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<title>exec(3) - Plan 9 from User Space</title>
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<tr><td width=20><td><b>EXEC(3)</b><td align=right><b>EXEC(3)</b>
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<p><font size=+1><b>NAME </b></font><br>
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exec, execl – execute a file<br>
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<p><font size=+1><b>SYNOPSIS </b></font><br>
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<tt><font size=+1>#include <u.h><br>
#include <libc.h>
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<tt><font size=+1>int exec(char *name, char* argv[])<br>
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<tt><font size=+1>int execl(char *name, ...)<br>
</font></tt>
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<p><font size=+1><b>DESCRIPTION </b></font><br>
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<i>Exec</i> and <i>execl</i> overlay the calling process with the named file,
then transfer to the entry point of the image of the file.
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<i>Name</i> points to the name of the file to be executed; it must not
be a directory, and the permissions must allow the current user
to execute it (see <a href="../man3/stat.html"><i>stat</i>(3)</a>). It should also be a valid binary
image, as defined by the local operating system, or a shell script
(see <a href="../man1/rc.html"><i>rc</i>(1)</a>). The first line of a shell script must begin with
<tt><font size=+1>#!</font></tt> followed
by the name of the program to interpret the file and any initial
arguments to that program, for example<br>
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<tt><font size=+1>#!/bin/rc<br>
ls | mc<br>
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</font></tt>
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When a C program is executed, it is called as follows:<br>
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<tt><font size=+1>void main(int argc, char *argv[])<br>
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</font></tt>
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<i>Argv</i> is a copy of the array of argument pointers passed to <i>exec</i>;
that array must end in a null pointer, and <i>argc</i> is the number
of elements before the null pointer. By convention, the first
argument should be the name of the program to be executed. <i>Execl</i>
is like <i>exec</i> except that <i>argv</i> will be an array of the parameters
that follow <i>name</i> in the call. The last argument to <i>execl</i> must
be a null pointer.
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For a file beginning <tt><font size=+1>#!</font></tt>, the arguments passed to the program (<tt><font size=+1>/bin/rc</font></tt>
in the example above) will be the name of the file being executed,
any arguments on the <tt><font size=+1>#!</font></tt> line, the name of the file again, and
finally the second and subsequent arguments given to the original
<i>exec</i> call. The result honors the two conventions
of a program accepting as argument a file to be interpreted and
<tt><font size=+1>argv[0]</font></tt> naming the file being executed.
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Most attributes of the calling process are carried into the result;
in particular, files remain open across <i>exec</i> (except those opened
with <tt><font size=+1>OCEXEC</font></tt> OR’d into the open mode; see <a href="../man3/open.html"><i>open</i>(3)</a>); and the working
directory and environment (see <a href="../man3/getenv.html"><i>getenv</i>(3)</a>) remain the same. However,
a newly <i>exec’ed</i> process has no notification
handlers (see <a href="../man3/notify.html"><i>notify</i>(3)</a>).<br>
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<p><font size=+1><b>SOURCE </b></font><br>
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<tt><font size=+1>/usr/local/plan9/src/lib9/exec.c<br>
/usr/local/plan9/src/lib9/execl.c<br>
</font></tt>
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<p><font size=+1><b>SEE ALSO </b></font><br>
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<a href="../man1/prof.html"><i>prof</i>(1)</a>, <a href="../man3/intro.html"><i>intro</i>(3)</a>, <a href="../man3/stat.html"><i>stat</i>(3)</a><br>
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<p><font size=+1><b>DIAGNOSTICS </b></font><br>
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If these functions fail, they return and set <i>errstr</i>. There can
be no return from a successful <i>exec</i> or <i>execl</i>; the calling image
is lost.<br>
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<p><font size=+1><b>BUGS </b></font><br>
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On Unix, unlike on Plan 9, <i>exec</i> and <i>execl</i> use the user’s current
path to locate <i>prog</i>. This is a clumsy way to deal with Unix’s
lack of a union directory for <tt><font size=+1>/bin</font></tt>.
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To avoid name conflicts with the underlying system, <i>exec</i> and <i>execl</i>
are preprocessor macros defined as <i>p9exec</i> and <i>p9execl</i>; see <a href="../man3/intro.html"><i>intro</i>(3)</a>.<br>
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