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sed command problem

 
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# 1  
Old 04-23-2014
sed command problem
Hi

i am reading a tutorial on sed
below command was given in tutorial. i am not able to understand the working of below command also this command is now working in my enviroment.

Code:
$ sed -n '1~2p' alarm
sed: 1: "1~2p": invalid command code ~
$


need your assitance here
# 2  
Old 04-23-2014
Hello,

I think it should be as follows.

Code:
sed -n '1,2p'  file_name

To print the first two lines.



Thanks,
R. Singh
# 3  
Old 04-23-2014
~ is a GNU extension, so your need GNU sed for that. m~n means match every n'th line starting with line m. Used like this, it means print every other line, starting with the first line. The same can be achieved in any sed like this:
Code:
sed -n 'p;n' file_name

This User Gave Thanks to Scrutinizer For This Post:
jim mcnamara
# 4  
Old 04-23-2014
The printing every other line thing is a bit of a tangle. When people give you this requirement, they may mean start with line 1, or possibly line 2. Printing odd-numbered lines vs. even-numbered lines.

Scrutinizer's code works either way. His example gives odd numbers, changing to
Code:
sed -n 'n;p' file_name

gives even numbers.
# 5  
Old 04-24-2014
Hi

the suggested command still not working

Code:
 
$ sed -n 'p:n' alarm 
sed: 1: "p:n": extra characters at the end of p command
$

scriptor

below snippet takem from online tutorial which i am using for learning sed

Code:
 
If we want to print every other line, we can specify the interval after the "~" character. The following line will print every other line starting with line 1: 
sed -n '1~2p' BSD

can ypu please explain me this line also . what does it mean here
Code:
If we want to print every other line,

by saying every other line i am not getiing their point
Last edited by scriptor; 04-24-2014 at 01:56 AM.. Reason: adding some more info
# 6  
Old 04-24-2014
That should be a ; not a :. sed -n 'p;n' , not sed -n 'p:n'
# 7  
Old 04-24-2014
thx working now .

substitute command is not working

here i am replacing foo with bar .
Code:
 
sed 's/foo/bar' f1

 
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