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====== Running gdxxrw only, if a spreadsheet has been changed ======
Q: //Hi, for my model I have to import data from different spreadsheets using gdxxrw. Is there a way to call gdxxrw only, if the particular spreadsheet has been changed? If it has not been changed, I just want to use the old gdx file, because in that case the import is much faster..//

**Distribution 23.1** introduced the new GDXXRW option ''CheckDate'' to regenerate output only if the input file is more recent than output file. 
<code>
c:\temp>gdxxrw.exe i=test.xls o=test.gdx Checkdate

GDXXRW           Jul 13, 2009 23.1.2 WIN 11128.12235 VIS x86/MS Windows
Input file : c:\temp\test.xls
Output file: c:\temp\test.gdx
No new file written (CheckDate is active)
Total time = 295 Ms
c:\temp>
</code>

**Older distributions:**

A quick and simple test, whether a particular spreadsheet is older than the corresponding  gdx file can be done using the program [[http://unixhelp.ed.ac.uk/CGI/man-cgi?test|test]], 
which is included in the GAMS Unix utilities. The example below is based on the model [[http://www.gams.com/modlib/libhtml/herves.htm|herves]] from the [[http://www.gams.com/modlib/modlib.htm|GAMS model library]]:<code>
* Only read from spreadsheet if XLS file is more recent than GDX file
$call =test "%gdx%" -nt "%xls%"
$if not errorlevel 1 $goto skipgdxxrw
$call gdxxrw "%xls%" output="%gdx%" par=raw rng="%rng%" rdim=2 cdim=1 set=rr rng="%rows%" rdim=2 values=NoData trace=2

$label skipgdxxrw
$gdxin "%gdx%"    // open GDX file
...
</code>

A more compact version is: 
<code>
* Only read from spreadsheet if XLS file is more recent than GDX file
$call test "%gdx%" -nt "%xls%" || gdxxrw "%xls%" output="%gdx%" par=raw rng="%rng%" rdim=2 cdim=1 set=rr rng="%rows%" rdim=2 values=NoData trace=2
$gdxin "%gdx%" // open GDX file
...
</code>
With more sophisticated dependencies between your input files you can use a Makefile and the UNIX [[http://www.opussoftware.com/tutorial/TutMakefile.htm|make]] program, which is also included in the GAMS Unix utilities:
<code>
$onecho > "%gams.scrdir%Makefile.scr"
%gdx%: %xls%
%system.tab%gdxxrw "%xls%" output="%gdx%" par=raw rng="%rng%" rdim=2 cdim=1 set=rr rng="%rows%" rdim=2 values=NoData trace=2
$offecho
* empty rows will be reported
$call =make -f "%gams.scrdir%Makefile.scr"
$if errorlevel 1 $abort Something wrong with reading raw data from %xls%

$label skipgdxxrw
$gdxin "%gdx%"    // open GDX file
$load raw rr      // load data into gams
$gdxin            // close gdx file 
</code>
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