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<H3 align="left"><img src="../../gx/dennis/qbubble.gif"
height="50" width="60" alt="(?) " border="0"
>shell script</H3>
<p><strong>From Peter Truong on Mon, 28 Aug 2000
</strong></p>
<p align="right">Answered By: Ben Okopnik</p>
<P><STRONG><IMG SRC="../../gx/dennis/qbub.gif" ALT="(?)"
HEIGHT="28" WIDTH="50" BORDER="0"
>
I have a directory consisting of:
</STRONG></P>
<pre><strong>
test01.in test05.in test99.in <-- in files
test01.out test05.out test99.out <-- out files
</strong></pre>
<P><STRONG>
this is my code:
</STRONG></P>
<Pre><STRONG>
infile=`test[0-9][0-9]*.in`
outfile=`test[0-9][0-9]*.out`
</STRONG></Pre>
<BLOCKQUOTE><IMG SRC="../../gx/dennis/bbub.gif" ALT="(!)"
HEIGHT="28" WIDTH="50" BORDER="0"
>
This is at least one of the reasons it doesn't work. What you seem to
be trying to do here is create a list of files under the "$infile" and
"$outfile" labels <TT>-</TT> but by putting the right side of the equation in
backquotes, you're asking the shell to _execute_ it. That won't work;
in fact, you should get an error message when you run this.
</BLOCKQUOTE>
<Pre><STRONG><IMG SRC="../../gx/dennis/qbub.gif" ALT="(?)"
HEIGHT="28" WIDTH="50" BORDER="0"
>
for input in $infile
do
for output in $outfile
a.out < $input > $output
</STRONG></Pre>
<BLOCKQUOTE><IMG SRC="../../gx/dennis/bbub.gif" ALT="(!)"
HEIGHT="28" WIDTH="50" BORDER="0"
>
What this will do is execute "a.out" and use the current value of "$input"
as the file for it to process, then output the result into the filename
that is the current value of "$output" (overwriting whatever was in there
originally). You didn't mention this part of the script in your explanation
of what you want the script to do, but this _will_ wreck your "*.out"
files. This "double" loop will also repeat the above process as many times
as there are output files (if the original "list of files" equation worked)
for <EM>each</EM> input file, i.e., if you have 50 "*.in/*.out" pairs, the inside
loop will execute 2500 times <TT>-</TT> and the end result will be the "processed"
value of the last file in the "input" list written to every file in the
"output" list.
</BLOCKQUOTE>
<Pre><STRONG><IMG SRC="../../gx/dennis/qbub.gif" ALT="(?)"
HEIGHT="28" WIDTH="50" BORDER="0"
>
cmp $input $output
</STRONG></Pre>
<BLOCKQUOTE><IMG SRC="../../gx/dennis/bbub.gif" ALT="(!)"
HEIGHT="28" WIDTH="50" BORDER="0"
>
This part, of course, becomes useless after the above procedure: either
"a.out" changes "$input", in which case it will always be different, or
it does not change it, in which case it will always be identical.
</BLOCKQUOTE>
<Pre><STRONG><IMG SRC="../../gx/dennis/qbub.gif" ALT="(?)"
HEIGHT="28" WIDTH="50" BORDER="0"
>
echo $?
done
</STRONG></Pre>
<P><STRONG>
but this however, doesn't work.
what I want it to do is:
</STRONG></P>
<P><STRONG>
<ul>
<li> get each of the individual pairs of files (ie. test01.in & test02.out)
<li> and compare each pair until there is no more to compare.
</ul></STRONG></P>
<BLOCKQUOTE><IMG SRC="../../gx/dennis/bbub.gif" ALT="(!)"
HEIGHT="28" WIDTH="50" BORDER="0"
>
All right; try this -
</BLOCKQUOTE>
<BLOCKQUOTE><pre>
--------------------------------------------------------------------
#!/bin/bash
#
# "in_out" - compares all <fname>.in to <fname>.out files in the
# current directory
for n in *.in
do
cmp $n $(basename $n in)out
done
--------------------------------------------------------------------
</pre></BLOCKQUOTE>
<BLOCKQUOTE>
It's basic, but worth repeating: the "hash-bang" line comes first in any
shell script and must be contiguous (no spaces). If the script requires
input, write an error-checking routine and print usage instructions on an
error; otherwise, as in this one, comments will help you remember what it
does (you may remember it today, but not 3 years and 1,000 scripts down the
road.) Next, the loop <TT>-</TT> for each "in" file, we generate the "out" filenames
via "basename", by chopping off the "in" extension and tacking on an "out".
Then we perform the comparison and print a message for every pair that
fails: "cmp" exits silently on a "good" comparison, and prints a message on
a bad one. If you want numeric output, you can use "cmp <TT>-s</TT>" (for "silent"
output, i.e., it only sets the status flag) and "$?" to print the status
value.
</BLOCKQUOTE>
<BLOCKQUOTE>
Good luck with your shell-scripting,
<br>Ben Okopnik
</BLOCKQUOTE>
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