Open System Services System Calls Reference Manual (G06.28+, H06.05+)

execle(2) OSS System Calls Reference Manual

Entering the New Process

When a program is executed as a result of a call to a function in the exec set of functions, it is

entered as a function call as follows:

int main(

int argc,

char ∗∗argv[],

char ∗∗env[]);

Here, the argc parameter is the argument count, the argv[]parameter is an array of character

pointers to the arguments themselves, and env[]is a pointer to a character array listing the

environment variables. The argv[]array is terminated by a null pointer. The null pointer is not

counted in argc.

The arguments speciﬁed by a program with one of the exec set of functions are passed on to the

new process image in the corresponding arguments to the

main() function.

The env[]parameter for the main function is an HP extension and is not the preferred method of

obtaining the environment variables for the new process. Use of the the **environ array of the

new process is the preferred method.

Passing the Arguments and the Environment

Instead of passing the **environ array of the calling process, the environment for the new pro-

cess is provided by following the null pointer that terminates the list of arg parameters with an

additional parameter as if it were declared as:

char ∗∗ const envp[]

The envp[]parameter names an array of character pointers to null-terminated strings. These

strings constitute the environment for the new process image. The environment array is ter-

minated with a null pointer.

The number of bytes available for the new process’s combined argument and environment lists

has a system-imposed limit. This limit, which includes the pointers and the null terminators on

the strings, is available by calling the sysconf(_SC_ARG_MAX) function.

Executing a Binary File

If the ﬁle speciﬁed in the function call is a binary executable ﬁle, the function loads the ﬁle

directly.

Executing a Text File

If the ﬁle speciﬁed in the function call is not a binary executable ﬁle, the function examines the

ﬁle to determine whether it is an executable text ﬁle. The function checks for a header line in the

following format:

#! interpreter_name [optional_string]

The #! notation identiﬁes the ﬁle as an executable text ﬁle. The new process image ﬁlename is

constructed from the process image ﬁlename in the interpreter_name string, treating it like the

path parameter. The arguments passed to the new process are modiﬁed as follows:

• The argv[0] parameter is set to the name of the interpreter.

• If the optional_string portion is present, argv[1] is set to optional_string.

• The next element of argv[]is set to the original value of path.

• The remaining elements of argv[]are set to the original elements of argv[], starting with

the second and subsequent values of the arg parameter.

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