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Need help with sed to match and replace a string

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# 1  
Old 12-01-2014
Need help with sed to match and replace a string
friends I am struck in a situation where I need to comment a line start with space as below in a file

Code:
      root@LOCALHOST * rw
          LOCALHOST* r

I should comment second line only

Any help please
Last edited by Corona688; 12-01-2014 at 01:49 PM..
# 2  
Old 12-01-2014
Hello mallak,

Not sure as you haven't given any complete condition, following may help you(not tested though).

Code:
awk '/^ / {$0="#"$0} 1'  Input_file

Thanks,
R. Singh
Last edited by RavinderSingh13; 12-01-2014 at 02:13 PM.. Reason: Edited text
# 3  
Old 12-01-2014
Ravinder

Thanks for your response. I didn't got the expected result.

This is what I am trying to achieve

I have a file with many lines and among them Above are two lines.

Out of which I need to write a single liner so I can comment one line
# 4  
Old 12-01-2014
Please tell us the conditions to apply. Should it be the second line having LOCALHOST in it? The one with 9 spaces in front? The one without "root"? without "@"? "rw"?
How can we identify THAT line amongst the "many lines"?
# 5  
Old 12-01-2014
Thanks for the response

I could see the condition as a

Code:
[space]LOCALHOST[space]*[space]r

Replace it with

Code:
#LOCALHOST[space]*[space]r

Last edited by Scrutinizer; 12-01-2014 at 06:44 PM.. Reason: code tags
# 6  
Old 12-01-2014
This one allows leading whitespace (spaces or tabs).
$1 (the first field in the line) must begin with LOCALHOST.
Code:
awk '$1~/^LOCALHOST/ {$0="#"$0} {print}'

---------- Post updated at 03:00 PM ---------- Previous update was at 02:52 PM ----------

Some versions of sed can recognize character classes, then you can do
Code:
sed 's/^[[:space:]]*LOCALHOST/#&/'

# 7  
Old 12-01-2014
Quote:
Originally Posted by mallak
Thanks for the response

I could see the condition as a

[space]LOCALHOST[space]*[space]r

Replace it with

#LOCALHOST[space]*[space]r
This translates to e.g.
Code:
awk '/^ *LOCALHOST \* r$/ {sub(/^ */,"#"} 1' file

Sure that's what you want?

EDIT: It wouldn't work on your sample above for two reasons: a) no space after LOCALHOST b) <CR> chars as line terminators
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