *
 * Side effects:
 *      Processes are waited on, so that they can be reaped by the system.
 *
 *----------------------------------------------------------------------
 */

void
Tcl_ReapDetachedProcs(void)
{
    register Detached *detPtr;
    Detached *nextPtr, *prevPtr;
    int status;
    Tcl_Pid pid;

    Tcl_MutexLock(&pipeMutex);
    for (detPtr = detList, prevPtr = NULL; detPtr != NULL; ) {
        pid = Tcl_WaitPid(detPtr->pid, &status, WNOHANG);
        if ((pid == 0) || ((pid == (Tcl_Pid) -1) && (errno != ECHILD))) {
            prevPtr = detPtr;
            detPtr = detPtr->nextPtr;
            continue;
        }
        nextPtr = detPtr->nextPtr;
        if (prevPtr == NULL) {
            detList = detPtr->nextPtr;
        } else {
            prevPtr->nextPtr = detPtr->nextPtr;
        }
        ckfree((char *) detPtr);
        detPtr = nextPtr;
    }
    Tcl_MutexUnlock(&pipeMutex);
}

/*
 *----------------------------------------------------------------------
 *
 * TclCleanupChildren --
 *
 *      This is a utility function used to wait for child processes to exit,
 *      record information about abnormal exits, and then collect any stderr
 *      output generated by them.
 *
 * Results:
 *      The return value is a standard Tcl result. If anything at weird
 *      happened with the child processes, TCL_ERROR is returned and a message
 *      is left in the interp's result.
 *
 * Side effects:
 *      If the last character of the interp's result is a newline, then it is
 *      removed unless keepNewline is non-zero. File errorId gets closed, and
 *      pidPtr is freed back to the storage allocator.
 *
 *----------------------------------------------------------------------
 */

int
TclCleanupChildren(
    Tcl_Interp *interp,         /* Used for error messages. */
    int numPids,                /* Number of entries in pidPtr array. */
    Tcl_Pid *pidPtr,            /* Array of process ids of children. */
    Tcl_Channel errorChan)      /* Channel for file containing stderr output
                                 * from pipeline. NULL means there isn't any
                                 * stderr output. */
{
    int result = TCL_OK;
    int i, abnormalExit, anyErrorInfo;
    Tcl_Pid pid;
    WAIT_STATUS_TYPE waitStatus;
    CONST char *msg;
    unsigned long resolvedPid;

    abnormalExit = 0;
    for (i = 0; i < numPids; i++) {
        /*
         * We need to get the resolved pid before we wait on it as the windows
         * implimentation of Tcl_WaitPid deletes the information such that any
         * following calls to TclpGetPid fail.
         */

        resolvedPid = TclpGetPid(pidPtr[i]);
        pid = Tcl_WaitPid(pidPtr[i], (int *) &waitStatus, 0);
        if (pid == (Tcl_Pid) -1) {
            result = TCL_ERROR;
            if (interp != NULL) {
                msg = Tcl_PosixError(interp);
                if (errno == ECHILD) {
                    /*
                     * This changeup in message suggested by Mark Diekhans to
                     * remind people that ECHILD errors can occur on some
                     * systems if SIGCHLD isn't in its default state.
                     */

                    msg =
                        "child process lost (is SIGCHLD ignored or trapped?)";
                }
                Tcl_AppendResult(interp, "error waiting for process to exit: ",
                        msg, NULL);
            }
            continue;
        }

        /*
         * Create error messages for unusual process exits. An extra newline
         * gets appended to each error message, but it gets removed below (in
         * the same fashion that an extra newline in the command's output is
         * removed).
         */

        if (!WIFEXITED(waitStatus) || (WEXITSTATUS(waitStatus) != 0)) {
            char msg1[TCL_INTEGER_SPACE], msg2[TCL_INTEGER_SPACE];

            result = TCL_ERROR;
            sprintf(msg1, "%lu", resolvedPid);
            if (WIFEXITED(waitStatus)) {
                if (interp != (Tcl_Interp *) NULL) {
                    sprintf(msg2, "%lu",
                            (unsigned long) WEXITSTATUS(waitStatus));
                    Tcl_SetErrorCode(interp, "CHILDSTATUS", msg1, msg2, NULL);
                }
                abnormalExit = 1;
            } else if (interp != NULL) {
                CONST char *p;

                if (WIFSIGNALED(waitStatus)) {
                    p = Tcl_SignalMsg((int) (WTERMSIG(waitStatus)));
                    Tcl_SetErrorCode(interp, "CHILDKILLED", msg1,
                            Tcl_SignalId((int) (WTERMSIG(waitStatus))), p,
                            NULL);
                    Tcl_AppendResult(interp, "child killed: ", p, "\n", NULL);
                } else if (WIFSTOPPED(waitStatus)) {
                    p = Tcl_SignalMsg((int) (WSTOPSIG(waitStatus)));
                    Tcl_SetErrorCode(interp, "CHILDSUSP", msg1,
                            Tcl_SignalId((int) (WSTOPSIG(waitStatus))), p,
                            NULL);
                    Tcl_AppendResult(interp, "child suspended: ", p, "\n",
                            NULL);
                } else {
                    Tcl_AppendResult(interp,
                            "child wait status didn't make sense\n", NULL);
                }
            }
        }
    }

    /*
     * Read the standard error file. If there's anything there, then return an
     * error and add the file's contents to the result string.
     */

    anyErrorInfo = 0;
    if (errorChan != NULL) {
        /*
         * Make sure we start at the beginning of the file.
         */

        if (interp != NULL) {
            int count;
            Tcl_Obj *objPtr;

            Tcl_Seek(errorChan, (Tcl_WideInt)0, SEEK_SET);
            objPtr = Tcl_NewObj();
            count = Tcl_ReadChars(errorChan, objPtr, -1, 0);
            if (count < 0) {
                result = TCL_ERROR;
                Tcl_DecrRefCount(objPtr);
                Tcl_ResetResult(interp);
                Tcl_AppendResult(interp, "error reading stderr output file: ",
                        Tcl_PosixError(interp), NULL);
            } else if (count > 0) {
                anyErrorInfo = 1;
                Tcl_SetObjResult(interp, objPtr);
                result = TCL_ERROR;
            } else {
                Tcl_DecrRefCount(objPtr);
            }
        }
        Tcl_Close(NULL, errorChan);
    }

    /*
     * If a child exited abnormally but didn't output any error information at
     * all, generate an error message here.
     */

    if ((abnormalExit != 0) && (anyErrorInfo == 0) && (interp != NULL)) {
        Tcl_AppendResult(interp, "child process exited abnormally", NULL);
    }
    return result;
}

/*
 *----------------------------------------------------------------------
 *
 * TclCreatePipeline --
 *
 *      Given an argc/argv array, instantiate a pipeline of processes as
 *      described by the argv.
 *
 *      This function is unofficially exported for use by BLT.
 *
 * Results:
 *      The return value is a count of the number of new processes created, or
 *      -1 if an error occurred while creating the pipeline. *pidArrayPtr is
 *      filled in with the address of a dynamically allocated array giving the
 *      ids of all of the processes. It is up to the caller to free this array
 *      when it isn't needed anymore. If inPipePtr is non-NULL, *inPipePtr is
 *      filled in with the file id for the input pipe for the pipeline (if
 *      any): the caller must eventually close this file. If outPipePtr isn't
 *      NULL, then *outPipePtr is filled in with the file id for the output
 *      pipe from the pipeline: the caller must close this file. If errFilePtr
 *      isn't NULL, then *errFilePtr is filled with a file id that may be used
 *      to read error output after the pipeline completes.
 *
 * Side effects:
 *      Processes and pipes are created.
 *
 *----------------------------------------------------------------------
 */

int
TclCreatePipeline(
    Tcl_Interp *interp,         /* Interpreter to use for error reporting. */
    int argc,                   /* Number of entries in argv. */
    CONST char **argv,          /* Array of strings describing commands in
                                 * pipeline plus I/O redirection with <, <<,
                                 * >, etc. Argv[argc] must be NULL. */
    Tcl_Pid **pidArrayPtr,      /* Word at *pidArrayPtr gets filled in with
                                 * address of array of pids for processes in
                                 * pipeline (first pid is first process in
                                 * pipeline). */
    TclFile *inPipePtr,         /* If non-NULL, input to the pipeline comes
                                 * from a pipe (unless overridden by
                                 * redirection in the command). The file id
                                 * with which to write to this pipe is stored
                                 * at *inPipePtr. NULL means command specified
                                 * its own input source. */
    TclFile *outPipePtr,        /* If non-NULL, output to the pipeline goes to
                                 * a pipe, unless overriden by redirection in
                                 * the command. The file id with which to read
                                 * frome this pipe is stored at *outPipePtr.
                                 * NULL means command specified its own output
                                 * sink. */
    TclFile *errFilePtr)        /* If non-NULL, all stderr output from the
                                 * pipeline will go to a temporary file
                                 * created here, and a descriptor to read the
                                 * file will be left at *errFilePtr. The file
                                 * will be removed already, so closing this
                                 * descriptor will be the end of the file. If
                                 * this is NULL, then all stderr output goes
                                 * to our stderr. If the pipeline specifies
                                 * redirection then the file will still be
                                 * created but it will never get any data. */
{
    Tcl_Pid *pidPtr = NULL;     /* Points to malloc-ed array holding all the
                                 * pids of child processes. */
    int numPids;                /* Actual number of processes that exist at
                                 * *pidPtr right now. */
    int cmdCount;               /* Count of number of distinct commands found
                                 * in argc/argv. */
    CONST char *inputLiteral = NULL;
                                /* If non-null, then this points to a string
                                 * containing input data (specified via <<) to
                                 * be piped to the first process in the
                                 * pipeline. */
    TclFile inputFile = NULL;   /* If != NULL, gives file to use as input for
                                 * first process in pipeline (specified via <
                                 * or <@). */
    int inputClose = 0;         /* If non-zero, then inputFile should be
                                 * closed when cleaning up. */
    int inputRelease = 0;
    TclFile outputFile = NULL;  /* Writable file for output from last command
                                 * in pipeline (could be file or pipe). NULL
                                 * means use stdout. */
    int outputClose = 0;        /* If non-zero, then outputFile should be
                                 * closed when cleaning up. */
    int outputRelease = 0;
    TclFile errorFile = NULL;   /* Writable file for error output from all
                                 * commands in pipeline. NULL means use
                                 * stderr. */
    int errorClose = 0;         /* If non-zero, then errorFile should be
                                 * closed when cleaning up. */
    int errorRelease = 0;
    CONST char *p;
    CONST char *nextArg;
    int skip, lastBar, lastArg, i, j, atOK, flags, needCmd, errorToOutput = 0;
    Tcl_DString execBuffer;
    TclFile pipeIn;
    TclFile curInFile, curOutFile, curErrFile;
    Tcl_Channel channel;

    if (inPipePtr != NULL) {
        *inPipePtr = NULL;
    }
    if (outPipePtr != NULL) {
        *outPipePtr = NULL;
    }
    if (errFilePtr != NULL) {
        *errFilePtr = NULL;
    }

    Tcl_DStringInit(&execBuffer);

    pipeIn = NULL;
    curInFile = NULL;
    curOutFile = NULL;
    numPids = 0;

    /*
     * First, scan through all the arguments to figure out the structure of
     * the pipeline. Process all of the input and output redirection arguments
     * and remove them from the argument list in the pipeline. Count the
     * number of distinct processes (it's the number of "|" arguments plus
     * one) but don't remove the "|" arguments because they'll be used in the
     * second pass to seperate the individual child processes. Cannot start
     * the child processes in this pass because the redirection symbols may
     * appear anywhere in the command line - e.g., the '<' that specifies the
     * input to the entire pipe may appear at the very end of the argument
     * list.
     */

    lastBar = -1;
    cmdCount = 1;
    needCmd = 1;
    for (i = 0; i < argc; i++) {
        errorToOutput = 0;
        skip = 0;
        p = argv[i];
        switch (*p++) {
        case '|':
            if (*p == '&') {
                p++;
            }
            if (*p == '\0') {
                if ((i == (lastBar + 1)) || (i == (argc - 1))) {
                    Tcl_SetResult(interp, "illegal use of | or |& in command",
                            TCL_STATIC);
                    goto error;
                }
            }
            lastBar = i;
            cmdCount++;
            needCmd = 1;
            break;

        case '<':
            if (inputClose != 0) {
                inputClose = 0;
                TclpCloseFile(inputFile);
            }
            if (inputRelease != 0) {
                inputRelease = 0;
                TclpReleaseFile(inputFile);
            }
            if (*p == '<') {
                inputFile = NULL;
                inputLiteral = p + 1;
                skip = 1;
                if (*inputLiteral == '\0') {
                    inputLiteral = ((i + 1) == argc) ? NULL : argv[i + 1];
                    if (inputLiteral == NULL) {
                        Tcl_AppendResult(interp, "can't specify \"", argv[i],
                                "\" as last word in command", NULL);
                        goto error;
                    }
                    skip = 2;
                }
            } else {
                nextArg = ((i + 1) == argc) ? NULL : argv[i + 1];
                inputLiteral = NULL;
                inputFile = FileForRedirect(interp, p, 1, argv[i], nextArg,
                        O_RDONLY, &skip, &inputClose, &inputRelease);
                if (inputFile == NULL) {
                    goto error;
                }
            }
            break;

        case '>':
            atOK = 1;
            flags = O_WRONLY | O_CREAT | O_TRUNC;
            if (*p == '>') {
                p++;
                atOK = 0;

                /*
                 * Note that the O_APPEND flag only has an effect on POSIX
                 * platforms. On Windows, we just have to carry on regardless.
                 */

                flags = O_WRONLY | O_CREAT | O_APPEND;
            }
            if (*p == '&') {
                if (errorClose != 0) {
                    errorClose = 0;
                    TclpCloseFile(errorFile);
                }
                errorToOutput = 1;
                p++;
            }

            /*
             * Close the old output file, but only if the error file is not
             * also using it.
             */

            if (outputClose != 0) {
                outputClose = 0;
                if (errorFile == outputFile) {
                    errorClose = 1;
                } else {
                    TclpCloseFile(outputFile);
                }
            }
            if (outputRelease != 0) {
                outputRelease = 0;
                if (errorFile == outputFile) {
                    errorRelease = 1;
                } else {
                    TclpReleaseFile(outputFile);
                }
            }
            nextArg = ((i + 1) == argc) ? NULL : argv[i + 1];
            outputFile = FileForRedirect(interp, p, atOK, argv[i], nextArg,
                    flags, &skip, &outputClose, &outputRelease);
            if (outputFile == NULL) {
                goto error;
            }
            if (errorToOutput) {
                if (errorClose != 0) {
                    errorClose = 0;
                    TclpCloseFile(errorFile);
                }
                if (errorRelease != 0) {
                    errorRelease = 0;
                    TclpReleaseFile(errorFile);
                }
                errorFile = outputFile;
            }
            break;

        case '2':
            if (*p != '>') {
                break;
            }
            p++;
            atOK = 1;
            flags = O_WRONLY | O_CREAT | O_TRUNC;
            if (*p == '>') {
                p++;
                atOK = 0;
                flags = O_WRONLY | O_CREAT;
            }
            if (errorClose != 0) {
                errorClose = 0;
                TclpCloseFile(errorFile);
            }
            if (errorRelease != 0) {
                errorRelease = 0;
                TclpReleaseFile(errorFile);
            }
            if (atOK && p[0] == '@' && p[1] == '1' && p[2] == '\0') {
                /*
                 * Special case handling of 2>@1 to redirect stderr to the
                 * exec/open output pipe as well. This is meant for the end of
                 * the command string, otherwise use |& between commands.
                 */

                if (i != argc-1) {
                    Tcl_AppendResult(interp, "must specify \"", argv[i],
                            "\" as last word in command", NULL);
                    goto error;
                }
                errorFile = outputFile;
                errorToOutput = 2;
                skip = 1;
            } else {
                nextArg = ((i + 1) == argc) ? NULL : argv[i + 1];
                errorFile = FileForRedirect(interp, p, atOK, argv[i],
                        nextArg, flags, &skip, &errorClose, &errorRelease);
                if (errorFile == NULL) {
                    goto error;
                }
            }
            break;

        default:
          /* Got a command word, not a redirection */
          needCmd = 0;
          break;
        }

        if (skip != 0) {
            for (j = i + skip; j < argc; j++) {
                argv[j - skip] = argv[j];
            }
            argc -= skip;
            i -= 1;
        }
    }

    if (needCmd) {
        /* We had a bar followed only by redirections. */

        Tcl_SetResult(interp,
                      "illegal use of | or |& in command",
                      TCL_STATIC);
        goto error;
    }

    if (inputFile == NULL) {
        if (inputLiteral != NULL) {
            /*
             * The input for the first process is immediate data coming from
             * Tcl. Create a temporary file for it and put the data into the
             * file.
             */

            inputFile = TclpCreateTempFile(inputLiteral);
            if (inputFile == NULL) {
                Tcl_AppendResult(interp,
                        "couldn't create input file for command: ",
                        Tcl_PosixError(interp), NULL);
                goto error;
            }
            inputClose = 1;
        } else if (inPipePtr != NULL) {
            /*
             * The input for the first process in the pipeline is to come from
             * a pipe that can be written from by the caller.
             */

            if (TclpCreatePipe(&inputFile, inPipePtr) == 0) {
                Tcl_AppendResult(interp,
                        "couldn't create input pipe for command: ",
                        Tcl_PosixError(interp), NULL);
                goto error;
            }
            inputClose = 1;
        } else {
            /*
             * The input for the first process comes from stdin.
             */

            channel = Tcl_GetStdChannel(TCL_STDIN);
            if (channel != NULL) {
                inputFile = TclpMakeFile(channel, TCL_READABLE);
                if (inputFile != NULL) {
                    inputRelease = 1;
                }
            }
        }
    }

    if (outputFile == NULL) {
        if (outPipePtr != NULL) {
            /*
             * Output from the last process in the pipeline is to go to a pipe
             * that can be read by the caller.
             */

            if (TclpCreatePipe(outPipePtr, &outputFile) == 0) {
                Tcl_AppendResult(interp,
                        "couldn't create output pipe for command: ",
                        Tcl_PosixError(interp), NULL);
                goto error;
            }
            outputClose = 1;
        } else {
            /*
             * The output for the last process goes to stdout.
             */

            channel = Tcl_GetStdChannel(TCL_STDOUT);
            if (channel) {
                outputFile = TclpMakeFile(channel, TCL_WRITABLE);
                if (outputFile != NULL) {
                    outputRelease = 1;
                }
            }
        }
    }

    if (errorFile == NULL) {
        if (errorToOutput == 2) {
            /*
             * Handle 2>@1 special case at end of cmd line.
             */

            errorFile = outputFile;
        } else if (errFilePtr != NULL) {
            /*
             * Set up the standard error output sink for the pipeline, if
             * requested. Use a temporary file which is opened, then deleted.
             * Could potentially just use pipe, but if it filled up it could
             * cause the pipeline to deadlock: we'd be waiting for processes
             * to complete before reading stderr, and processes couldn't
             * complete because stderr was backed up.
             */

            errorFile = TclpCreateTempFile(NULL);
            if (errorFile == NULL) {
                Tcl_AppendResult(interp,
                        "couldn't create error file for command: ",
                        Tcl_PosixError(interp), NULL);
                goto error;
            }
            *errFilePtr = errorFile;
        } else {
            /*
             * Errors from the pipeline go to stderr.
             */

            channel = Tcl_GetStdChannel(TCL_STDERR);
            if (channel) {
                errorFile = TclpMakeFile(channel, TCL_WRITABLE);
                if (errorFile != NULL) {
                    errorRelease = 1;
                }
            }
        }
    }

    /*
     * Scan through the argc array, creating a process for each group of
     * arguments between the "|" characters.
     */

    Tcl_ReapDetachedProcs();
    pidPtr = (Tcl_Pid *) ckalloc((unsigned) (cmdCount * sizeof(Tcl_Pid)));

    curInFile = inputFile;

    for (i = 0; i < argc; i = lastArg + 1) {
        int result, joinThisError;
        Tcl_Pid pid;
        CONST char *oldName;

        /*
         * Convert the program name into native form.
         */

        if (Tcl_TranslateFileName(interp, argv[i], &execBuffer) == NULL) {
            goto error;
        }

        /*
         * Find the end of the current segment of the pipeline.
         */

        joinThisError = 0;
        for (lastArg = i; lastArg < argc; lastArg++) {
            if (argv[lastArg][0] != '|') {
                continue;
            }
            if (argv[lastArg][1] == '\0') {
                break;
            }
            if ((argv[lastArg][1] == '&') && (argv[lastArg][2] == '\0')) {
                joinThisError = 1;
                break;
            }
        }

        /*
         * If this is the last segment, use the specified outputFile.
         * Otherwise create an intermediate pipe. pipeIn will become the
         * curInFile for the next segment of the pipe.
         */

        if (lastArg == argc) {
            curOutFile = outputFile;
        } else {
            argv[lastArg] = NULL;
            if (TclpCreatePipe(&pipeIn, &curOutFile) == 0) {
                Tcl_AppendResult(interp, "couldn't create pipe: ",
                        Tcl_PosixError(interp), NULL);
                goto error;
            }
        }

        if (joinThisError != 0) {
            curErrFile = curOutFile;
        } else {
            curErrFile = errorFile;
        }

        /*
         * Restore argv[i], since a caller wouldn't expect the contents of
         * argv to be modified.
         */

        oldName = argv[i];
        argv[i] = Tcl_DStringValue(&execBuffer);
        result = TclpCreateProcess(interp, lastArg - i, argv + i,
                curInFile, curOutFile, curErrFile, &pid);
        argv[i] = oldName;
        if (result != TCL_OK) {
            goto error;
        }
        Tcl_DStringFree(&execBuffer);

        pidPtr[numPids] = pid;
        numPids++;

        /*
         * Close off our copies of file descriptors that were set up for this
         * child, then set up the input for the next child.
         */

        if ((curInFile != NULL) && (curInFile != inputFile)) {
            TclpCloseFile(curInFile);
        }
        curInFile = pipeIn;
        pipeIn = NULL;

        if ((curOutFile != NULL) && (curOutFile != outputFile)) {
            TclpCloseFile(curOutFile);
        }
        curOutFile = NULL;
    }

    *pidArrayPtr = pidPtr;

    /*
     * All done. Cleanup open files lying around and then return.
     */

  cleanup:
    Tcl_DStringFree(&execBuffer);

    if (inputClose) {
        TclpCloseFile(inputFile);
    } else if (inputRelease) {
        TclpReleaseFile(inputFile);
    }
    if (outputClose) {
        TclpCloseFile(outputFile);
    } else if (outputRelease) {
        TclpReleaseFile(outputFile);
    }
    if (errorClose) {
        TclpCloseFile(errorFile);
    } else if (errorRelease) {
        TclpReleaseFile(errorFile);
    }
    return numPids;

    /*
     * An error occurred. There could have been extra files open, such as
     * pipes between children. Clean them all up. Detach any child processes
     * that have been created.
     */

  error:
    if (pipeIn != NULL) {
        TclpCloseFile(pipeIn);
    }
    if ((curOutFile != NULL) && (curOutFile != outputFile)) {
        TclpCloseFile(curOutFile);
    }
    if ((curInFile != NULL) && (curInFile != inputFile)) {
        TclpCloseFile(curInFile);
    }
    if ((inPipePtr != NULL) && (*inPipePtr != NULL)) {
        TclpCloseFile(*inPipePtr);
        *inPipePtr = NULL;
    }
    if ((outPipePtr != NULL) && (*outPipePtr != NULL)) {
        TclpCloseFile(*outPipePtr);
        *outPipePtr = NULL;
    }
    if ((errFilePtr != NULL) && (*errFilePtr != NULL)) {
        TclpCloseFile(*errFilePtr);
        *errFilePtr = NULL;
    }
    if (pidPtr != NULL) {
        for (i = 0; i < numPids; i++) {
            if (pidPtr[i] != (Tcl_Pid) -1) {
                Tcl_DetachPids(1, &pidPtr[i]);
            }
        }
        ckfree((char *) pidPtr);
    }
    numPids = -1;
    goto cleanup;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_OpenCommandChannel --
 *
 *      Opens an I/O channel to one or more subprocesses specified by argc and
 *      argv. The flags argument determines the disposition of the stdio
 *      handles. If the TCL_STDIN flag is set then the standard input for the
 *      first subprocess will be tied to the channel: writing to the channel
 *      will provide input to the subprocess. If TCL_STDIN is not set, then
 *      standard input for the first subprocess will be the same as this
 *      application's standard input. If TCL_STDOUT is set then standard
 *      output from the last subprocess can be read from the channel;
 *      otherwise it goes to this application's standard output. If TCL_STDERR
 *      is set, standard error output for all subprocesses is returned to the
 *      channel and results in an error when the channel is closed; otherwise
 *      it goes to this application's standard error. If TCL_ENFORCE_MODE is
 *      not set, then argc and argv can redirect the stdio handles to override
 *      TCL_STDIN, TCL_STDOUT, and TCL_STDERR; if it is set, then it is an
 *      error for argc and argv to override stdio channels for which
 *      TCL_STDIN, TCL_STDOUT, and TCL_STDERR have been set.
 *
 * Results:
 *      A new command channel, or NULL on failure with an error message left
 *      in interp.
 *
 * Side effects:
 *      Creates processes, opens pipes.
 *
 *----------------------------------------------------------------------
 */

Tcl_Channel
Tcl_OpenCommandChannel(
    Tcl_Interp *interp,         /* Interpreter for error reporting. Can NOT be
                                 * NULL. */
    int argc,                   /* How many arguments. */
    CONST char **argv,          /* Array of arguments for command pipe. */
    int flags)                  /* Or'ed combination of TCL_STDIN, TCL_STDOUT,
                                 * TCL_STDERR, and TCL_ENFORCE_MODE. */
{
    TclFile *inPipePtr, *outPipePtr, *errFilePtr;
    TclFile inPipe, outPipe, errFile;
    int numPids;
    Tcl_Pid *pidPtr;
    Tcl_Channel channel;

    inPipe = outPipe = errFile = NULL;

    inPipePtr = (flags & TCL_STDIN) ? &inPipe : NULL;
    outPipePtr = (flags & TCL_STDOUT) ? &outPipe : NULL;
    errFilePtr = (flags & TCL_STDERR) ? &errFile : NULL;

    numPids = TclCreatePipeline(interp, argc, argv, &pidPtr, inPipePtr,
            outPipePtr, errFilePtr);

    if (numPids < 0) {
        goto error;
    }

    /*
     * Verify that the pipes that were created satisfy the readable/writable
     * constraints.
     */

    if (flags & TCL_ENFORCE_MODE) {
        if ((flags & TCL_STDOUT) && (outPipe == NULL)) {
            Tcl_AppendResult(interp, "can't read output from command:"
                    " standard output was redirected", NULL);
            goto error;
        }
        if ((flags & TCL_STDIN) && (inPipe == NULL)) {
            Tcl_AppendResult(interp, "can't write input to command:"
                    " standard input was redirected", NULL);
            goto error;
        }
    }

    channel = TclpCreateCommandChannel(outPipe, inPipe, errFile,
            numPids, pidPtr);

    if (channel == (Tcl_Channel) NULL) {
        Tcl_AppendResult(interp, "pipe for command could not be created",
                NULL);
        goto error;
    }
    return channel;

  error:
    if (numPids > 0) {
        Tcl_DetachPids(numPids, pidPtr);
        ckfree((char *) pidPtr);
    }
    if (inPipe != NULL) {
        TclpCloseFile(inPipe);
    }
    if (outPipe != NULL) {
        TclpCloseFile(outPipe);
    }
    if (errFile != NULL) {
        TclpCloseFile(errFile);
    }
    return NULL;
}

/*
 * Local Variables:
 * mode: c
 * c-basic-offset: 4
 * fill-column: 78
 * End:
 */