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Old 11-10-2007, 02:40 AM   #1
RattleSn@ke
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Question [SOLVED] Problem changing line with sed. Should i use AWK?


Hi all!

I'm struggling with a problem with sed (or awk).
I have several different files which need a change on a certain line.
The files contain lines like:
B-1234/ 0001ABCD-0023ASDF-W-5--
The next file has a line like:
B-1234/ 0001ABCD-0023EFVB-W-5--

I need to find a way to change ASDF and EFVB into ABCD.
What I don't want is to search for the strings that has to be replaced, because they change over time.
What I want is to replace the 4 characters starting of position 22 with ABCD.

I'm searching for two days now but it seems I can't get hold of the right construction.

Please help me find the right construction.

TIA!
Onno.

Last edited by RattleSn@ke; 11-11-2007 at 05:48 AM.
 
Old 11-10-2007, 05:11 AM   #2
druuna
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Hi,

If I understand correctly, you only want to change positions 23 thru 26 with ABCD, no matter what the first 22 or the last 6 are. If that is the case:

sed 's/\(.\{21\}\)\(.*\)\(.\{6\}\)/\1ABCD\3/' infile

Example run:
Code:
$ cat infile 
B-1234/ 0001ABCD-0023ASDF-W-5--
B-1234/ 0001ABCD-0023EFVB-W-5--
W-4321/ 0431ABCD-0024ASDF-X-6--
W-4321/ 01A43BCD-0024EFVB-X-6--
Z-4477/ 3301ABCD-0025ASDF-Y-7--
Z-4477/ 3301ABCD-0025EFVB-Y-7--

$ sed 's/\(.\{21\}\)\(.*\)\(.\{6\}\)/\1ABCD\3/' infile 
B-1234/ 0001ABCD-0023ABCD-W-5--
B-1234/ 0001ABCD-0023ABCD-W-5--
W-4321/ 0431ABCD-0024ABCD-X-6--
W-4321/ 01A43BCD-0024ABCD-X-6--
Z-4477/ 3301ABCD-0025ABCD-Y-7--
Z-4477/ 3301ABCD-0025ABCD-Y-7--
It's up to you to figure out the sed command used If you cannot figure it out, just ask.

Hope this helps.
 
Old 11-10-2007, 07:32 AM   #3
pixellany
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Quote:
sed 's/\(.\{21\}\)\(.*\)\(.\{6\}\)/\1ABCD\3/' infile
Thereby proving that one can write totally inscrutable commands using SED.......

3 groups in "\()\" for backreference....loosely translated as:

group1: 21 of any character
group2: any # of characters
group3: 6 of any character

Replace with: group1 + ABCD + group3

Note that this will be VERY dependent on the format of the original file.

Another method would be to replace the 2nd group of 4 capital letters:

Quote:
sed 's/[A-Z]\{4\}/ABCD/2'
Even this is dependent on the exact structure of the file entries

Last edited by pixellany; 11-10-2007 at 08:23 AM. Reason: fixed boo-boo
 
Old 11-10-2007, 08:12 AM   #4
druuna
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Hi,

@pixellany: Shouldn't that be: Replace with: group1 + ABCD + group3

I do like the shorter example you give (keeping it 'as simple' as possible).
 
Old 11-10-2007, 08:22 AM   #5
pixellany
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Quote:
@pixellany: Shouldn't that be: Replace with: group1 + ABCD + group3
Of course!!! (fixed in the original)
 
Old 11-11-2007, 05:47 AM   #6
RattleSn@ke
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Many thanks guys!!

It indeed solved the 'problem'.
Now I'm changing the scripts so it will only update a certain line, because each file only contains one line like C-7906/ 0001AASU-0031DNGS-M-9-- and the rest of the file don't need any changes.
With the current command to many lines get changed.

So I'm going to use grep -i -n "<needle>" <haystack> to get the right linenumber and feed that one to the sed command!!

Thanks again!!
From a windy netherlands,
Onno.
 
Old 11-11-2007, 06:08 AM   #7
druuna
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Hi,

You probably can do that with one sed command (no need to use grep and sed). Something like this:

sed '/^C-4321/s/\(.\{21\}\)\(.*\)\(.\{6\}\)/\1ABCD\3/' infile will only change a line if it starts with C-4321

Wildcards are also possible:

$ sed '/^[ACE]/s/\(.\{21\}\)\(.*\)\(.\{6\}\)/\1ABCD\3/' infile This will change only those lines that start with an A, C or E.

Hope this helps.
 
Old 11-12-2007, 01:03 PM   #8
RattleSn@ke
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Thanks for the tip druuna.
But I still have to use grep since the lines start everytime with a different 'key'. I already changed my script and it's working without a hitch.

But thanks again!
Onno.
 
  


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