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Subject: DO NOT REPLY [Bug 51964] New: Documentation of RewriteRule flag skip
 unclear
Date: Wed, 05 Oct 2011 16:54:45 +0000
Message-ID: <bug-51964-56585@https.issues.apache.org/bugzilla/>
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https://issues.apache.org/bugzilla/show_bug.cgi?id=51964

             Bug #: 51964
           Summary: Documentation of RewriteRule flag skip unclear
           Product: Apache httpd-2
           Version: 2.3-HEAD
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Documentation
        AssignedTo: docs@httpd.apache.org
        ReportedBy: chealer@gmail.com
    Classification: Unclassified


The documentation of the skip flag of RewriteRule is unclear:
http://httpd.apache.org/docs/current/en/rewrite/flags.html#flag_s

The section reads:


The [S] flag is used to skip rules that you don't want to run. This can be
thought of as a goto statement in your rewrite ruleset. In the following
example, we only want to run the RewriteRule if the requested URI doesn't
correspond with an actual file.

# Is the request for a non-existent file?
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
# If so, skip these two RewriteRules
RewriteRule .? - [S=2]

RewriteRule (.*\.gif) images.php?$1
RewriteRule (.*\.html) docs.php?$1

This technique is useful because a RewriteCond only applies to the RewriteRule
immediately following it. Thus, if you want to make a RewriteCond apply to
several RewriteRules, one possible technique is to negate those conditions and
use a [Skip] flag. So, you can use this to make pseudo if-then-else constructs:
The last rule of the then-clause becomes skip=N, where N is the number of rules
in the else-clause.


Thanks to the example, I'm able to understand how it works. I understand the
analogy to goto, although goto-s do not take relative line numbers AFAIK, so
this could be clarified. The bit saying that "one possible technique is to
negate those conditions and use a [Skip] flag" could be clarified with "one
possible technique is to negate those conditions and to add a rule which uses a
[Skip] flag".

What I find really unclear is the analogy with if-then-else. I understand there
are conditions, so I see an equivalent of the if part. If the conditions do not
match, an else block is executed, so I see an equivalent here too. But I don't
see an equivalent to the then part. I don't understand the sentence "The last
rule of the then-clause becomes skip=N, where N is the number of rules in the
else-clause."
"The last rule of the then-clause becomes skip=N" is very unclear to me.

I suggest to add an example analogy to clarify, giving a pseudocode equivalent
to the snippet above, saying "If Apache configuration would support if
structures, we could have written something like: [...]. Instead, we write:
[snippet above]."

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