spawn*

Syntax

#include <process.h> int spawnl(int mode, const char *path, const char *argv0, ..., NULL); int spawnle(int mode, const char *path, const char *argv0, ..., NULL /*, const char **envp */); int spawnlp(int mode, const char *path, const char *argv0, ..., NULL); int spawnlpe(int mode, const char *path, const char *argv0, ..., NULL /*, const char **envp */); int spawnv(int mode, const char *path, char *const argv[]); int spawnve(int mode, const char *path, char *const argv[], char *const envp[]); int spawnvp(int mode, const char *path, char *const argv[]); int spawnvpe(int mode, const char *path, char *const argv[], char *const envp[]);

Description

These functions run other programs. The path points to the program to run, and may optionally include its extension. These functions will look for a file path with the extensions `.com', `.exe', `.bat', and `.btm'; if none are found, neither in the current directory nor along the `PATH', they will look for path itself.

`.com' programs are invoked via the usual DOS calls; DJGPP `.exe' programs are invoked in a way that allows long command lines to be passed; other `.exe' programs are invoked via DOS; `.bat' and `.btm' programs are invoked via the command processor given by the `COMSPEC' environment variable; `.sh', `.ksh' programs and programs with any other extensions that have #! as their first two characters are assumed to be Unix-style scripts and are invoked by calling a program whose pathname immediately follows the first two characters. (If the name of that program is a Unix-style pathname, without a drive letter and without an extension, like `/bin/sh', the spawn functions will additionally look them up on the `PATH'; this allows to run Unix scripts without editing, if you have a shell installed somewhere along your `PATH'.) Any non-recognizable files will be also invoked via DOS calls.

WARNING! DOS is rather stupid in invoking programs: if the file doesn't have the telltale "MZ" signature of the `.exe' style programs, DOS assumes it is a `.com' style image and tries to execute it directly. If the file is not really an executable program, your application will almost certainly crash. Applications that need to be robust in such situations should test whether the program file is indeed an executable, e.g. with calls to stat (see section stat) or _is_executable (see section _is_executable) library functions.

Note that built-in commands of the shells can not be invoked via these functions; use system instead, or invoke the appropriate shell with the built-in command as its argument.

The programs are invoked with the arguments given. The zeroth argument is normally not used, since MS-DOS cannot pass it separately, but for compatibility it should be the name of the program. There are two ways of passing arguments. The l functions (like spawnl) take a list of arguments, with a NULL at the end of the list. This is useful when you know how many argument there will be ahead of time. The v functions (like spawnv) take a pointer to a list of arguments, which also must be NULL-terminated. This is useful when you need to compute the number of arguments at runtime.

In either case, you may also specify e to indicate that you will be giving an explicit environment, else the current environment is used. You may also specify p to indicate that you would like spawn* to search the PATH (in either the environment you pass or the current environment) for the executable, else it will only check the explicit path given.

Note that these function understand about other DJGPP programs, and will call them directly, so that you can pass command lines longer than 126 characters to them without any special code. DJGPP programs called by these functions will not glob the arguments passed to them; other programs also won't glob the arguments if they suppress expansion when given quoted filenames.

When the calling program runs on Windows 9X or Windows 2000 and calls the system shell to run the child program, or if the child program is a native Windows program (in PE-COFF format), or when the system shell is `4DOS' or `NDOS' and the shell is called to run the command, command lines longer than 126 characters are passed via the environment variable CMDLINE.

See section exec*.

Return Value

If successful and mode is P_WAIT, these functions return the exit code of the child process in the lower 8 bits of the return value. Note that if the program is run by a command processor (e.g., if it's a batch file), the exit code of that command processor will be returned. `COMMAND.COM' is notorious for returning 0 even if it couldn't run the command.

If successful and mode is P_OVERLAY, these functions will not return.

If there is an error (e.g., the program specified as argv[0] cannot be run, or the command line is too long), these functions return -1 and set errno to indicate the error. If the child program was interrupted by Ctrl-C or a Critical Device error, errno is set to EINTR (even if the child's exit code is 0), and bits 8-17 of the return value are set to SIGINT or SIGABRT, accordingly. Note that you must set the signal handler for SIGINT to SIG_IGN, or arrange for the handler to return, or else your program will be aborted before it will get chance to set the value of the return code.

Portability

ANSI/ISO C	No
POSIX	No

Example

char *environ[] = { "PATH=c:\\dos;c:\\djgpp;c:\\usr\\local\\bin", "DJGPP=c:/djgpp", 0 }; char *args[] = { "gcc", "-v", "hello.c", 0 }; spawnvpe(P_WAIT, "gcc", args, environ);