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#23635
possible bug in \c escape handling
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Your bug report
#23635: possible bug in \c escape handling
which was filed against the sed package, has been closed.
The explanation is attached below, along with your original report.
If you require more details, please reply to 23635 <at> debbugs.gnu.org.
--
23635: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=23635
GNU Bug Tracking System
Contact help-debbugs <at> gnu.org with problems
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On Sat, May 28, 2016 at 8:40 PM, Jim Meyering <jim <at> meyering.net> wrote:
> On Sat, May 28, 2016 at 7:31 PM, Assaf Gordon <assafgordon <at> gmail.com> wrote:
>> Hello,
>>
>> Thank you for the review.
>> Attached an improved version.
>>
>> Regarding when the bug was introduced (in the 'NEWS'), version 3.02 did not support \c escapes, and version 4.0.6 had this bug (as does the first git commit). I wrote:
>> [bug introduced in the sed-4.0.* releases]
>
> Thanks for the quick update!
> One more thing I noticed is that you use here docs
> that interpolate. Just as I prefer to use single-quoted strings
> most of the time, e.g., to avoid having to backslash-escape
> every backslash, I prefer to use quoted here docs as in the
> attached. Also, I prefer to space-delimit operators like '<', '<<', and '>'.
> At least on one side.
>
> Also, I removed a stray "EOF" after the final "Exit..." line.
>
> Here's the proposed delta, on top of your patch:
I've pushed your patch amended with that change, and tweaked the log
message to have these lines: capitalized first word of each sentence
and added the (T) and (Bug fixes) qualifiers:
* sed/compile.c: (RECURSIVE_ESCAPE_C): New error message.
(normalize_text): Check for \c-backslash, reject recursive escaping.
* testsuite/recursive-escape-c.sh: New file. Test new behaviour.
* testsuite/Makefile.am (T): Add new test.
* NEWS (Bug fixes): Mention it.
Thanks again.
As I write this, I realized that I should have referenced the bug
report URL in the commit log. Oh well.
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Hello,
There might be a small bug in processing of GNU extension escape sequence "\c".
When the character following "\c" is a backslash, the code consumes only one character, leading to inconsistent and incorrect output.
Example:
$ echo a | sed 's/./\c\\/' | od -c
0000000 034 \ \n
0000003
$ echo a | sed 's/./\c\d/' | od -c
0000000 034 d \n
0000003
but:
$ echo a | sed 's/./\c\/' | od -c
sed: -e expression #1, char 8: unterminated `s' command
0000000
Meaning there is no way to generate the character '\x034' alone with "\c".
This is also somewhat inconsistent because it consumes a single backslash character
(whereas everywhere else a single backslash is the escape character itself).
For comparison, other characters behave as expected:
$ sed 's/./\cA/' in | od -c
0000000 001 \n
0000002
$ sed 's/./\c[/' in | od -c
0000000 033 \n
0000002
$ sed 's/./\c]/' in | od -c
0000000 035 \n
0000002
As a side effect, it could also be confusing if the syntax allows 'recursive' escapes,
such as "\c\x41", which might be argued to be '\c' of the following character,
which should be first evaluated as \x61, resulting in "\cA".
The attached patch fixes the problem with the following rules:
1. '\c\\' = Control-Backslash = ASCII 0x34.
2. Any other backslash combinations after "\c" are rejected, and sed aborts.
Tests included. comments are welcomed.
- assaf
[0001-sed-reject-recursive-escaping-after-c.patch (text/x-patch, attachment)]
This bug report was last modified 9 years and 50 days ago.
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