| TechTip: Using Qshell from RPG to Compare Two Files |
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| Tips & Techniques - RPG | ||||||||||||||||||||||||||||||||
| Written by Aaron Bartell | ||||||||||||||||||||||||||||||||
| Tuesday, 04 September 2007 | ||||||||||||||||||||||||||||||||
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Qshell's cmp (compare) command can easily tell you whether two files are exactly the same. I have been on the System i for a number of years now, and it seems there is no end to the neat functionality I find on a regular basis to modernize and extend my existing applications. Most recently, I had a need to write some unit test scripts in RPG to compare a dynamically generated XML file to an existing XML document to determine whether or not they were exactly the same. I could have gone the route of coding everything in RPG using the IFS APIs, but I decided against that as the functionality already exists in Qshell's cmp (compare) command. By using the cmp command, I was able to interface with an API that has been tested by thousands of other developers, thus giving me a high level of confidence that the API will appropriately compare one file to another. Reusing what already exists is true SOA in action and is what we developers need to do to retain investment in our machines and take them to the next level in a fraction of the time.All right! Enough intro. Let's see some code! An obvious approach to using the Qshell APIs would be to first wrap them in an RPG program for ease of use. The example program below shows different parameters used to invoke the QSH_cmpSame RPG subprocedure.
H bnddir('GENBND') dftactgrp(*no)
/copy mcpress,QSHCp D result s n /free result = QSH_cmpSame('/home/aaron/compare1.txt': '/home/aaron/compare2.txt'); result = QSH_cmpSame('/home/aaron/compare1.txt': '/home/aaron/compare3.txt'); result = QSH_cmpSame( '/qsys.lib/aaronlib.lib/mcpress.file/compare1.mbr': '/qsys.lib/aaronlib.lib/mcpress.file/compare2.mbr'); result = QSH_cmpSame( '/qsys.lib/aaronlib.lib/mcpress.file/compare1.mbr': '/qsys.lib/aaronlib.lib/mcpress.file/compare3.mbr'); *inlr = *on; /end-free
The first line of interest is the /copy, where we bring in the prototype to make the call to QSH_cmpSame. The result variable is declared as a Boolean and will hold the result of each call to QSH_cmpSame.
/home/aaron/compare1.txt:
<xml>sometext</xml> /home/aaron/compare2.txt: <xml>sometext</xml> /home/aaron/compare3.txt: <xml>sometext and some more</xml> /qsys.lib/aaronlib.lib/mcpress.file/compare1.mbr: D var s 10a /qsys.lib/aaronlib.lib/mcpress.file/compare2.mbr: D var s 10a /qsys.lib/aaronlib.lib/mcpress.file/compare3.mbr: D var s 20a The following code shows the contents of QSH_cmpSame. The first thing that needs to happen is the redirecting of what's called standard input, standard output, and standard error. Subroutine SetupIO opens files with specific descriptors to do the Qshell redirection. (Go to the LiveFireLabs site for a good, concise tutorial of UNIX file descriptors.) You could think of the redirecting being similar to an OVRDBF used to alter the member used when accessing a PF for I/O.
//----------------------------------------------------------------------
// Author: Aaron Bartell // Copyright 2007 MowYourLawn.com All Rights Reserved. // // Compile: // CRTRPGMOD // MODULE(MYLIB/QSHFN) // SRCFILE(MYLIB/MCPRESS) // SRCMBR(QSHFN) // // CRTSRVPGM // SRVPGM(MYLIB/QSHSV) // MODULE(MYLIB/QSHFN) // SRCFILE(MYLIB/MCPRESS) // // After creating the service program you will need to add it to the // binding directory of your choice and then reference that binding // directory below (i.e. replacing GENBND). //---------------------------------------------------------------------- H nomain bnddir('QC2LE': 'GENBND') /copy mcpress,QSHCp D QzshSystem PR 10I 0 extproc('QzshSystem') D command * value options(*string) D close PR 10I 0 extproc('close') D handle 10I 0 value D unlink PR 10i 0 extproc('unlink') D path * Value options(*string) D open PR 10I 0 extproc('open') D filename * value options(*string) D openflags 10I 0 value D mode 10U 0 value options(*nopass) D codepage 10U 0 value options(*nopass) D stat pr 10i 0 extproc('stat') D filename * value options(*string) D statStruct * value D SDS D dsJobNo 264 269A D stsBuff ds align inz qualified D perms 10u 0 D fileID 10u 0 D linkCount 5u 0 D userIDNbr 10u 0 D groupIdNbr 10u 0 D bytesInFile 10i 0 D timeLastAcc 10i 0 D timeLastChg 10i 0 D timeStsLastChg... D 10i 0 D fileSysID 10u 0 D blockSize 10u 0 D allocBytes 10u 0 D objectType 11 D codePage 5u 0 D 62 D generationID 10u 0 //------------------------------------------------------------------------ // QSH_cmpSame //------------------------------------------------------------------------ P QSH_cmpSame B export D QSH_cmpSame PI 1n D pFile1 1024a varying const D pFile2 1024a varying const D O_RDONLY C 1 D O_WRONLY C 2 D O_CREAT C 8 D O_TRUNC C 64 D cmd S 2053A varying D msg S 52A D x S 10I 0 D rc1 s 10i 0 D rc2 s 10i 0 D result s n D stsBuff1 ds likeds(stsBuff) D stsBuff2 ds likeds(stsBuff) /FREE result = *off; exsr setupRedirect; if msg <> *blanks; return *off; endif; cmd = 'CMP ' + %trim(pFile1) + ' ' + %trim(pFile2); rc1 = QzshSystem(cmd); // Success is anything greater than -1. if rc1 < 0; return *off; endif; rc1 = stat('/tmp/stdout-'+dsJobNo: %addr(stsBuff1)); rc2 = stat('/tmp/stderr-'+dsJobNo: %addr(stsBuff2)); exsr closeRedirect; if stsBuff1.bytesInFile > 0 or stsBuff2.bytesInFile > 0 or rc1 < 0 or rc2 < 0; result = *off; else; result = *on; endif; return result; //------------------------------------------------------------------------ // File descriptors 0, 1 & 2 are used by unix-environments for // stdin, stdout & stderr. Redirect those 3 descriptors to stream files. //------------------------------------------------------------------------ begsr setupRedirect; for x = 0 to 2; callp close(x); endfor; msg = *blanks; // open up 0, 1, 2 as files. if open('/dev/qsh-stdin-null': O_RDONLY) <> 0; msg = 'Unable to redirect STDIN'; endif; if open('/tmp/stdout-'+dsJobNo: O_WRONLY+O_CREAT+O_TRUNC: 511) <> 1; msg = 'Unable to redirect STDOUT'; endif; if open('/tmp/stderr-'+dsJobNo: O_WRONLY+O_CREAT+O_TRUNC: 511) <> 2; msg = 'Unable to redirect STDERR'; endif; // Error occurred!!! if msg <> *blanks; dsply '' ' ' msg; exsr closeRedirect; endif; endsr; //------------------------------------------------------------------------ // Close the descriptors opened by setupIO //------------------------------------------------------------------------ begsr closeRedirect; for x = 0 to 2; callp close(x); endfor; unlink('/tmp/stdout-'+dsJobNo); unlink('/tmp/stderr-'+dsJobNo); endsr; /END-FREE P e
The second piece of interesting code is the composing of the CMP command and the subsequent calling of QzshSystem to process it. Exhaustive information on the QzshSystem API can be found here. But for the sake of layman conversation, it's simply an enabler of sorts that allows the execution of commands you would traditionally enter into a Qshell prompt interactively. To run an interactive Qshell session, simply enter STRQSH on the command line. You can find detailed information about the CMP here, but essentially, it simply does a byte-for-byte binary comparison of two files; and as I found out, it can also work in the QSYS.LIB side of the IFS. Additional References
Article: "TechTip: Qshell vs. PASE" |
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