gno/usr.man/man3/execl.3

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.\"     from: @(#)exec.3	6.4 (Berkeley) 4/19/91
.\"	exec.3,v 1.2 1993/07/30 08:35:49 mycroft Exp
.\"
.\" This man page has been modified to conform with the lenviron v1.1.3
.\" release for Gno v2.0.3 and later by Devin Reade.  glyn@cs.ualberta.ca
.\"
.TH EXECL 3 "19 January 1997" GNO "Library Routines"
.SH NAME
.BR execl ,
.BR execlp ,
.BR execv ,
.BR execvp
\- execute a file
.SH SYNOPSIS
#include <unistd.h>
.sp 1
extern char **environ;
.sp 1
int
\fBexecl\fR(const char *\fIpath\fR, const char *\fIarg\fR, ...);
.br
int
\fBexecle\fR(const char *\fIpath\fR, const char *\farg\fR, ...);
.br
int
\fBexeclp\fR(const char *\fIfile\fR, const char *\fIarg\fR, ...);
.br
int
\fBexecv\fR(const char *\fIpath\fR, char * const *\fIargv\fR);
.br
int
\fBexecvp\fR(const char *\fIfile\fR, char * const *\fIargv\fR);
.SH DESCRIPTION
The
.BR exec
family of functions replaces the current process image with a
new process image.
The functions described in this manual page are front-ends for the function
\fIexecve\fR(2). (See the manual page for \fIexecve\fR
for detailed information about the replacement of the current process.)
.LP
The initial argument for these functions is the pathname of a file which
is to be executed.
.LP
The
.I arg
and subsequent ellipses in the
.IR execl ,
.IR execle ,
and
.I execlp
functions can be thought of as
.IR arg0 ,
.IR arg1 ,
.IR "..." ,
.IR argn .
Together they describe a list of one or more pointers to NULL-terminated
strings that represent the argument list available to the executed program.
The first argument, by convention, should point to the file name associated
with the file being executed.
The list of arguments
.I must
be terminated by a NULL pointer.
.LP
The
.BR execle
function expects a final argument,
.BR envp ,
of type 'char * const *' to follow
the trailing NULL pointer.  This is an array of environment strings,
similar to that used by
.BR execve (2).
This array
.IR must
be NULL-terminated.
.LP
The
.I execv
and
.I execvp
functions provide an array of pointers to NULL-terminated strings that
represent the argument list available to the new program.
The first argument, by convention, should point to the file name associated
with the file begin executed.
The array of pointers
.I must
be terminated by a NULL pointer.
.LP
Some of these functions have special semantics.
.LP
The functions
.I execlp
and
.I execvp
will duplicate the actions of the shell in searching for an executable file
if the specified file name does not contain a slash (/) character or a
colon (:).
The search path is the path specified in the environment by
.B PATH
variable.
If this variable isn't specified, the default path
.BR "/bin /usr/bin"
(or
.BR "/usr/bin /bin"
for
.BR gsh (1))
is used.
.SH RETURN VALUES
If any of the
.I exec
functions returns, an error will have occurred.
The return value is \fBSYSERR\fR (\-1), and the global variable
.B errno
will be set to indicate the error.
.SH ERRORS
These routines may fail and set
.B errno
for any of the errors specified for the library functions 
.IR execve (2),
.IR _execve (2),
and 
.IR malloc (3).
.SH GNO IMPLEMENTATION
When parsing the
.B PATH
environment variable,
.I execvp
and
.I execlp
assume that if there is no colon (:) within
.B PATH
then the pathname delimiter is a slash (/).  This is to facilitate use
of GS/OS pathname delimiters.
.LP
The current version of the gsh shell searches
.B PATH
from back to front.  In most other shells, it is done front to back.  In
order to provide consistency with gsh,
.B PATH
is currently scanned back to front.  With this backwards scanning, the
default
.B PATH
used is
.BR "/usr/bin /bin" .
If gsh gets fixed, the     
scan order will be quickly changed.
.SH AUTHOR
Implemented from the BSD specification by Devin Reade.
.SH SEE ALSO
.BR execve (2),
.BR fork (2),
.BR exec (3).
.SH HISTORY
The GNO implementation of these routines first appeared in the
.BR lenviron
library.  They became part of the GNO distribution as of v2.0.6