[ale] sed head scratcher

[Jim Kinney]

On Tue, Aug 4, 2009 at 2:33 PM, JK<jknapka at kneuro.net> wrote:
> Jim Kinney wrote:
>> breakout the greybeards....
>>
>>
>> I have a pile of text lines that need to have a certain portion
>> transposed from upper case (windows dweebs did the hostnames) to lower
>> case.
>>
>> So many lines like:
>>
>> 192.168.0.2 MACHINE102
>> 192.168.3.4  MACHINE304 FredsBox
>> 10.0.2.3   MACHINE599  TestingSystemB
>> etc
>>
>> So varying IP address then varying spaces then upper case name with
>> digits then varying spaces and sometimes followed by other name with
>> mixed case.
>>
>> I want to ONLY lower case the names after the IP address, not anything
>> else in the line.
>>
>> Here's what I have so far:
>>
>> cat /etc/hosts | sed '/ [A-Z]{7}[0-9]{1,3}/ y/[A-Z]/[a-z]/'
>>
>> seems like it should work but it only replaces the 'A' with 'a' and it
>> does it anywhere in the line.
>
>
> Disclaimer 1: I just scrambled the keycaps on my laptop, so this message
> may make absolutely no sense whatsoever.
>
> Disclaimer 2: I Am Not A sed Expert, though I've used it on occasion
> (and have to re-read the manpage each time).
>
> That said:
>
> (1) First regexp selects lines to change, but does not restrict the
> scope of the following command within the selected lines.  The
> command itself, IIRC, must do the work to restrict itself to a particular
> region of interest within the line it's operating on. (Accomplishing
> this is left as an exercise for the reader, but I'm pretty sure that
> in this case it would involve capture groups in the "to change"
> regexp and capture-group backrefs in the replacement :-)
>
> (2) Assuming sed substitutions are like vi ones, wouldn't you need
> a "g" (global) qualifier to make the subst cmd do more than a single
> substitution?

My thinking as well. However:

cat testfile
ABCDEFGI01
BCDEFGHI02
ABCDFGHI01 little stuff
123 BSGXAAKI01 456
123.0.23.45 ABCDEFGI02 FredsPage


[jkinney at worktop tmp]$ cat testfile | sed -r '/[A-Z]{8}[0-9]{1,3}/
y/[QWERTYUIOPASDFGHJKLZXCVBNM]{8}[0-9]{1,3}/[qwertyuiopasdfghjklzxcvbnm]{8}[0-9]{1,3}/'
abcdefgi01
bcdefghi02
abcdfghi01 little stuff
123 bsgxaaki01 456
123.0.23.45 abcdefgi02 fredspage

It LC's all text yet it looks like the search field requires 1-3
digits. So the string "FredsPage" should not be altered.

>
> -- JK
>
>
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-- 
-- 
James P. Kinney III
Actively in pursuit of Life, Liberty and Happiness