How to Shell or Run Another Process with Pascal’s Spawnlp PSS ID Number: Q70008 Article last modified on 03-28-1991 PSS database name: S_PasCal
3.32 4.00
MS-DOS
Summary:
The include file PASEXEC.INC provided with Microsoft Pascal versions 3.32 and 4.00 documents how to spawn to another process (.EXE or .COM) from within a Pascal program. The file PASEXEC.INC can be found on disk 3 for version 4.00 or disk 2 for version 3.32 of Microsoft Pascal.
To spawn (shell or run) to another process requires a call to the external function spawnlp, which is contained within CEXEC.LIB, as shown further below.
Because spawnlp relies on DOS-specific operating system calls, it cannot be used in a program compiled to run under MS OS/2.
This information applies to Microsoft Pascal versions 3.32 and 4.00 for MS-DOS.
More Information:
The function spawnlp is a C function contained within the library CEXEC.LIB. The call (from Pascal) to spawnlp is of the following form:
ReturnCode:=spawnlp(mode,pathname,pathname,arg1, … argn,NULL);
Argument Type Comments ——– —- ——–
ReturnCode Integer Contains a return code if the function call fails. Zero (0) indicates success. mode Integer Can contain the following values: 0 indicates shell _p_overlay is a global variable, which indicates run. pathname ADS pointer Far pointer to a string containing the full path and filename of the process being spawned. arg1…argn ADS pointer A variable number of far pointers indicating the command-line parameters passed to the spawned process. NULL Integer4 Indicates the last argument of the function call. Always has the value of 0.
Below is a program example, PascalSpawn, which first shells to the program Target and then runs to it:
Use the PL compiler as follows to create the files SPAWN.EXE and TARGET.EXE:
PL SPAWN.PAS /link CEXEC.LIB PL TARGET.PAS
SPAWN.PAS
Program PascalSpawn(input,output); const FileName = ‘target.exe’; var _p_overlay [c,extern]:integer; NULL:integer4; i:integer;
function spawnlp : integer [c,varying]; extern; {NOTE: “varying” indicates that a variable number of arguments can be passed to the function}
begin NULL:=0; writeln(‘Shelling to’,Filename); i:=spawnlp(0,ads(FileNamechr(0)), ads(FileNamechr(0)),NULL); if (i = 0) then begin writeln; writeln(‘Successfully returned from the shell!’); writeln; writeln(‘Running to’,Filename); end else begin writeln; writeln(‘Error attempting to shell to’,FileName); end;
i:=spawnlp(_p_overlay,ads(FileNamechr(0)),ads(FileNamechr(0)),NULL); writeln; writeln(‘You should never see this message!’); writeln; writeln(‘Error attempting to run’,FileName); end.
TARGET.PAS
program Target (input,output); begin writeln; writeln(‘In TARGET.EXE’); end.
Copyright Microsoft Corporation 1991.
