Thursday, May 26, 2011

Re: modifying hex codes with a regex replace

I'm assuming the extra \ beginning each line refer to the sed "continue line" command.  I'm omitting them when putting it into gvim in a continuous line. 
 
This worked almost perfectly, but it replace all my instances of ^@ with the carriage return (\x0a). 
When using hex escapes, sometimes the escaped characters are not inserted, yielding the replacement string:
 
=2^Z^Y
 
 
Any ideas? 
 
Dylan
 
On Thu, May 26, 2011 at 9:26 AM, Ben Schmidt <mail_ben_schmidt@yahoo.com.au> wrote:
O, right!

You just have to use an expression in the subsitute part (using \=), and
nr2char(), char2nr() and submatch(). Whether you use literal characters
or hex escapes (\x, \%x etc.) doesn't matter. But something like this
should work:


:s!\%x00Heading level 1\%x00\+.\{-}\%x00\+\(\d\+\)\%x00\+
\Body text\%x00vel 1\%x00\+\(\_.\)[\x04\x01\x00]\+!
\\="\x00Body text\x00vel 2\x00\x00".nr2char(char2nr(submatch(2))+4).

\"\x00\x00\x19#".submatch(1)."\x1a"

HTH,

Ben.




On 27/05/11 12:02 AM, Dylan Evans wrote:
I don't believe I expressed the problem very well.  My regular expressions works
perfectly except for string 2.  String 2 reads in a single character.  I then need
to write out a different character, which is related to string 2 by having a hex
value 4 more than what was read.  For instance, if string two was an "a", (hex
code 61), I would need to print out an "e" (hex code 65), because 61 + 4 = 65.  I
would like to do this in gvim because I don't have access to a Perl compiler on
the windows machine that will be performing this task.
Thanks again

On Wed, May 25, 2011 at 8:27 PM, Ben Schmidt <mail_ben_schmidt@yahoo.com.au
<mailto:mail_ben_schmidt@yahoo.com.au>> wrote:

   On 26/05/11 1:34 AM, Floobit wrote:

       I'm trying to modify a series of binary files made with a legacy
       program, and need to change a certain character in my search string to
       the character with hex code +4.  For context, here is my sed regex:

       :s!^@Heading level 1^@\+.\{-}^@\+\(\d\+\)^@\+Body text^@vel 1^@\+\(\_.
       \{1}\)[^D^A^@]\+!^@Body text^@vel 2^@^@\2^@^@^Y#\1^Z

       with HEX(^@) =00, etc.  String 2 is only 1 character long, but is
       occasionally rendered as a carriage return, thus the need for the \_.
       \{1} pattern.  Instead of writing the exact character of string 2, I
       need to write the character +4 to its hex code.  For instance, if
       HEX(string2)=97, I would need to print ASCII(9b).


   To match it, either put it in directly (type Ctrl-V then Ctrl-D to get
   ^D, for example) or match with \%x outside a collection ( :help /\%x )
   or just \x inside a collection ( :help /\] ).

   To include it in the substitution, either put it in directly (except
   there are a few oddities, e.g. with \n or ^J representing null--:help
   sub-replace-special) or use an expression (:help sub-replace-expression)
   which can use nr2char() (:help nr2char()) or \x in a string (:help
   expr-string).

   Here's one option, avoiding using control characters, which means it's
   robust in something like .vimrc as encoding changes won't come into
   play, it turns out something like this:

   :s!\%x00Heading level 1\%x00\+.\{-}\%x00\+\(\d\+\)\%x00\+
   \Body text\%x00vel 1\%x00\+\(\_. \)[\x04\x01\x00]\+!
   \\="\x00Body text\x00vel 2\x00\x00".submatch(2).
   \"\x00\x00\x19#".submatch(1)."\x1a"

   (The backslashes at the beginnings of lines are just for line
   continuation if including in a .vimrc or script; omit them if you're
   joining the lines together, e.g. on the commandline.)

   I have no idea why you would use \{1}, so I omitted it, too. I may have
   made a bunch more booboos if I didn't understand the original regex
   (e.g. because sed has differences to Vim, which I know it does, but am
   not sure on any specifics).

   There are many, many other possible ways of achieving the same, too, so
   the above is just one opinion....

   Ben.





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