Why is sed not able to process piped output from xpath? - macos

Question

While trying to run the following in Terminal in Mac OS Lion, rather than getting the first line as output, I simply get the output from xpath.
curl -s http://wordsmith.org/awad/rss1.xml | xpath //item/description | sed q
Outputs:
Found 1 nodes:
-- NODE --
<description>...</description>
Instead of:
Found 1 nodes:
Why is sed not able to process the output from xpath? What am I missing?

Answer 1

I don't have Mac OS but I can guess your problem. If I do the equivalent under Linux I get the following output:
$ curl -s http://wordsmith.org/awad/rss1.xml | xpath -e "//item/description" | sed q
Found 1 nodes in stdin:
-- NODE --
<description>Ending life for humane reasons, such as to avoid pain from an incurable condition.</description>
That's because part of the output is going to stdout and part is going to stderr. So if I redirect everything to stdout, I get this,
$ curl -s http://wordsmith.org/awad/rss1.xml | xpath -e "//item/description" 2>&1 | sed q
Found 1 nodes in stdin:

Answer 2

I do not have the exact answer, but I have come up against this exact problem. Although I was using awk not sed. The solution was setting the -q flag. Also you forgot the -e flag to identify the expression. This might have something to do with me being on ubuntu and you being on osx. but my output was the same.
so what you want is
curl -s http://wordsmith.org/awad/rss1.xml | xpath -q -e //item/description | sed q
SYNOPSIS
xpath [-s suffix] [-p prefix] [-q] -e query [-e query] ... [file] ...
-q
Be quiet. Output only errors (and no separator) on stderr.

Answer 3

On OSX 10.7.4
I am not exactly sure what you wanted as an output. I wanted to get rid of the STDERR ("Found X nodes ...") and only print out the actual item (the actual title and description). Hopefully this helps.
> cat wordsmith.sh
#!/bin/bash
/usr/bin/curl -s http://wordsmith.org/awad/rss1.xml > file.xml
title=`xpath file.xml //item/title 2> /dev/null | sed 's/<[^>]\*>//g'`
description=`xpath file.xml //item/description 2> /dev/null | sed 's/<[^>]*>//g'`
echo $title : $description
/bin/rm file.xml
> ./wordsmith.sh
versal : Universal; whole.

Answer 4

I have additional info that may provide more clarity to the question and even solve some problems, as it did mine. The errors encountered are partially related to the version of xpath that you are running.
The -q quiet flag is available on the version that I installed on my Ubuntu system via apt-get, but not available on the versions installed either on OSX or RHEL. There are also slight syntax differences between the versions like the order of the query and the input are reversed.
But the most helpful part is that you can copy an Ubuntu-installed version to the other systems and it works fine with the rest of the already installed xpath library. You need to have xpath installed and can then just migrate the core xpath script (usually at /usr/bin/xpath). Then you can take advantage of the extremely helpful -q parameter and skip the sed/regex post processing.

Answer 5

If you don't have the -q flag on OS X, you could comment out those lines that print "-- NODE --" and "Found x nodes". Something like this:
murphy:~ pdurbin$ diff -u /usr/bin/xpath5.12.orig /usr/bin/xpath5.12
--- /usr/bin/xpath5.12.orig 2012-12-06 06:29:14.000000000 -0500
+++ /usr/bin/xpath5.12 2014-05-15 14:32:14.000000000 -0400
## -48,17 +48,18 ##
}
if ($nodes->size) {
- print STDERR "Found ", $nodes->size, " nodes:\n";
+ #print STDERR "Found ", $nodes->size, " nodes:\n";
foreach my $node ($nodes->get_nodelist) {
- print STDERR "-- NODE --\n";
+ #print STDERR "-- NODE --\n";
print $node->toString;
+ print "\n";
}
}
else {
print STDERR "No nodes found";
}
-print STDERR "\n";
+#print STDERR "\n";
exit;
murphy:~ pdurbin$

Answer 6

A lot late, but I had a similar problem in a bash script recently in which I was trying to suppress "Found # nodes:" followed by "---NODE---" for every item returned, above the values the command was inserting into an array.
For example:
Found 9 nodes:
-- NODE --
-- NODE --
-- NODE --
-- NODE --
-- NODE --
-- NODE --
-- NODE --
-- NODE --
-- NODE --
Please select your option from the menu:
1) Option 1
2) Option 2
etc.
I fixed it by redirecting STDERR to 2>/dev/null in my xpath argument. This eliminated the "Found # nodes" and only returned the array I loaded into a select menu. Hope this helps whoever stumbles across this in the future.