File: gprolog050.html

package info (click to toggle)
gprolog 1.3.0-6.1
links: PTS
area: main
in suites: jessie, jessie-kfreebsd, squeeze, wheezy
size: 13,512 kB
ctags: 8,954
sloc: ansic: 57,431; perl: 16,620; sh: 5,900; makefile: 1,284
file content (1648 lines) | stat: -rw-r--r-- 79,652 bytes
parent folder | download | duplicates (2)
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"
            "http://www.w3.org/TR/REC-html40/loose.dtd">
<HTML>
<HEAD>



<META http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<META name="GENERATOR" content="hevea 1.08">
<LINK rel="stylesheet" type="text/css" href="gprolog.css">
<TITLE>
Operating system interface
</TITLE>
</HEAD>
<BODY TEXT=black BGCOLOR=white>
<A HREF="gprolog049.html"><IMG SRC ="previous_motif.gif" ALT="Previous"></A>
<A HREF="gprolog023.html"><IMG SRC ="contents_motif.gif" ALT="Up"></A>
<A HREF="gprolog051.html"><IMG SRC ="next_motif.gif" ALT="Next"></A>
<HR>

<H3 CLASS="subsection"><A NAME="htoc243">7.27</A>&nbsp;&nbsp;Operating system interface</H3><UL>
<LI><A HREF="gprolog050.html#toc195"><TT>argument_counter/1</TT></A>
<LI><A HREF="gprolog050.html#toc196"><TT>argument_value/2</TT></A>
<LI><A HREF="gprolog050.html#toc197"><TT>argument_list/1</TT></A>
<LI><A HREF="gprolog050.html#toc198"><TT>environ/2</TT></A>
<LI><A HREF="gprolog050.html#toc199"><TT>make_directory/1</TT>,
 <TT>delete_directory/1</TT>,
 <TT>change_directory/1</TT></A>
<LI><A HREF="gprolog050.html#toc200"><TT>working_directory/1</TT></A>
<LI><A HREF="gprolog050.html#toc201"><TT>directory_files/2</TT></A>
<LI><A HREF="gprolog050.html#toc202"><TT>rename_file/2</TT></A>
<LI><A HREF="gprolog050.html#toc203"><TT>delete_file/1</TT>,
 <TT>unlink/1</TT></A>
<LI><A HREF="gprolog050.html#toc204"><TT>file_permission/2</TT>,
 <TT>file_exists/1</TT></A>
<LI><A HREF="gprolog050.html#toc205"><TT>file_property/2</TT></A>
<LI><A HREF="gprolog050.html#toc206"><TT>temporary_name/2</TT></A>
<LI><A HREF="gprolog050.html#toc207"><TT>temporary_file/3</TT></A>
<LI><A HREF="gprolog050.html#toc208"><TT>date_time/1</TT></A>
<LI><A HREF="gprolog050.html#toc209"><TT>host_name/1</TT></A>
<LI><A HREF="gprolog050.html#toc210"><TT>os_version/1</TT></A>
<LI><A HREF="gprolog050.html#toc211"><TT>architecture/1</TT></A>
<LI><A HREF="gprolog050.html#toc212"><TT>shell/2</TT>,
 <TT>shell/1</TT>,
 <TT>shell/0</TT></A>
<LI><A HREF="gprolog050.html#toc213"><TT>system/2</TT>,
 <TT>system/1</TT></A>
<LI><A HREF="gprolog050.html#toc214"><TT>spawn/3</TT>,
 <TT>spawn/2</TT></A>
<LI><A HREF="gprolog050.html#toc215"><TT>popen/3</TT></A>
<LI><A HREF="gprolog050.html#toc216"><TT>exec/5</TT>,
 <TT>exec/4</TT></A>
<LI><A HREF="gprolog050.html#toc217"><TT>fork_prolog/1</TT></A>
<LI><A HREF="gprolog050.html#toc218"><TT>create_pipe/2</TT></A>
<LI><A HREF="gprolog050.html#toc219"><TT>wait/2</TT></A>
<LI><A HREF="gprolog050.html#toc220"><TT>prolog_pid/1</TT></A>
<LI><A HREF="gprolog050.html#toc221"><TT>send_signal/2</TT></A>
<LI><A HREF="gprolog050.html#toc222"><TT>sleep/1</TT></A>
<LI><A HREF="gprolog050.html#toc223"><TT>select/5</TT></A>
</UL>

<A NAME="toc195"></A>
<H4 CLASS="subsubsection"><A NAME="htoc244">7.27.1</A>&nbsp;&nbsp;<TT>argument_counter/1</TT></H4>
<A NAME="argument-counter/1"></A>
 
<B>Templates</B>
<DL CLASS="list" COMPACT="compact"><DT CLASS="dt-list"><DD CLASS="dd-list"><TT>
argument_counter(?integer)</TT></DL>
<B>Description</B><BR>
<BR>
<TT>argument_counter(Counter)</TT> succeeds if <TT>Counter</TT> is the
number of arguments of the command-line. Since the first argument is always
the name of the running program, <TT>Counter</TT> is always &#8805; 1. See
(section&nbsp;<A HREF="gprolog006.html#The-GNU-Prolog-interactive-interpreter">3.2</A>) for more information about
command-line arguments retrieved under the top_level.<BR>
<BR>
<B>Errors</B><BR>
<TABLE CELLSPACING=2 CELLPADDING=0>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Counter</TT> is neither a variable nor an integer</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(integer, Counter)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR></TABLE><BR>
<B>Portability</B><BR>
<BR>
GNU Prolog predicate.<BR>
<BR>
<A NAME="toc196"></A>
<H4 CLASS="subsubsection"><A NAME="htoc245">7.27.2</A>&nbsp;&nbsp;<TT>argument_value/2</TT></H4>
<A NAME="argument-value/2"></A>
 
<B>Templates</B>
<DL CLASS="list" COMPACT="compact"><DT CLASS="dt-list"><DD CLASS="dd-list"><TT>
argument_value(+integer, ?atom)</TT></DL>
<B>Description</B><BR>
<BR>
<TT>argument_value(N, Arg)</TT> succeeds if the <TT>N</TT><EM>th</EM>
argument on the command-line unifies with <TT>Arg</TT>. The first argument
is always the name of the running program and its number is 0. The number of
arguments on the command-line can be obtained using
<TT>argument_counter/1</TT> (section&nbsp;<A HREF="#argument-counter/1">7.27.1</A>).<BR>
<BR>
<B>Errors</B><BR>
<TABLE CELLSPACING=2 CELLPADDING=0>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>N</TT> is a variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>N</TT> is neither a variable nor an integer</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(integer, N)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>N</TT> is an integer &lt; 0</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>domain_error(not_less_than_zero, N)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Arg</TT> is neither a variable nor an atom</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(atom, Arg)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR></TABLE><BR>
<B>Portability</B><BR>
<BR>
GNU Prolog predicate.<BR>
<BR>
<A NAME="toc197"></A>
<H4 CLASS="subsubsection"><A NAME="htoc246">7.27.3</A>&nbsp;&nbsp;<TT>argument_list/1</TT></H4>
<A NAME="argument-list/1"></A>
 
<B>Templates</B>
<DL CLASS="list" COMPACT="compact"><DT CLASS="dt-list"><DD CLASS="dd-list"><TT>
argument_list(?list)</TT></DL>
<B>Description</B><BR>
<BR>
<TT>argument_list(Args)</TT> succeeds if <TT>Args</TT> unifies with the
list of atoms associated with each argument on the command-line other than the
first argument (the name of the running program).<BR>
<BR>
<B>Errors</B><BR>
<TABLE CELLSPACING=2 CELLPADDING=0>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Args</TT> is neither a partial list nor a list</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(list, Args)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR></TABLE><BR>
<B>Portability</B><BR>
<BR>
GNU Prolog predicate.<BR>
<BR>
<A NAME="toc198"></A>
<H4 CLASS="subsubsection"><A NAME="htoc247">7.27.4</A>&nbsp;&nbsp;<TT>environ/2</TT></H4>
 
<B>Templates</B>
<DL CLASS="list" COMPACT="compact"><DT CLASS="dt-list"><DD CLASS="dd-list"><TT>
environ(?atom, ?atom)</TT></DL>
<B>Description</B><BR>
<BR>
<TT>environ(Name, Value)</TT> succeeds if <TT>Name</TT> is the name of an
environment variable whose value is <TT>Value</TT>. This predicate is
re-executable on backtracking.<BR>
<BR>
<B>Errors</B><BR>
<TABLE CELLSPACING=2 CELLPADDING=0>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Name</TT> is neither a variable nor an atom</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(atom, Name)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Value</TT> is neither a variable nor an atom</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(atom, Value)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR></TABLE><BR>
<B>Portability</B><BR>
<BR>
GNU Prolog predicate.<BR>
<BR>
<A NAME="toc199"></A>
<H4 CLASS="subsubsection"><A NAME="htoc248">7.27.5</A>&nbsp;&nbsp;<TT>make_directory/1</TT>,
 <TT>delete_directory/1</TT>,
 <TT>change_directory/1</TT></H4>
 
 
 
<B>Templates</B>
<DL CLASS="list" COMPACT="compact"><DT CLASS="dt-list"><DD CLASS="dd-list"><TT>
make_directory(+atom)<BR>
delete_directory(+atom)<BR>
change_directory(+atom)</TT></DL>
<B>Description</B><BR>
<BR>
<TT>make_directory(PathName)</TT> creates the directory whose pathname is
<TT>PathName</TT>. <BR>
<BR>
<TT>delete_directory(PathName)</TT> removes the directory whose pathname is
<TT>PathName</TT>.<BR>
<BR>
<TT>change_directory(PathName)</TT> sets the current directory to the
directory whose pathname is <TT>PathName</TT>.<BR>
<BR>
See <TT>absolute_file_name/2</TT> for information about the syntax of
<TT>PathName</TT> (section&nbsp;<A HREF="gprolog049.html#absolute-file-name/2">7.26.1</A>).<BR>
<BR>
<B>Errors</B><BR>
<TABLE CELLSPACING=2 CELLPADDING=0>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>PathName</TT> is a variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>PathName</TT> is neither a variable nor an atom</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(atom, PathName)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>PathName</TT> is an atom but not a valid pathname</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>domain_error(os_path, PathName)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left>an operating system error occurs and the value of the
<TT>os_error</TT> Prolog flag is <TT>error</TT>
(section&nbsp;<A HREF="gprolog045.html#set-prolog-flag/2">7.22.1</A>)</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>system_error(<I>atom explaining the error</I>)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR></TABLE><BR>
<B>Portability</B><BR>
<BR>
GNU Prolog predicates.<BR>
<BR>
<A NAME="toc200"></A>
<H4 CLASS="subsubsection"><A NAME="htoc249">7.27.6</A>&nbsp;&nbsp;<TT>working_directory/1</TT></H4>
 
<B>Templates</B>
<DL CLASS="list" COMPACT="compact"><DT CLASS="dt-list"><DD CLASS="dd-list"><TT>
working_directory(?atom)</TT></DL>
<B>Description</B><BR>
<BR>
<TT>working_directory(PathName)</TT> succeeds if <TT>PathName</TT> is the
pathname of the current directory. <BR>
<BR>
<B>Errors</B><BR>
<TABLE CELLSPACING=2 CELLPADDING=0>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>PathName</TT> is neither a variable nor an atom</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(atom, PathName)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR></TABLE><BR>
<B>Portability</B><BR>
<BR>
GNU Prolog predicate.<BR>
<BR>
<A NAME="toc201"></A>
<H4 CLASS="subsubsection"><A NAME="htoc250">7.27.7</A>&nbsp;&nbsp;<TT>directory_files/2</TT></H4>
 
<B>Templates</B>
<DL CLASS="list" COMPACT="compact"><DT CLASS="dt-list"><DD CLASS="dd-list"><TT>
directory_files(+atom, ?list)</TT></DL>
<B>Description</B><BR>
<BR>
<TT>directory_files(PathName, Files)</TT> succeeds if <TT>Files</TT> is the
list of all entries (files, sub-directories,...) in the directory whose
pathname is <TT>PathName</TT>. See <TT>absolute_file_name/2</TT> for
information about the syntax of <TT>PathName</TT>
(section&nbsp;<A HREF="gprolog049.html#absolute-file-name/2">7.26.1</A>).<BR>
<BR>
<B>Errors</B><BR>
<TABLE CELLSPACING=2 CELLPADDING=0>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>PathName</TT> is a variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>PathName</TT> is neither a variable nor an atom</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(atom, PathName)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>PathName</TT> is an atom but not a valid pathname</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>domain_error(os_path, PathName)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Files</TT> is neither a partial list nor a list</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(list, Files)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left>an operating system error occurs and the value of the
<TT>os_error</TT> Prolog flag is <TT>error</TT>
(section&nbsp;<A HREF="gprolog045.html#set-prolog-flag/2">7.22.1</A>)</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>system_error(<I>atom explaining the error</I>)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR></TABLE><BR>
<B>Portability</B><BR>
<BR>
GNU Prolog predicate.<BR>
<BR>
<A NAME="toc202"></A>
<H4 CLASS="subsubsection"><A NAME="htoc251">7.27.8</A>&nbsp;&nbsp;<TT>rename_file/2</TT></H4>
 
<B>Templates</B>
<DL CLASS="list" COMPACT="compact"><DT CLASS="dt-list"><DD CLASS="dd-list"><TT>
rename_file(+atom, +atom)</TT></DL>
<B>Description</B><BR>
<BR>
<TT>rename_file(PathName1, PathName2)</TT> renames the file or directory
whose pathname is <TT>PathName1</TT> to <TT>PathName2</TT>. See
<TT>absolute_file_name/2</TT> for information about the syntax of
<TT>PathName1</TT> and <TT>PathName2</TT> (section&nbsp;<A HREF="gprolog049.html#absolute-file-name/2">7.26.1</A>).<BR>
<BR>
<B>Errors</B><BR>
<TABLE CELLSPACING=2 CELLPADDING=0>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>PathName1</TT> is a variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>PathName1</TT> is neither a variable nor an atom</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(atom, PathName1)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>PathName1</TT> is an atom but not a valid pathname</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>domain_error(os_path, PathName1)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>PathName2</TT> is a variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>PathName2</TT> is neither a variable nor an atom</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(atom, PathName2)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>PathName2</TT> is an atom but not a valid pathname</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>domain_error(os_path, PathName2)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left>an operating system error occurs and value of the
<TT>os_error</TT> Prolog flag is <TT>error</TT>
(section&nbsp;<A HREF="gprolog045.html#set-prolog-flag/2">7.22.1</A>)</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>system_error(<I>atom explaining the error</I>)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR></TABLE><BR>
<B>Portability</B><BR>
<BR>
GNU Prolog predicate.<BR>
<BR>
<A NAME="toc203"></A>
<H4 CLASS="subsubsection"><A NAME="htoc252">7.27.9</A>&nbsp;&nbsp;<TT>delete_file/1</TT>,
 <TT>unlink/1</TT></H4>
 
 
<B>Templates</B>
<DL CLASS="list" COMPACT="compact"><DT CLASS="dt-list"><DD CLASS="dd-list"><TT>
delete_file(PathName)<BR>
unlink(PathName)</TT></DL>
<B>Description</B><BR>
<BR>
<TT>delete_file(PathName)</TT> removes the existing file whose pathname is
<TT>PathName</TT>.<BR>
<BR>
<TT>unlink/1</TT> is similar to <TT>delete_file/1</TT> except that it never
causes a <TT>system_error</TT> (e.g. if <TT>PathName</TT> does not refer to
an existing file).<BR>
<BR>
See <TT>absolute_file_name/2</TT> for information about the syntax of
<TT>PathName</TT> (section&nbsp;<A HREF="gprolog049.html#absolute-file-name/2">7.26.1</A>).<BR>
<BR>
<B>Errors</B><BR>
<TABLE CELLSPACING=2 CELLPADDING=0>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>PathName</TT> is a variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>PathName</TT> is neither a variable nor an atom</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(atom, PathName)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>PathName</TT> is an atom but not a valid pathname</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>domain_error(os_path, PathName)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left>an operating system error occurs and the value of the
<TT>os_error</TT> Prolog flag is <TT>error</TT>
(section&nbsp;<A HREF="gprolog045.html#set-prolog-flag/2">7.22.1</A>)</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>system_error(<I>atom explaining the error</I>)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR></TABLE><BR>
<B>Portability</B><BR>
<BR>
GNU Prolog predicates.<BR>
<BR>
<A NAME="toc204"></A>
<H4 CLASS="subsubsection"><A NAME="htoc253">7.27.10</A>&nbsp;&nbsp;<TT>file_permission/2</TT>,
 <TT>file_exists/1</TT></H4>
<A NAME="file-permission/2"></A>
 
 
<B>Templates</B>
<DL CLASS="list" COMPACT="compact"><DT CLASS="dt-list"><DD CLASS="dd-list"><TT>
file_permission(+atom, +atom)<BR>
file_permission(+atom, +atom_list)<BR>
file_exists(+atom)</TT></DL>
<B>Description</B><BR>
<BR>
<TT>file_permission(PathName, Permission)</TT> succeeds if
<TT>PathName</TT> is the pathname of an existing file (or directory) whose
permissions include <TT>Permission</TT>.<BR>
<BR>
<B>File permissions</B>: <TT>Permission</TT> can be a single permission or
a list of permissions. A permission is an atom among: 
<UL CLASS="itemize"><LI CLASS="li-itemize"><TT>read</TT>: the file or directory can be read.<BR>
<BR>
<LI CLASS="li-itemize"><TT>write</TT>: the file or directory can be written.<BR>
<BR>
<LI CLASS="li-itemize"><TT>execute</TT>: the file can be executed.<BR>
<BR>
<LI CLASS="li-itemize"><TT>search</TT>: the directory can be searched.</UL>
If <TT>PathName</TT> does not exists or if it its permissions do not include
<TT>Permission</TT> this predicate fails.<BR>
<BR>
<TT>file_exists(PathName)</TT> is equivalent to
<TT>file_permission(PathName, [])</TT>, i.e. it succeeds if
<TT>PathName</TT> is the pathname of an existing file (or directory).<BR>
<BR>
See <TT>absolute_file_name/2</TT> for information about the syntax of
<TT>PathName</TT> (section&nbsp;<A HREF="gprolog049.html#absolute-file-name/2">7.26.1</A>).<BR>
<BR>
<B>Errors</B><BR>
<TABLE CELLSPACING=2 CELLPADDING=0>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>PathName</TT> is a variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>PathName</TT> is neither a variable nor an atom</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(atom, PathName)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>PathName</TT> is an atom but not a valid pathname</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>domain_error(os_path, PathName)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Permission</TT> is a partial list or a list with an element
which is a variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Permission</TT> is neither an atom nor partial list or a list</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(list, Permission)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left>an element <TT>E</TT> of the <TT>Permission</TT> list is neither a
variable nor an atom</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(atom, E)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left>an element <TT>E</TT> of the <TT>Permission</TT> is an atom but not
a valid permission</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>domain_error(os_file_permission, Permission)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left>an operating system error occurs and the value of the
<TT>os_error</TT> Prolog flag is <TT>error</TT>
(section&nbsp;<A HREF="gprolog045.html#set-prolog-flag/2">7.22.1</A>)</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>system_error(<I>atom explaining the error</I>)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR></TABLE><BR>
<B>Portability</B><BR>
<BR>
GNU Prolog predicates.<BR>
<BR>
<A NAME="toc205"></A>
<H4 CLASS="subsubsection"><A NAME="htoc254">7.27.11</A>&nbsp;&nbsp;<TT>file_property/2</TT></H4>
<A NAME="file-property/2"></A>
 
<B>Templates</B>
<DL CLASS="list" COMPACT="compact"><DT CLASS="dt-list"><DD CLASS="dd-list"><TT>
file_property(+atom, ?os_file_property)</TT></DL>
<B>Description</B><BR>
<BR>
<TT>file_property(PathName, Property)</TT> succeeds if <TT>PathName</TT> is
the pathname of an existing file (or directory) and if <TT>Property</TT>
unifies with one of the properties of the file. This predicate is
re-executable on backtracking.<BR>
<BR>
<B>File properties</B>:
<UL CLASS="itemize"><LI CLASS="li-itemize"><TT>absolute_file_name(File)</TT>:
<TT>File</TT> is the absolute file name of <TT>PathName</TT>
(section&nbsp;<A HREF="gprolog049.html#absolute-file-name/2">7.26.1</A>).<BR>
<BR>
<LI CLASS="li-itemize"><TT>real_file_name(File)</TT>: <TT>File</TT> is
the real file name of <TT>PathName</TT> (follows symbolic links).<BR>
<BR>
<LI CLASS="li-itemize"><TT>type(Type)</TT>: <TT>Type</TT> is the type of
 <TT>PathName</TT>. Possible values are: <TT>regular</TT>,
 <TT>directory</TT>, <TT>fifo</TT>, <TT>socket</TT>, 
<TT>character_device</TT>, <TT>block_device</TT> or <TT>unknown</TT>.<BR>
<BR>
<LI CLASS="li-itemize"><TT>size(Size)</TT>: <TT>Size</TT> is the size (in bytes) of
<TT>PathName</TT>.<BR>
<BR>
<LI CLASS="li-itemize"><TT>permission(Permission)</TT>: <TT>Permission</TT> is a
permission of <TT>PathName</TT> (section&nbsp;<A HREF="#file-permission/2">7.27.10</A>).<BR>
<BR>
<LI CLASS="li-itemize"><TT>last_modification(DT)</TT>: <TT>DT</TT> is
the last modification date and time (section&nbsp;<A HREF="#date-time/1">7.27.14</A>).</UL>
See <TT>absolute_file_name/2</TT> for information about the syntax of
<TT>PathName</TT> (section&nbsp;<A HREF="gprolog049.html#absolute-file-name/2">7.26.1</A>).<BR>
<BR>
<B>Errors</B><BR>
<TABLE CELLSPACING=2 CELLPADDING=0>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>PathName</TT> is a variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>PathName</TT> is neither a variable nor an atom</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(atom, PathName)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>PathName</TT> is an atom but not a valid pathname</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>domain_error(os_path, PathName)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Property</TT> is neither a variable nor a file property term</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>domain_error(os_file_property, Property)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Property</TT> = <TT>absolute_file_name(E)</TT>,
<TT>real_file_name(E)</TT>, <TT>type(E)</TT> or <TT>permission(E)</TT> and
<TT>E</TT> is neither a variable nor an atom</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(atom, E)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Property</TT> = <TT>last_modification(DateTime)</TT> and
<TT>DateTime</TT> is neither a variable nor a compound term</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(compound, DateTime)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Property</TT> = <TT>last_modification(DateTime)</TT> and
<TT>DateTime</TT> is a compound term but not a structure <TT>dt/6</TT></TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>domain_error(date_time, DateTime)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Property</TT> = <TT>size(E)</TT> or
<TT>last_modification(DateTime)</TT> and <TT>DateTime</TT> is a structure
<TT>dt/6</TT> but an element <TT>E</TT> is neither a variable nor an
integer</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(integer, E)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left>an operating system error occurs and the value of the
<TT>os_error</TT> Prolog flag is <TT>error</TT>
(section&nbsp;<A HREF="gprolog045.html#set-prolog-flag/2">7.22.1</A>)</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>system_error(<I>atom explaining the error</I>)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR></TABLE><BR>
<B>Portability</B><BR>
<BR>
GNU Prolog predicate.<BR>
<BR>
<A NAME="toc206"></A>
<H4 CLASS="subsubsection"><A NAME="htoc255">7.27.12</A>&nbsp;&nbsp;<TT>temporary_name/2</TT></H4>
 
<B>Templates</B>
<DL CLASS="list" COMPACT="compact"><DT CLASS="dt-list"><DD CLASS="dd-list"><TT>
temporary_name(+atom, ?atom)</TT></DL>
<B>Description</B><BR>
<BR>
<TT>temporary_name(Template, PathName)</TT> creates a unique file name
<TT>PathName</TT> whose pathname begins by <TT>Template</TT>.
<TT>Template</TT> should contain a pathname with six trailing
<TT>X</TT><EM>s</EM>. <TT>PathName</TT> is <TT>Template</TT> with the six
<TT>X</TT><EM>s</EM> replaced with a letter and the process identifier. This
predicate is an interface to the C Unix function <TT>mktemp(3)</TT>.<BR>
<BR>
See <TT>absolute_file_name/2</TT> for information about the syntax of
<TT>Template</TT> (section&nbsp;<A HREF="gprolog049.html#absolute-file-name/2">7.26.1</A>).<BR>
<BR>
<B>Errors</B><BR>
<TABLE CELLSPACING=2 CELLPADDING=0>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Template</TT> is a variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Template</TT> is neither a variable nor an atom</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(atom, Template)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Template</TT> is an atom but not a valid pathname</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>domain_error(os_path, Template)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>PathName</TT> is neither a variable nor an atom</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(atom, PathName)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left>an operating system error occurs and the value of the
<TT>os_error</TT> Prolog flag is <TT>error</TT>
(section&nbsp;<A HREF="gprolog045.html#set-prolog-flag/2">7.22.1</A>)</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>system_error(<I>atom explaining the error</I>)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR></TABLE><BR>
<B>Portability</B><BR>
<BR>
GNU Prolog predicate.<BR>
<BR>
<A NAME="toc207"></A>
<H4 CLASS="subsubsection"><A NAME="htoc256">7.27.13</A>&nbsp;&nbsp;<TT>temporary_file/3</TT></H4>
 
<B>Templates</B>
<DL CLASS="list" COMPACT="compact"><DT CLASS="dt-list"><DD CLASS="dd-list"><TT>
temporary_file(+atom, +atom, ?atom)</TT></DL>
<B>Description</B><BR>
<BR>
<TT>temporary_file(Directory, Prefix, PathName)</TT> creates a unique file
name <TT>PathName</TT> whose pathname begins by <TT>Directory/Prefix</TT>.
If <TT>Directory</TT> is the empty atom <TT>&#8221;</TT> a standard temporary
directory will be used (e.g. <TT>/tmp</TT>). <TT>Prefix</TT> can be the
empty atom <TT>&#8221;</TT>. This predicate is an interface to the C Unix
function <TT>tempnam(3)</TT>.<BR>
<BR>
See <TT>absolute_file_name/2</TT> for information about the syntax of
<TT>Directory</TT> (section&nbsp;<A HREF="gprolog049.html#absolute-file-name/2">7.26.1</A>).<BR>
<BR>
<B>Errors</B><BR>
<TABLE CELLSPACING=2 CELLPADDING=0>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Directory</TT> is a variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Directory</TT> is neither a variable nor an atom</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(atom, Directory)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Directory</TT> is an atom but not a valid pathname</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>domain_error(os_path, Directory)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Prefix</TT> is a variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Prefix</TT> is neither a variable nor an atom</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(atom, Prefix)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>PathName</TT> is neither a variable nor an atom</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(atom, PathName)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left>an operating system error occurs and the value of the
<TT>os_error</TT> Prolog flag is <TT>error</TT>
(section&nbsp;<A HREF="gprolog045.html#set-prolog-flag/2">7.22.1</A>)</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>system_error(<I>atom explaining the error</I>)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR></TABLE><BR>
<B>Portability</B><BR>
<BR>
GNU Prolog predicate.<BR>
<BR>
<A NAME="toc208"></A>
<H4 CLASS="subsubsection"><A NAME="htoc257">7.27.14</A>&nbsp;&nbsp;<TT>date_time/1</TT></H4>
<A NAME="date-time/1"></A>
 
<B>Templates</B>
<DL CLASS="list" COMPACT="compact"><DT CLASS="dt-list"><DD CLASS="dd-list"><TT>
date_time(?compound)</TT></DL>
<B>Description</B><BR>
<BR>
<TT>date_time(DateTime)</TT> unifies <TT>DateTime</TT> with a compound term
containing the current date and time. <TT>DateTime</TT> is a structure
<TT>dt(Year, Month, Day, Hour, Minute, Second)</TT>. Each sub-argument of
the term <TT>dt/6</TT> is an integer.<BR>
<BR>
<B>Errors</B><BR>
<TABLE CELLSPACING=2 CELLPADDING=0>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>DateTime</TT> is neither a variable nor a compound term</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(compound, DateTime)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>DateTime</TT> is a compound term but not a structure
<TT>dt/6</TT></TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>domain_error(date_time, DateTime)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>DateTime</TT> is a structure <TT>dt/6</TT> and an element
<TT>E</TT> is neither a variable nor an integer</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(integer, E)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR></TABLE><BR>
<B>Portability</B><BR>
<BR>
GNU Prolog predicate.<BR>
<BR>
<A NAME="toc209"></A>
<H4 CLASS="subsubsection"><A NAME="htoc258">7.27.15</A>&nbsp;&nbsp;<TT>host_name/1</TT></H4>
 
<B>Templates</B>
<DL CLASS="list" COMPACT="compact"><DT CLASS="dt-list"><DD CLASS="dd-list"><TT>
host_name(?atom)</TT></DL>
<B>Description</B><BR>
<BR>
<TT>host_name(HostName)</TT> unifies <TT>HostName</TT> with the name of the
host machine executing the current GNU Prolog process. If the sockets are
available (section&nbsp;<A HREF="gprolog051.html#Introduction:(Sockets-input/output)">7.28.1</A>), the name returned
will be fully qualified. In that case, <TT>host_name/1</TT> will also
succeed if <TT>HostName</TT> is instantiated to the unqualified name (or an
alias) of the machine.<BR>
<BR>
<B>Errors</B><BR>
<TABLE CELLSPACING=2 CELLPADDING=0>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Hostname</TT> is neither a variable nor an atom</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(atom, HostName)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left>an operating system error occurs and the value of the
<TT>os_error</TT> Prolog flag is <TT>error</TT>
(section&nbsp;<A HREF="gprolog045.html#set-prolog-flag/2">7.22.1</A>)</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>system_error(<I>atom explaining the error</I>)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR></TABLE><BR>
<B>Portability</B><BR>
<BR>
GNU Prolog predicate.<BR>
<BR>
<A NAME="toc210"></A>
<H4 CLASS="subsubsection"><A NAME="htoc259">7.27.16</A>&nbsp;&nbsp;<TT>os_version/1</TT></H4>
 
<B>Templates</B>
<DL CLASS="list" COMPACT="compact"><DT CLASS="dt-list"><DD CLASS="dd-list"><TT>
os_version(?atom)</TT></DL>
<B>Description</B><BR>
<BR>
<TT>os_version(OSVersion)</TT> unifies <TT>OSVersion</TT> with the
operating system version of the machine executing the current GNU Prolog
process.<BR>
<BR>
<B>Errors</B><BR>
<TABLE CELLSPACING=2 CELLPADDING=0>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>OSVersion</TT> is neither a variable nor an atom</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(atom, OSVersion)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left>an operating system error occurs and the value of the
<TT>os_error</TT> Prolog flag is <TT>error</TT>
(section&nbsp;<A HREF="gprolog045.html#set-prolog-flag/2">7.22.1</A>)</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>system_error(<I>atom explaining the error</I>)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR></TABLE><BR>
<B>Portability</B><BR>
<BR>
GNU Prolog predicate.<BR>
<BR>
<A NAME="toc211"></A>
<H4 CLASS="subsubsection"><A NAME="htoc260">7.27.17</A>&nbsp;&nbsp;<TT>architecture/1</TT></H4>
 
<B>Templates</B>
<DL CLASS="list" COMPACT="compact"><DT CLASS="dt-list"><DD CLASS="dd-list"><TT>
architecture(?atom)</TT></DL>
<B>Description</B><BR>
<BR>
<TT>architecture(Architecture)</TT> unifies <TT>Architecture</TT> with the
name of the machine executing the current GNU Prolog process.<BR>
<BR>
<B>Errors</B><BR>
<TABLE CELLSPACING=2 CELLPADDING=0>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Architecture</TT> is neither a variable nor an atom</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(atom, Architecture)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left>an operating system error occurs and the value of the
<TT>os_error</TT> Prolog flag is <TT>error</TT>
(section&nbsp;<A HREF="gprolog045.html#set-prolog-flag/2">7.22.1</A>)</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>system_error(<I>atom explaining the error</I>)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR></TABLE><BR>
<B>Portability</B><BR>
<BR>
GNU Prolog predicate.<BR>
<BR>
<A NAME="toc212"></A>
<H4 CLASS="subsubsection"><A NAME="htoc261">7.27.18</A>&nbsp;&nbsp;<TT>shell/2</TT>,
 <TT>shell/1</TT>,
 <TT>shell/0</TT></H4>
 
 
 
<B>Templates</B>
<DL CLASS="list" COMPACT="compact"><DT CLASS="dt-list"><DD CLASS="dd-list"><TT>
shell(+atom, ?integer)<BR>
shell(+atom)<BR>
shell</TT></DL>
<B>Description</B><BR>
<BR>
<TT>shell(Command, Status)</TT> invokes a new shell (named by the
<TT>SHELL</TT> environment variable) passing <TT>Command</TT> for execution
and unifies <TT>Status</TT> with the result of the execution. If
<TT>Command</TT> is the empty atom <TT>&#8221;</TT> a new interactive shell is
executed. The control is returned to Prolog upon termination of the called
process.<BR>
<BR>
<TT>shell(Command)</TT> is equivalent to <TT>shell(Command, 0)</TT>.<BR>
<BR>
<TT>shell</TT> is equivalent to <TT>shell(&#8221;, 0)</TT>.<BR>
<BR>
<B>Errors</B><BR>
<TABLE CELLSPACING=2 CELLPADDING=0>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Command</TT> is a variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Command</TT> is neither a variable nor an atom</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(atom, Command)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Status</TT> is neither a variable nor an integer</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(integer, Status)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR></TABLE><BR>
<B>Portability</B><BR>
<BR>
GNU Prolog predicates.<BR>
<BR>
<A NAME="toc213"></A>
<H4 CLASS="subsubsection"><A NAME="htoc262">7.27.19</A>&nbsp;&nbsp;<TT>system/2</TT>,
 <TT>system/1</TT></H4>
 
 
<B>Templates</B>
<DL CLASS="list" COMPACT="compact"><DT CLASS="dt-list"><DD CLASS="dd-list"><TT>
system(+atom, ?integer)<BR>
system(+atom)</TT></DL>
<B>Description</B><BR>
<BR>
<TT>system(Command, Status)</TT> invokes a new default shell passing
<TT>Command</TT> for execution and unifies <TT>Status</TT> with the result
of the execution. The control is returned to Prolog upon termination of the
shell process. This predicate is an interface to the C Unix function
<TT>system(3)</TT>.<BR>
<BR>
<TT>system(Command)</TT> is equivalent to <TT>system(Command, 0)</TT>.<BR>
<BR>
<B>Errors</B><BR>
<TABLE CELLSPACING=2 CELLPADDING=0>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Command</TT> is a variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Command</TT> is neither a variable nor an atom</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(atom, Command)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Status</TT> is neither a variable nor an integer</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(integer, Status)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR></TABLE><BR>
<B>Portability</B><BR>
<BR>
GNU Prolog predicates.<BR>
<BR>
<A NAME="toc214"></A>
<H4 CLASS="subsubsection"><A NAME="htoc263">7.27.20</A>&nbsp;&nbsp;<TT>spawn/3</TT>,
 <TT>spawn/2</TT></H4>
 
 
<B>Templates</B>
<DL CLASS="list" COMPACT="compact"><DT CLASS="dt-list"><DD CLASS="dd-list"><TT>
spawn(+atom, +atom_list, ?integer)<BR>
spawn(+atom, +atom_list)</TT></DL>
<B>Description</B><BR>
<BR>
<TT>spawn(Command, Arguments, Status)</TT> executes <TT>Command</TT> passing
as arguments of the command-line each element of the list <TT>Arguments</TT>
and unifies <TT>Status</TT> with the result of the execution. The control is
returned to Prolog upon termination of the command.<BR>
<BR>
<TT>spawn(Command, Arguments)</TT> is equivalent to <TT>spawn(Command,
Arguments, 0)</TT>.<BR>
<BR>
<B>Errors</B><BR>
<TABLE CELLSPACING=2 CELLPADDING=0>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Command</TT> is a variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Command</TT> is neither a variable nor an atom</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(atom, Command)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Arguments</TT> is a partial list or a list with an element
which is a variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Arguments</TT> is neither a partial list nor a list</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(list, Arguments)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left>an element <TT>E</TT> of the <TT>Arguments</TT> list is neither a
variable nor an atom</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(atom, E)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Status</TT> is neither a variable nor an integer</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(integer, Status)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left>an operating system error occurs and the value of the
<TT>os_error</TT> Prolog flag is <TT>error</TT>
(section&nbsp;<A HREF="gprolog045.html#set-prolog-flag/2">7.22.1</A>)</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>system_error(<I>atom explaining the error</I>)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR></TABLE><BR>
<B>Portability</B><BR>
<BR>
GNU Prolog predicates.<BR>
<BR>
<A NAME="toc215"></A>
<H4 CLASS="subsubsection"><A NAME="htoc264">7.27.21</A>&nbsp;&nbsp;<TT>popen/3</TT></H4>
<A NAME="popen/3"></A>
 
<B>Templates</B>
<DL CLASS="list" COMPACT="compact"><DT CLASS="dt-list"><DD CLASS="dd-list"><TT>
popen(+atom, +io_mode, -stream)</TT></DL>
<B>Description</B><BR>
<BR>
<TT>popen(Command, Mode, Stream)</TT> invokes a new default shell (by
creating a pipe) passing <TT>Command</TT> for execution and associates a
stream either to the standard input or the standard output of the created
process. if <TT>Mode</TT> is <TT>read</TT> (resp. <TT>write</TT>) an input
(resp. output) stream is created and <TT>Stream</TT> is unified with the
stream-term associated. Writing to the stream writes to the standard input
of the command while reading from the stream reads the command's standard
output. The stream must be closed using <TT>close/2</TT> (section&nbsp;<A HREF="gprolog033.html#close/2">7.10.7</A>).
This predicate is an interface to the C Unix function <TT>popen(3)</TT>.<BR>
<BR>
<B>Errors</B><BR>
<TABLE CELLSPACING=2 CELLPADDING=0>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Command</TT> is a variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Command</TT> is neither a variable nor an atom</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(atom, Command)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Mode</TT> is a variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Mode</TT> is neither a variable nor an atom</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(atom, Mode)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Mode</TT> is an atom but neither <TT>read</TT> nor
<TT>write</TT>.</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>domain_error(io_mode, Mode)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Stream</TT> is not a variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(variable, Stream)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left>an operating system error occurs and the value of the
<TT>os_error</TT> Prolog flag is <TT>error</TT>
(section&nbsp;<A HREF="gprolog045.html#set-prolog-flag/2">7.22.1</A>)</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>system_error(<I>atom explaining the error</I>)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR></TABLE><BR>
<B>Portability</B><BR>
<BR>
GNU Prolog predicate.<BR>
<BR>
<A NAME="toc216"></A>
<H4 CLASS="subsubsection"><A NAME="htoc265">7.27.22</A>&nbsp;&nbsp;<TT>exec/5</TT>,
 <TT>exec/4</TT></H4>
 
 
<B>Templates</B>
<DL CLASS="list" COMPACT="compact"><DT CLASS="dt-list"><DD CLASS="dd-list"><TT>
exec(+atom, -stream, -stream, -stream, -integer)<BR>
exec(+atom, -stream, -stream, -stream)</TT></DL>
<B>Description</B><BR>
<BR>
<TT>exec(Command, StreamIn, StreamOut, StreamErr, Pid)</TT> invokes a new
default shell passing <TT>Command</TT> for execution and associates streams
to standard streams of the created process. <TT>StreamIn</TT> is unified
with the stream-term associated with the standard input stream of
<TT>Command</TT> (it is an output stream). <TT>StreamOut</TT> is unified
with the stream-term associated with the standard output stream of
<TT>Command</TT> (it is an input stream). <TT>StreamErr</TT> is unified with
the stream-term associated with the standard error stream of <TT>Command</TT>
(it is an input stream). <TT>Pid</TT> is unified with the process identifier
of the new process. This information is only useful if it is necessary to
obtain the status of the execution using <TT>wait/2</TT> (section&nbsp;<A HREF="#wait/2">7.27.25</A>).
Until a call to <TT>wait/2</TT> is done the process remains in the system
processes table (as a zombie process if terminated). For this reason, if the
status is not needed it is preferable to use <TT>exec/4</TT>.<BR>
<BR>
<TT>exec/4</TT> is similar to <TT>exec/5</TT> but the process is removed
from system processes as soon as it is terminated.<BR>
<BR>
<B>Errors</B><BR>
<TABLE CELLSPACING=2 CELLPADDING=0>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Command</TT> is a variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Command</TT> is neither a variable nor an atom</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(atom, Command)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>StreamIn</TT> is not a variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(variable, StreamIn)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>StreamOut</TT> is not a variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(variable, StreamOut)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>StreamErr</TT> is not a variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(variable, StreamErr)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Pid</TT> is not a variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(variable, Pid)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left>an operating system error occurs and the value of the
<TT>os_error</TT> Prolog flag is <TT>error</TT>
(section&nbsp;<A HREF="gprolog045.html#set-prolog-flag/2">7.22.1</A>)</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>system_error(<I>atom explaining the error</I>)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR></TABLE><BR>
<B>Portability</B><BR>
<BR>
GNU Prolog predicates.<BR>
<BR>
<A NAME="toc217"></A>
<H4 CLASS="subsubsection"><A NAME="htoc266">7.27.23</A>&nbsp;&nbsp;<TT>fork_prolog/1</TT></H4>
 
<B>Templates</B>
<DL CLASS="list" COMPACT="compact"><DT CLASS="dt-list"><DD CLASS="dd-list"><TT>
fork_prolog(-integer)</TT></DL>
<B>Description</B><BR>
<BR>
<TT>fork_prolog(Pid)</TT> creates a child process that differs from the parent
process only in its PID. In the parent process <TT>Pid</TT> is unified with
the PID of the child while in the child process <TT>Pid</TT> is unified with
0. In the parent process, the status of the child process can be ontained
using <TT>wait/2</TT> (section&nbsp;<A HREF="#wait/2">7.27.25</A>). Until a call to <TT>wait/2</TT> is done
the child process remains in the system processes table (as a zombie process
if terminated). This predicate is an interface to the C Unix function
<TT>fork(2)</TT>.<BR>
<BR>
<B>Errors</B><BR>
<TABLE CELLSPACING=2 CELLPADDING=0>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Pid</TT> is not a variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(variable, Pid)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left>an operating system error occurs and the value of the
<TT>os_error</TT> Prolog flag is <TT>error</TT>
(section&nbsp;<A HREF="gprolog045.html#set-prolog-flag/2">7.22.1</A>)</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>system_error(<I>atom explaining the error</I>)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR></TABLE><BR>
<B>Portability</B><BR>
<BR>
GNU Prolog predicate.<BR>
<BR>
<A NAME="toc218"></A>
<H4 CLASS="subsubsection"><A NAME="htoc267">7.27.24</A>&nbsp;&nbsp;<TT>create_pipe/2</TT></H4>
 
<B>Templates</B>
<DL CLASS="list" COMPACT="compact"><DT CLASS="dt-list"><DD CLASS="dd-list"><TT>
create_pipe(-stream, -stream)</TT></DL>
<B>Description</B><BR>
<BR>
<TT>create_pipe(StreamIn, StreamOut)</TT> creates a pair of streams
pointing to a pipe inode. <TT>StreamIn</TT> is unified with the stream-term
associated with the input side of the pipe and <TT>StreamOut</TT> is unified
with the stream-term associated with output side. This predicate is an
interface to the C Unix function <TT>pipe(2)</TT>.<BR>
<BR>
<B>Errors</B><BR>
<TABLE CELLSPACING=2 CELLPADDING=0>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>StreamIn</TT> is not a variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(variable, StreamIn)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>StreamOut</TT> is not a variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(variable, StreamOut)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left>an operating system error occurs and the value of the
<TT>os_error</TT> Prolog flag is <TT>error</TT>
(section&nbsp;<A HREF="gprolog045.html#set-prolog-flag/2">7.22.1</A>)</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>system_error(<I>atom explaining the error</I>)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR></TABLE><BR>
<B>Portability</B><BR>
<BR>
GNU Prolog predicate.<BR>
<BR>
<A NAME="toc219"></A>
<H4 CLASS="subsubsection"><A NAME="htoc268">7.27.25</A>&nbsp;&nbsp;<TT>wait/2</TT></H4>
<A NAME="wait/2"></A>
 
<B>Templates</B>
<DL CLASS="list" COMPACT="compact"><DT CLASS="dt-list"><DD CLASS="dd-list"><TT>
wait(+integer, ?integer)</TT></DL>
<B>Description</B><BR>
<BR>
<TT>wait(Pid, Status)</TT> waits for the child process whose identifier is
<TT>Pid</TT> to terminate. <TT>Status</TT> is then unified with the exit
status. This predicate is an interface to the C Unix function
<TT>waitpid(2)</TT>.<BR>
<BR>
<B>Errors</B><BR>
<TABLE CELLSPACING=2 CELLPADDING=0>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Pid</TT> is a variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Pid</TT> is neither a variable nor an integer</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(integer, Pid)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Status</TT> is neither a variable nor an integer</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(integer, Status)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left>an operating system error occurs and the value of the
<TT>os_error</TT> Prolog flag is <TT>error</TT>
(section&nbsp;<A HREF="gprolog045.html#set-prolog-flag/2">7.22.1</A>)</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>system_error(<I>atom explaining the error</I>)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR></TABLE><BR>
<B>Portability</B><BR>
<BR>
GNU Prolog predicate.<BR>
<BR>
<A NAME="toc220"></A>
<H4 CLASS="subsubsection"><A NAME="htoc269">7.27.26</A>&nbsp;&nbsp;<TT>prolog_pid/1</TT></H4>
 
<B>Templates</B>
<DL CLASS="list" COMPACT="compact"><DT CLASS="dt-list"><DD CLASS="dd-list"><TT>
prolog_pid(?integer)</TT></DL>
<B>Description</B><BR>
<BR>
<TT>prolog_pid(Pid)</TT> unifies <TT>Pid</TT> with the process identifier
of the current GNU Prolog process.<BR>
<BR>
<B>Errors</B><BR>
<TABLE CELLSPACING=2 CELLPADDING=0>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Pid</TT> is neither a variable nor an integer</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(integer, Pid)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR></TABLE><BR>
<B>Portability</B><BR>
<BR>
GNU Prolog predicate.<BR>
<BR>
<A NAME="toc221"></A>
<H4 CLASS="subsubsection"><A NAME="htoc270">7.27.27</A>&nbsp;&nbsp;<TT>send_signal/2</TT></H4>
 
<B>Templates</B>
<DL CLASS="list" COMPACT="compact"><DT CLASS="dt-list"><DD CLASS="dd-list"><TT>
send_signal(+integer, +integer)<BR>
send_signal(+integer, +atom)</TT></DL>
<B>Description</B><BR>
<BR>
<TT>send_signal(Pid, Signal)</TT> sends <TT>Signal</TT> to the process whose
identifier is <TT>Pid.</TT> <TT>Signal</TT> can be specified directly as an
integer or symbolically as an atom. Allowed atoms depend on the machine (e.g.
<TT>'SIGINT'</TT>, <TT>'SIGQUIT'</TT>, <TT>'SIGKILL'</TT>,
<TT>'SIGUSR1'</TT>, <TT>'SIGUSR2'</TT>, <TT>'SIGALRM'</TT>,...). This
predicate is an interface to the C Unix function <TT>kill(2)</TT>.<BR>
<BR>
<B>Errors</B><BR>
<TABLE CELLSPACING=2 CELLPADDING=0>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Pid</TT> is a variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Pid</TT> is neither a variable nor an integer</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(integer, Pid)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Signal</TT> is a variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Signal</TT> is neither a variable nor an integer or an atom</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(integer, Signal)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left>an operating system error occurs and the value of the
<TT>os_error</TT> Prolog flag is <TT>error</TT>
(section&nbsp;<A HREF="gprolog045.html#set-prolog-flag/2">7.22.1</A>)</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>system_error(<I>atom explaining the error</I>)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR></TABLE><BR>
<B>Portability</B><BR>
<BR>
GNU Prolog predicate.<BR>
<BR>
<A NAME="toc222"></A>
<H4 CLASS="subsubsection"><A NAME="htoc271">7.27.28</A>&nbsp;&nbsp;<TT>sleep/1</TT></H4>
 
<B>Templates</B>
<DL CLASS="list" COMPACT="compact"><DT CLASS="dt-list"><DD CLASS="dd-list"><TT>
sleep(+number)</TT></DL>
<B>Description</B><BR>
<BR>
<TT>sleep(Seconds)</TT> puts the GNU Prolog process to sleep for
<TT>Second</TT>s seconds. <TT>Seconds</TT> can be an integer or a floating
point number (in which case it can be &lt; 1). This predicate is an interface
to the C Unix function <TT>usleep(3)</TT>.<BR>
<BR>
<B>Errors</B><BR>
<TABLE CELLSPACING=2 CELLPADDING=0>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Seconds</TT> is a variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Seconds</TT> is neither a variable nor a number</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(number, Seconds)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Seconds</TT> is a number &lt; 0</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>domain_error(not_less_than_zero, Seconds)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR></TABLE><BR>
<B>Portability</B><BR>
<BR>
GNU Prolog predicate.<BR>
<BR>
<A NAME="toc223"></A>
<H4 CLASS="subsubsection"><A NAME="htoc272">7.27.29</A>&nbsp;&nbsp;<TT>select/5</TT></H4>
<A NAME="select/5"></A>
 
<B>Templates</B>
<DL CLASS="list" COMPACT="compact"><DT CLASS="dt-list"><DD CLASS="dd-list"><TT>
select(+list, ?list, +list, ?list, +number)</TT></DL>
<B>Description</B><BR>
<BR>
<TT>select(Reads, ReadyReads, Writes, ReadyWrites, TimeOut)</TT> waits for a
number of streams (or file descriptors) to change status.
<TT>ReadyReads</TT> is unified with the list of elements listed in
<TT>Reads</TT> that have characters available for reading. Similarly
<TT>ReadyWrites</TT> is unified with the list of elements of <TT>Writes</TT>
that are ok for immediate writing. The elements of <TT>Reads</TT> and
<TT>Writes</TT> are either stream-terms or aliases or integers considered as
file descriptors, e.g. for sockets (section&nbsp;<A HREF="gprolog051.html#Sockets-input/output">7.28</A>). Streams
that must be tested with <TT>select/5</TT> should not be buffered. This can
be done at the opening using <TT>open/4</TT> (section&nbsp;<A HREF="gprolog033.html#open/4">7.10.6</A>) or later using
<TT>set_stream_buffering/2</TT> (section&nbsp;<A HREF="gprolog033.html#set-stream-buffering/2">7.10.27</A>).
<TT>TimeOut</TT> is an upper bound on the amount of time (in milliseconds)
elapsed before <TT>select/5</TT> returns. If <TT>TimeOut</TT> &#8804; 0 (no
timeout) <TT>select/5</TT> waits until something is available (either or
reading or for writing) and thus can block indefinitely. This predicate is
an interface to the C Unix function <TT>select(2)</TT>.<BR>
<BR>
<B>Errors</B><BR>
<TABLE CELLSPACING=2 CELLPADDING=0>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Reads</TT> (or <TT>Writes</TT>) is a partial list or a list
with an element <TT>E</TT> which is a variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Reads</TT> is neither a partial list nor a list</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(list, Reads)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Writes</TT> is neither a partial list nor a list</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(list, Writes)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>ReadyReads</TT> is neither a partial list nor a list</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(list, ReadyReads)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>ReadyWrites</TT> is neither a partial list nor a list</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(list, ReadyWrites)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left>an element <TT>E</TT> of the <TT>Reads</TT> (or <TT>Writes</TT>)
list is neither a stream-term or alias nor an integer</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>domain_error(stream_or_alias, E)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left>an element <TT>E</TT> of the <TT>Reads</TT> (or <TT>Writes</TT>)
list is not a selectable item</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>domain_error(selectable_item, E)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left>an element <TT>E</TT> of the <TT>Reads</TT> (or <TT>Writes</TT>)
list is an integer &lt; 0</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>domain_error(not_less_than_zero, E)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left>an element <TT>E</TT> of the <TT>Reads</TT> (or <TT>Writes</TT>)
list is a stream-tern or alias not associated with an open stream</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>existence_error(stream, E)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left>an element <TT>E</TT> of the <TT>Reads</TT> list is associated with
an output stream</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>permission_error(input, stream, E)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left>an element <TT>E</TT> of the <TT>Writes</TT> list is associated with
an input stream</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>permission_error(output, stream, E)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>TimeOut</TT> is a variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>TimeOut</TT> is neither a variable nor a number</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>type_error(number, TimeOut)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left>an operating system error occurs and the value of the
<TT>os_error</TT> Prolog flag is <TT>error</TT>
(section&nbsp;<A HREF="gprolog045.html#set-prolog-flag/2">7.22.1</A>)</TD>
<TD VALIGN=top ALIGN=center NOWRAP>&nbsp;&nbsp;</TD>
<TD VALIGN=top ALIGN=left><TT>system_error(<I>atom explaining the error</I>)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR></TABLE><BR>
<B>Portability</B><BR>
<BR>
GNU Prolog predicate.<BR>
<BR>

<HR SIZE=2>
Copyright (C) 1999-2007 Daniel Diaz
<BR>
<BR>
Verbatim copying and distribution of this entire article is permitted in any
medium, provided this notice is preserved. <BR>
<BR>
<A HREF="index.html#copyright">More about the copyright</A>
<HR>
<A HREF="gprolog049.html"><IMG SRC ="previous_motif.gif" ALT="Previous"></A>
<A HREF="gprolog023.html"><IMG SRC ="contents_motif.gif" ALT="Up"></A>
<A HREF="gprolog051.html"><IMG SRC ="next_motif.gif" ALT="Next"></A>
</BODY>
</HTML>