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FUNNELWEB MANUAL WEB PAGE
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Copyright (c) Ross N. Williams 1992,1999. All rights reserved.
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Permission is granted to redistribute and use this manual in
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modifications since the manual's original release by Ross N.
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Williams (www.ross.net) consist of translations or other
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<A HREF="index.html"><FONT COLOR="#FFFFFF"><B>Reference</B></FONT></A><BR>
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<A HREF="intro.html"><FONT COLOR="#FFFFFF">1 Introduction</FONT></A><BR>
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<A HREF="interface.html"><FONT COLOR="#FFFFFF">2 Interface</FONT></A><BR>
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<A HREF="scanner.html"><FONT COLOR="#FFFFFF">3 Scanner</FONT></A><BR>
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<A HREF="parser.html"><FONT COLOR="#FFFFFF">4 Parser</FONT></A><BR>
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<A HREF="analyser.html"><FONT COLOR="#FFFFFF">5 Analyser</FONT></A><BR>
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<A HREF="tangle.html"><FONT COLOR="#FFFFFF">6 Tangle</FONT></A><BR>
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<A HREF="weave.html"><FONT COLOR="#FFFFFF">7 Weave</FONT></A><BR>
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<A HREF="shell.html"><FONT COLOR="#FFFFFF">8 Shell</FONT></A><BR>
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<A HREF="commands.html"><FONT COLOR="#FFFFFF">9 Commands</FONT></A><BR>
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<A HREF="glossary.html"><FONT COLOR="#FFFFFF">10 Glossary</FONT></A><BR>
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<A HREF="references.html"><FONT COLOR="#FFFFFF">11 References</FONT></A><BR>
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<P><FONT SIZE="5">9.6 Diff</FONT><BR>
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<P>The <SAMP>diff</SAMP> command reads in two text files and
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<I>appends</I> a report to a log file containing a list of
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the differences between the two input files. If the log file
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does not already exist, an empty one is created first.
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diff = "diff" s filename s filename s
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diff result.tex answer.tex diff.log
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diff $Otest23.out $Atest23.out $Ldiff.log ABORT
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<P>The <SAMP>diff</SAMP> command performs a full line-based
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differences operation. It will identify different sections
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in a file, even if they are of differing length.
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<P>The implementation of the <SAMP>diff</SAMP> command is
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quite complicated. To be sure that it is at least getting
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its same/different proclamation right, the <SAMP>diff</SAMP>
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command performs a binary comparison as an extra check.
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<P>The following points describe the rules for determining
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<LI> <SAMP>diff</SAMP> aborts with a severe error if the log
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file cannot be opened or created for appending.
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<LI> An ordinary error is generated if either or both of
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the input files cannot be opened.
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<LI> If, at the end of the run, the two input files have
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not been proven to be identical, and the <SAMP>ABORT</SAMP>
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keyword is present, <SAMP>diff</SAMP> returns severe status.
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<LI> <SAMP>diff</SAMP> returns success status if none of the
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above conditions (or similar conditions) occur, even if the
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two files are different.
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<P>The <SAMP>diff</SAMP> command <I>appends</I> its
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differences report rather than merely writing it. This
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allows a regression test script to perform a series of
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regression tests and produce a report for the user.
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<P>The <SAMP>diff</SAMP> command was added to the shell after
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it had become apparent that the simpler <SAMP>compare</SAMP>
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command was not yielding enough information. Whereas early
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on, regression testing was treated mainly as a tool to
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ensure that FunnelWeb was being ported to other machines
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correctly, it began to place an increasing role during
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development in identifying the effects of changes made to
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the code. The <SAMP>diff</SAMP> command supports this
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application of regression testing by pinpointing the
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differences between nearly-identical text files.
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