Using XPath in bash with not()

Question

This is follow-up to a previous question about using XPath in bash.

I have a set of XML files, most of which encode relations to other files:

<file>
    <fileId>xyz123</fileId>
    <fileContents>Blah blah Blah</fileContents>
    <relatedFiles>
        <otherFile href='http://sub.domain.abc.edu/directory/index.php?p=collections/pageview&amp;id=123‌​4'>
            <title>Some resource</title>
        </otherFile>
        <otherFile href='http://sub.domain.abc.edu/directory/index.php?p=collections/pageview&amp;id=4321'>
            <title>Some other resource</title>
        </otherFile>
    </relatedFiles>
</file>

The answer to the previous question helped me process the majority of these files successfully. However, there are some files in the set that do not include any relatedFiles/otherFile elements. I want to be able to process those files separately and move them into an "other" folder. I thought I could do this with an XPath not() function, but I get a "command not found" error for that line when I run the script.

#!/bin/bash

mkdir other
for f in *.xml; do
  fid=$(xpath -e '//fileId/text()' "$f" 2>/dev/null)   
  for uid in $(xpath -e '//otherFile/@href' "$f" 2>/dev/null | awk -F= '{gsub(/"/,"",$0); print $4}'); do
    echo  "Moving $f to ${fid:3}_${uid}.xml"
    cp "$f" "${fid:3}_${uid}.xml"    
  done      
  if $(xpath -e 'not(//otherFile)' "$f" 2>/dev/null); then            
    echo  "Moving $f to other/${fid:3}.xml"
    cp "$f" "other/${fid:3}.xml"              
  fi  
  rm "$f"    
done

How can I filter out files that do not contain certain elements using XPath in bash? Thanks in advance.

Answer 1

The $() construct substitutes the output of the command. As such, whatever is spit out by xpath will be substituted and the shell will try to execute that as a command which is why you get the error message.

Since xpath doesn't seem to provide a different exit code based on whether a node was found, you will probably just have to compare the output to something, or test for empty:

if [ -z "$(xpath -q -e '//otherFile' "$f" 2>/dev/null)" ]; then

This should execute the following code if xpath produced no output. To reverse the sense, use -n instead of -z (not sure which one you intended).