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Old 03-01-2005, 04:33 PM   #1
ojschubert
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help with sed


Hi,

I was wondering if someone could help get me started with sed.

I have a text document I'd like to edit. It basically looks like this:

row1: 04
row2: 93
row3: 40

I would like to change these numbers but not sure how to implement the sed command to do so.

Any help is appreciated

OJ
 
Old 03-01-2005, 04:39 PM   #2
dsegel
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How do you want to change them? Can you give a before and after example?
 
Old 03-01-2005, 04:46 PM   #3
ojschubert
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I just want to change those values. So for example:

Before edit

row1: 20
row2: 39
row3: 34


After edit

row1: 20
row2: 85
row3: 34

Basically I just want to change the numbers ( or are they charactesr in this case?) at the end of a line.
 
Old 03-01-2005, 04:50 PM   #4
dsegel
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sed -i 's/39$/85/' filename
 
Old 03-01-2005, 04:51 PM   #5
dsegel
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the '-i' parameter tells sed to edit the file in place. The 's' is the search/replace command, the $ means "match end of line", so '39$' is a match for 39 followed by a newline character. The second pair in // (/85/ in this case) is what to replace it with.

Last edited by dsegel; 03-01-2005 at 04:52 PM.
 
Old 03-01-2005, 05:12 PM   #6
ojschubert
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Cool, that seems easy enough. I have a couple of questions though.

What would I do if I only wanted to change the value of at the end row2: no matter what value it has? (ie. I don't need to find a specific number, i just need to update a value at the end of a row. Is there a way I can just go to that location and ovewrite whatever is there? Maybe using grep and gawk?

And with the command you just gave me, will I run into problems if there are multiple entries of the same number? Say if I wanted to change row2 from a 39 to 84 but row1 has a 39 as well.

Do these questions make sense?
 
Old 03-01-2005, 05:19 PM   #7
dsegel
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1. Do you mean you want to make updates based on row number and not the contents of the row? That's a little uglier but certainly possible, using head, tail, and grep maybe.

2. The command I listed will change all occurances that match the pattern specified. If you only want to change certain lines you need a way to specify only those lines. Is there anything else in the line that uniquely identifies the ones you want to change?

Post a more complete description/example of what you're trying to do.
 
Old 03-01-2005, 06:18 PM   #8
ojschubert
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1. Yes I want to make editions based on a row number and not the content.

2. Yes, I only want to change a specific line. The only thing specific to the line is the label "row#:"

Basically I have a c program which will calculate a number. This number is to be writen to the text file. And there is a specific spot for this result. This document is then copied to other computers. So the other computers know the result of a certain operation. To extract a certain number I use the grep and gawk commands. I think this is the command:
grep row2: filename.txt | gawk '{print$2}'

This gets the line for row2: and gets whatever is in the second column.

Now I just need a way to write something to a specific spot in the text document.

I figure using Linux commands will be much easier than what would have to be done in the C program.

Hope this helps clarify everything

OJ
 
  


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