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Re: shopt igncr not working

Larry Hall (Cygwin) wrote:
On 10/12/2006, Rob Walker wrote:
If you're referring to the performance gain realized, I think it could have been accomplished (if not as trivially) without breaking CRLF handling. This seems to be indicated in other posts, ones that talk about reworking line parsing.

I believe the response to this is <>. In other
words, if your belief is strong enough and you have the knowledge to back up
that belief, you just need the persistence to follow through on all that to
show everyone your concrete ideas. Since we've had allot of opinionated
discussions on topics like this from the uninformed or those who lack the
conviction to actually submit a patch to back up their point of view, it's
important to realize here that patches speak louder than words (hm, PSLTW -
acronym alert? ;-) )

Actually, though, I was asking about a bigger-picture strategy. One that appears to be steering Cygwin away from interoperability of the past, towards a more rigid interpretation of what Cygwin's suitable uses are. Do you have a set of guiding principles you consult when deciding the fate of Cygwin? Who do you consider Cygwin's customers to be?

The basic strategy is that in cases where decisions have to be made between
supporting Linux-like behavior or Windows conventions, err on the side
of Linux. Since the tools are meant to support the Linux way of doing
things, it's important they do. Otherwise people who are looking for and
expecting this behavior are left out.

Are you saying that these people expect bash to treat CRLF as if the CR were non-whitespace? Can you give me an example where this would be a useful feature?

They are the ones these tools are
built to support. That said, support for various Windows ways and conventions
are supported by default and when they don't conflict with the above. But
when there is a conflict, Linux-like behavior is the goal.
I guess you're saying (in this case) that the performance benefit of barfing on CRLF outweighs the usefulness of bash's invisible handling of CRLF?

To test this assertion, I benchmarked bash (3.1-9). The script I used to test is essesntially empty, with nothing but the shebang, a call to shopt, and 50k empty lines. I chose empty lines to keep bash's other complexities out of the picture. I only wanted to measure is how long it takes bash to parse lines.

Here are my results:

line ending  | mount mode | igncr | time ./
             |            |       | real    0m4.219s
CRLF         |  text      |  set  | user    0m0.983s
             |            |       | sys     0m3.202s
             |            |       | real    0m4.312s
CRLF         |  text      | clear | user    0m1.062s
             |            |       | sys     0m3.265s
             |            |       | real    0m2.109s
 LF          |  text      |  set  | user    0m0.608s
             |            |       | sys     0m1.499s
             |            |       | real    0m2.125s
 LF          |  text      | clear | user    0m0.592s
             |            |       | sys     0m1.546s
             |            |       | real    0m2.125s
CRLF         |  bin       |  set  | user    0m0.546s
             |            |       | sys     0m1.530s
             |            |       |
CRLF         |  bin       | clear | Whoops!
             |            |       |
             |            |       | real    0m2.188s
 LF          |  bin       |  set  | user    0m0.608s
             |            |       | sys     0m1.546s
             |            |       | real    0m2.141s
 LF          |  bin       | clear | user    0m0.640s
             |            |       | sys     0m1.515s

My conclusions:

1) CRLF vs. LF line endings have essentially no effect on the performance of this version of bash, even on a test where bash is doing nothing but handling linefeeds.
2) Ignoring CR on a binmode mount has no performance penalty over a clean LF-only file. In fact, the margin of error in this test was higher than the performance penalty.
3) CRLF on a text mode mount is really, really bad. This isn't bash's fault (note the time spent in user mode is the same as on binary mounts, all the time is spent in sys), and so to me looks like a non-solution to the problem of bash not handling CRLF; to say nothing of the other issues with text mode mounts.

Looks like making igncr the default in Cygwin is a no-cost solution in terms of performance, and a big win for compatibility.

Has anyone else done anything like this? Any flaws in my analysis?

Thanks for reading.


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