+@c PSPP - a program for statistical analysis.
+@c Copyright (C) 2017, 2020 Free Software Foundation, Inc.
+@c Permission is granted to copy, distribute and/or modify this document
+@c under the terms of the GNU Free Documentation License, Version 1.3
+@c or any later version published by the Free Software Foundation;
+@c with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.
+@c A copy of the license is included in the section entitled "GNU
+@c Free Documentation License".
+@c
@node Combining Data Files
@chapter Combining Data Files
@cmd{ADD FILES}, @cmd{MATCH FILES}, and @cmd{UPDATE} commands. The
following sections describe details specific to each command.
-Each of these commands reads two or more input files and combines
-them. The command's output becomes the new active dataset. The input
-files are not changed on disk.
+Each of these commands reads two or more input files and combines them.
+The command's output becomes the new active dataset.
+None of the commands actually change the input files.
+Therefore, if you want the changes to become permanent, you must explicitly
+save them using an appropriate procedure or transformation (@pxref{System and Portable File IO}).
The syntax of each command begins with a specification of the files to
be read as input. For each input file, specify FILE with a system
subcommands that specify a parenthesized group or groups of variable
names as they appear in the input file, followed by those variables'
new names, separated by an equals sign (@subcmd{=}),
-e.g. @subcmd{/RENAME=(OLD1=NEW1)(OLD2=NEW2)}. To rename a single
+@i{e.g.} @subcmd{/RENAME=(OLD1=NEW1)(OLD2=NEW2)}. To rename a single
variable, the parentheses may be omitted: @subcmd{/RENAME=@var{old}=@var{new}}.
Within a parenthesized group, variables are renamed simultaneously, so
that @subcmd{/RENAME=(@var{A} @var{B}=@var{B} @var{A})} exchanges the
system-missing value for numeric variables or spaces for string
variables.
+These commands may combine any number of files, limited only by the
+machine's memory.
+
@node ADD FILES
@section ADD FILES
@vindex ADD FILES
@end display
@cmd{UPDATE} updates a @dfn{master file} by applying modifications
-from one or more @dfn{transaction files}.
+from one or more @dfn{transaction files}.
@cmd{UPDATE} shares the bulk of its syntax with other @pspp{} commands for
combining multiple data files. @xref{Combining Files Common Syntax},