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Old 12-12-2008, 01:55 PM   #1
FIRATYILDIRIM
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i am missing new lines when substituting with sed in a bash script


i have a file like

~ 4 ~ 2 ~ 4 ~
~ 11 ~ 2 ~ 4 ~
~ 2 ~ 2 ~ 4 ~

i want to substitute '~'s with '\t's and i am using

Code:
sed -e :a -e 's/~/\t/' "filename"
this is my first experiment with bash scripting so i did not write this on my own so i do not know what does this line doing too much but on the other hand it works great when it writes the result to screen and does what i want but when i write this to have result to a output file

Code:
echo `sed -e :a -e 's/~/\t/' "filename"` >> "filename"
it is writing them as only one line, not in three lines...

i need help

thanks for your time to read this
 
Old 12-12-2008, 02:22 PM   #2
pixellany
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There are several issues here:

1. The :a (label used for branching) does nothing in this context. Why is it there?

2. To replace ALL of the "~", you need the "g" flag--ie: sed 's/~/\t/g'

3. This construct: " sed <stuff> filename >> filename" Says: read from filename, apply the sed command, and append the result to filename. Thus, you wind up with the original content plus the modified content.

When I run it (with the g flag), the file winds up looking like this:
Code:
~ 4 ~ 2 ~ 4 ~
~ 11 ~ 2 ~ 4 ~
~ 2 ~ 2 ~ 4 ~
	 4 	 2 	 4 	
	 11 	 2 	 4 	
	 2 	 2 	 4
(Exactly what I would expect)

finally, the echo plus the command in backtics is not necessary---all you need is:
sed '<command>' file > newfile
OR
sed '<command>' file >> file
 
Old 12-12-2008, 02:23 PM   #3
pixellany
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go here for a good SED tutorial:
http://www.grymoire.com/Unix/Sed.html
 
Old 12-12-2008, 04:31 PM   #4
acid_kewpie
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See... sed guru.
 
Old 12-12-2008, 04:36 PM   #5
jschiwal
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Don't redirect the output to the same filename as the input. The file will be zeroed out before being read and you will end up with a zero length file. Either use a different file name or the "-i" "in place" option.
 
Old 12-12-2008, 06:01 PM   #6
pixellany
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Quote:
Originally Posted by acid_kewpie View Post
See... sed guru.
Where?....
 
Old 12-15-2008, 09:55 AM   #7
FIRATYILDIRIM
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thank you everybody who paid attantion and answered my question... my answer is late because i couldn't work on this code for a few day because of my exams (os & circuits )...

also thank you pixellany your sed 's/~/\t/g' code worked really good...

i saw you asked some question like i said i dont know how to write bash script too much... this is my first time... also i dont have too much time until to submit my experiment... (this is the experiment if someone is interested: ftp://ftp.cs.hacettepe.edu.tr/pub/de...5/Bil235-V.pdf)

also you have write.. the output you wrote is what i was getting... i think i had a little confusion while writing message... i am sorry for this...

thank you to everybody who spent time to write these messages...
 
Old 12-15-2008, 03:07 PM   #8
acid_kewpie
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hehe, well you managed to sneak homework past us which is pretty rare, so credit for being able to bend the rules without us noticing!
 
  


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