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Select value with Linux command xpath (from Perl)

Answer 1

A:

You want to separate the string based on the =, so use split (perldoc -f split):

my ($attr, $value) = split /=/, 'file="/var/lib/libvirt/images/save.raw"';

However, instead of parsing these values literally, you should use the many libraries of XML parsers, such as XML::XPath.

Ether 2009-12-09 21:51:19

Its the workaround I use now in my bashscript, splitting it litterally by using cut -d = -f 2, but i want to use the xpath function for it, something like $ virsh dumpxml save 2>/dev/null | xpath -e "value(/domain/devices/disk[@type='file']/source/@file[1])"...

falstaff 2009-12-09 22:24:21

Answer 2

A:

/domain/devices/disk[@type='file']/source/@file[1]/text()

Tomalak 2009-12-09 21:51:51

This gives me:$ virsh dumpxml save 2>/dev/null | xpath -e "/domain/devices/disk[@type='file']/source/@file[1]/text()"No nodes found in stdin

falstaff 2009-12-09 22:22:20

Hm, obviously naked text nodes cannot be processed/displayed. It was just a guess on my part, admittedly.

Tomalak 2009-12-09 23:42:55

Answer 3

A:

I think returning only the value is normal behaviour. Maybe it is a bug? I tried /text() like Tomalak suggested and it returns nothing (at least with this tool).
You could now pipe the output in another command like sed to get the desired result:

... | sed -r 's/.*?"(.*)"/\1/'

Edit:
Apparently the perl script uses XML::XPath and uses only find for the query which returns a NodeSet object. But there also is findvalue which the script doesn't use. Maybe you could fiddle around a little with the script. Only replacing find with findvalue gives just the value on stdout, but also error messages on stderr.
Doc for the library: http://search.cpan.org/~msergeant/XML-XPath-1.13/XPath.pm

andre-r 2009-12-09 22:11:20

Yeah its somewhat like I use now... I just would like to do it in the xpath way... cut -d = -f 2

falstaff 2009-12-09 22:26:17

Answer 4

+1 A:

I use (maybe because I wrote it ;--) xml_grep2, from App::xml_grep2, which has a convenient -t option that returns the text value of the result:

virsh dumpxml save | xml_grep2 -t "/domain/devices/disk[@type='file']/source/@file[1]"

should work

mirod 2009-12-09 22:58:34

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Select value with Linux command xpath (from Perl)

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