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ignoring or replacing white lines in a diff

Nathan Hilterbrand nhilterbrand at gmail.com
Thu Jan 14 15:57:08 EST 2016 
On 01/14/2016 03:22 PM, Adriaan Renting wrote:
> Maybe someone here has a clue what is going wrong here? Any help is
> appreciated.
>
> I'm writing a regression test for a module that generates XML.
>
> I'm using diff to compare the results with a pregenerated one from an
> earlier version.
>
> I'm running into two problems:
>
> The diff doesn't seem to behave properly with the -B option. (diff (GNU
> diffutils) 2.8.1 on OSX 10.9)
>
> Replacing -B with -I '^[[:space:]]*$' fixes it on the command line,
> which should be exactly the same according to:
> http://www.gnu.org/software/diffutils/manual/html_node/Blank-Lines.html#Blank-Lines
>
> (for Python problem continue below)
>
> MacRenting 21:00-159> diff -w -B test.xml xml/Ticket_6923.xml
> 3,5c3,5
> <   <version>2.15.0</version>
> <   <template version="2.15.0" author="Alwin de Jong,Adriaan Renting"
> changedBy="Adriaan Renting">
> <   <description>XML Template generator version 2.15.0</description>
> ---
>>            <version>2.6.0</version>
>>            <template version="2.6.0" author="Alwin de Jong"
> changedBy="Alwin de Jong">
>>            <description>XML Template generator version
> 2.6.0</description>
> 113d112
> <
> 163d161
> <
> 213d210
> <
> 258d254
> <
> 369d364
> <
> 419d413
> <
> 469d462
> <
> 514d506
> <
> 625d616
> <
> 675d665
> <
> 725d714
> <
> 770d758
> <
> 881d868
> <
> 931d917
> <
> 981d966
> <
> 1026d1010
> <
> 1137d1120
> <
> 1187d1169
> <
> 1237d1218
> <
> 1282d1262
> <
>
> /Users/renting/src/CEP4-DevelopClusterModel-Story-Task8432-SAS/XML_generator/test
> MacRenting 21:00-160> diff -w -I '^[[:space:]]*$' test.xml
> xml/Ticket_6923.xml
> 3,5c3,5
> <   <version>2.15.0</version>
> <   <template version="2.15.0" author="Alwin de Jong,Adriaan Renting"
> changedBy="Adriaan Renting">
> <   <description>XML Template generator version 2.15.0</description>
> ---
>>            <version>2.6.0</version>
>>            <template version="2.6.0" author="Alwin de Jong"
> changedBy="Alwin de Jong">
>>            <description>XML Template generator version
> 2.6.0</description>
>
>
> Now I try to use this in Python:
>
>        cmd   = ["diff", "-w", "-I '^[[:space:]]*$'", "./xml/%s.xml" %
> name, "test.xml"]
>        ## -w ignores differences in whitespace
>        ## -I '^[[:space:]]*$' because -B doesn't work for blank lines
> (on OSX?)
>        p     = subprocess.Popen(cmd, stdin=open('/dev/null'),
> stdout=subprocess.PIPE, stderr=subprocess.PIPE)
>        logs  = p.communicate()
>        diffs = logs[0].splitlines() #stdout
>        print "diff reply was %i lines long" % len(diffs)
>
> This doesn't work. I've tried escaping the various bits, like the * and
> $, even though with single quotes that should not be needed.
>
> I tried first removing the blank lines from the file:
>
>        import fileinput
>        for line in fileinput.FileInput("test.xml",inplace=1):
>          if line.rstrip():
>            print line
>
> This makes it worse, as it adds and empty line for each line in the
> file.
>
> I've tried various other options. The only thing I can think of, is
> ditching Python and trying to rewrite the whole script in Bash.
> (It's quite complicated, as it loops over various things and does some
> pretty output in between and I'm not very fluent in Bash)
>
> Any suggestions?
>
> Thanks for any help provided.
>
> Adriaan Renting.
>
>
> Adriaan Renting        | Email: renting at astron.nl
> Software Engineer Radio Observatory
> ASTRON                 | Phone: +31 521 595 100 (797 direct)
> P.O. Box 2             | GSM:   +31 6 24 25 17 28
> NL-7990 AA Dwingeloo   | FAX:   +31 521 595 101
> The Netherlands        | Web: http://www.astron.nl/~renting/
>
>
Without having the files handy to test with, I would suggest that you 
try replacing "-I '^[[:space:]]*$'" with r"-I '^[[:space:]]*$'" as a 
starting point.

Nathan
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