"[SOLVED] regex processing bug?"

tennenrishin

Why would the following process output 'a/b/c' rather than just 'c'?

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<process version="5.2.008">
  <context>
    <input/>
    <output/>
    <macros/>
  </context>
  <operator activated="true" class="process" compatibility="5.2.008" expanded="true" name="Process">
    <process expanded="true" height="659" width="1042">
      <operator activated="true" class="set_macro" compatibility="5.2.008" expanded="true" height="76" name="Set Macro" width="90" x="45" y="75">
        <parameter key="macro" value="path"/>
        <parameter key="value" value="a/b/c"/>
      </operator>
      <operator activated="true" class="generate_macro" compatibility="5.2.008" expanded="true" height="76" name="Generate Macro" width="90" x="179" y="75">
        <list key="function_descriptions">
          <parameter key="path_ending" value="replaceAll(&quot;%{path}&quot;,&quot;^.*/(?=[^/]+^)&quot;,&quot;&quot;)"/>
        </list>
      </operator>
      <operator activated="true" class="print_to_console" compatibility="5.2.008" expanded="true" height="76" name="Print to Console" width="90" x="313" y="75">
        <parameter key="log_value" value="OUTPUT: %{path_ending}"/>
      </operator>
      <connect from_op="Set Macro" from_port="through 1" to_op="Generate Macro" to_port="through 1"/>
      <connect from_op="Generate Macro" from_port="through 1" to_op="Print to Console" to_port="through 1"/>
      <portSpacing port="source_input 1" spacing="0"/>
      <portSpacing port="sink_result 1" spacing="0"/>
    </process>
  </operator>
</process>

Am I missing something obvious or might this be a bug?

haddock

Hi there,

I think that you are missing two things, '[' and ']', and that this is not a bug. Check this out..

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<process version="5.2.003">
  <context>
    <input/>
    <output/>
    <macros/>
  </context>
  <operator activated="true" class="process" compatibility="5.2.003" expanded="true" name="Process">
    <process expanded="true" height="383" width="763">
      <operator activated="true" class="set_macro" compatibility="5.2.003" expanded="true" height="76" name="Set Macro" width="90" x="45" y="75">
        <parameter key="macro" value="path"/>
        <parameter key="value" value="a/b/c"/>
      </operator>
      <operator activated="true" class="generate_macro" compatibility="5.2.003" expanded="true" height="76" name="Generate Macro" width="90" x="179" y="75">
        <list key="function_descriptions">
          <parameter key="path_ending" value="replaceAll(&quot;%{path}&quot;,&quot;[/]&quot;,&quot;oops &quot;)"/>
        </list>
      </operator>
      <operator activated="true" class="provide_macro_as_log_value" compatibility="5.2.003" expanded="true" height="76" name="Provide Macro as Log Value" width="90" x="313" y="75">
        <parameter key="macro_name" value="path_ending"/>
      </operator>
      <operator activated="true" class="log" compatibility="5.2.003" expanded="true" height="76" name="Log" width="90" x="447" y="75">
        <list key="log">
          <parameter key="m" value="operator.Provide Macro as Log Value.value.macro_value"/>
        </list>
      </operator>
      <connect from_op="Set Macro" from_port="through 1" to_op="Generate Macro" to_port="through 1"/>
      <connect from_op="Generate Macro" from_port="through 1" to_op="Provide Macro as Log Value" to_port="through 1"/>
      <connect from_op="Provide Macro as Log Value" from_port="through 1" to_op="Log" to_port="through 1"/>
      <connect from_op="Log" from_port="through 1" to_port="result 1"/>
      <portSpacing port="source_input 1" spacing="0"/>
      <portSpacing port="sink_result 1" spacing="0"/>
      <portSpacing port="sink_result 2" spacing="0"/>
    </process>
  </operator>
</process>

Best wishes,

H

tennenrishin

Hi H

Thank you for your response, but I don't understand. regexpal.com agrees that ^.*/(?=[^/]+^) matches the a/b/ in a/b/c

So I would expect the output in the OP to be c rather than a/b/c

Can you explain why you hold that a/b/c is the correct output?

Thanks
Isak

haddock

Hi,

Regex formulae may not uniquely satisfy, different methods can also work; on your problem you can achieve a/b/c -> c with a regex match of [/ab], which makes a list of matchable characters, like this..

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<process version="5.2.003">
  <context>
    <input/>
    <output/>
    <macros/>
  </context>
  <operator activated="true" class="process" compatibility="5.2.003" expanded="true" name="Process">
    <process expanded="true" height="383" width="763">
      <operator activated="true" class="set_macro" compatibility="5.2.003" expanded="true" height="76" name="Set Macro" width="90" x="45" y="75">
        <parameter key="macro" value="path"/>
        <parameter key="value" value="a/b/c"/>
      </operator>
      <operator activated="true" class="generate_macro" compatibility="5.2.003" expanded="true" height="76" name="Generate Macro" width="90" x="179" y="75">
        <list key="function_descriptions">
          <parameter key="path_ending" value="replaceAll(&quot;%{path}&quot;,&quot;[/ab]&quot;,&quot;&quot;)"/>
        </list>
      </operator>
      <operator activated="true" class="provide_macro_as_log_value" compatibility="5.2.003" expanded="true" height="76" name="Provide Macro as Log Value" width="90" x="313" y="75">
        <parameter key="macro_name" value="path_ending"/>
      </operator>
      <operator activated="true" class="log" compatibility="5.2.003" expanded="true" height="76" name="Log" width="90" x="447" y="75">
        <list key="log">
          <parameter key="m" value="operator.Provide Macro as Log Value.value.macro_value"/>
        </list>
      </operator>
      <connect from_op="Set Macro" from_port="through 1" to_op="Generate Macro" to_port="through 1"/>
      <connect from_op="Generate Macro" from_port="through 1" to_op="Provide Macro as Log Value" to_port="through 1"/>
      <connect from_op="Provide Macro as Log Value" from_port="through 1" to_op="Log" to_port="through 1"/>
      <connect from_op="Log" from_port="through 1" to_port="result 1"/>
      <portSpacing port="source_input 1" spacing="0"/>
      <portSpacing port="sink_result 1" spacing="0"/>
      <portSpacing port="sink_result 2" spacing="0"/>
    </process>
  </operator>
</process>

cf. http://www.lunametrics.com/blog/2006/10/22/regular-expressions-part-viii-square-brackets-and-dashes/

Best

H

PS I'm a great fan of RegexBuddy, which I think is related to the source you used; it has an explain feature - you put in your regex, and out comes an interpretation. Here's what it said about your first..

regexbuddy says.. ^.*/(?=[^/]+^) Options: ^ and $ match at line breaks Assert position at the beginning of a line (at beginning of the string or after a line break character) «^» Match any single character that is not a line break character «.*»   Between zero and unlimited times, as many times as possible, giving back as needed (greedy) «*» Match the character “/” literally «/» Assert that the regex below can be matched, starting at this position (positive lookahead) «(?=[^/]+^)»   Match any character that is NOT a “/” «[^/]+»       Between one and unlimited times, as many times as possible, giving back as needed (greedy) «+»   Assert position at the beginning of a line (at beginning of the string or after a line break character) «^» Created with RegexBuddy

and here's what it said about my second..

regexbuddy says.. [/ab] Options: ^ and $ match at line breaks Match a single character present in the list “/ab” «[/ab]» Created with RegexBuddy

tennenrishin

I am not asking for a regex that matches a/b/. (That's trivial - a/b/ is a regex that matches a/b/.)
a/b/c was just an example string that I happened to use, but it could just as well have been
i/know/what/my/regex/does in which case I want a match on i/know/what/my/regex/

But thanks anyway for discussing because typing out these responses revealed a typo in my regex. The regex of my intention was
^.*/(?=[^/]+$) rather than ^.*/(?=[^/]+^)

Now it all works.