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sed command to Insert a line before the last four lines of the file

 
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# 1  
Old 09-18-2015
sed command to Insert a line before the last four lines of the file
By using sed command, How to insert a new line before the last four lines of the file.

Code:
Old Line
Old Line
NEW LINE!
Old Line
Old Line
Old Line
Old Line

Last edited by wridler; 09-18-2015 at 07:36 AM.. Reason: code tags
# 2  
Old 09-18-2015
Hi,
Example:
Code:
$ cat file.txt
Old Line
Old Line
Old Line
Old Line
Old Line
Old Line
$ tac file.txt | sed -e '5iNEW LINE!' | tac
Old Line
Old Line
NEW LINE!
Old Line
Old Line
Old Line
Old Line

Regards.
This User Gave Thanks to disedorgue For This Post:
Don Cragun
# 3  
Old 09-18-2015
Is this a homework assignment?

Homework and coursework questions can only be posted in this forum under special homework rules.

If this is homework, please repost in the Homework and Coursework Forum. If not, please explain why you are trying to do this.

Hi disedorgue,
I am hiding your response until we get an answer to the homework question.
# 4  
Old 09-18-2015
Hi Don,

This is not an either homework or coursework assignment. I am playing with sed commands and so want to know that how we can read the lines from the bottom using sed.

Please let me know if still I need to post my question to homework forum?


Thanks
# 5  
Old 09-18-2015
Not sure if this can be done with sed alone. Try
Code:
LN=4
tac file | sed ${LN}a"NEW LINE" | tac
Old Line
Old Line
NEW LINE
Old Line
Old Line
Old Line
Old Line

This User Gave Thanks to RudiC For This Post:
wridler
# 6  
Old 09-18-2015
Thanks Rudi it worked..
# 7  
Old 09-18-2015
If you're trying to learn how to use sed, you should also learn to recognize things that sed was not designed to do (like counting lines backwards from the end of a file). A tool like ed or ex could handle an assignment like this without needing to invoke tac twice to get data in a format that sed can handle... For instance, if you want to update the contents of the file:
Code:
#!/bin/ksh
LN=4
IP=$((LN - 1))
ed -s file.txt <<-EOF
        .-${IP}i
	.
	w
	q
EOF

or if you just want to print the updated contents (so you can redirect the output to a different file or just view the update):
Code:
#!/bin/ksh
LN=4
IP=$((LN - 1))
ed -s file.txt <<-EOF
        .-${IP}i
NEW LINE!
        .
        1,$ p
        Q
EOF

This User Gave Thanks to Don Cragun For This Post:
disedorgue
 
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