[SOLVED] trying to insert text in the last line of a file with sed command....

Sayan Acharjee · 10-04-2010, 03:25 AM

I want to insert the text "DB dept" in the last line of passwd file which looks like this right now

Quote:

newuser:x:717:717::/home/sacharje:/bin/bash

And I want it to be like this:

Quote:

newuser:x:717:717: DB dept:/home/sacharje:/bin/bash

I tried to do that with sed but failed, I'd like to know the proper syntex with sed to achieve this, kindly help.

Thanks in advance

druuna · 10-04-2010, 03:37 AM

Hi,

sed '$s/::/:DB dept:/' infile

The $ tells sed to only do this for the last line.

Hope this helps.

Sayan Acharjee · 10-04-2010, 03:48 AM

When I am using that command it shows that it worked but now when I open the file again I don't see the change. :|

ghostdog74 · 10-04-2010, 03:58 AM

Code:

awk -F":" '{print p}{p=$0}END{$5="DB dept"$5;print}' OFS=":" /etc/passwd > t && mv t /etc/passwd

make sure you are root.

Sayan Acharjee · 10-04-2010, 04:04 AM

Thanks, it worked

What changes I need to make to the command to do the same for a specific line, say line no. 23?

David the H. · 10-04-2010, 04:25 AM

Like most applications of this type, sed doesn't modify the file itself by default, but you can add the -i option to do so.

The basic format of a sed command is this:

sed [options] (-e)[address range][expression] (-e [address range][expression])

The address range tells sed which lines to operate on. It can be a single number for one line, or number1,number2 for a range of lines. There's also $ to mean the last line and a few more modifiers.

Code:

sed -i '$ s/a/b/g'   #changes all a's to b's on the last line of the file,
                     #modifying the original.

sed '5,7 d'  #deletes lines 5-7, but only in the screen output.

sed -n '5,7p' #prints only lines 5-7 from the file.

sed '10 a foobar' #adds "foobar" after line 10.

sed can do a lot more than most people realize.
Here are a few useful references:
http://www.grymoire.com/Unix/Sed.html
http://sed.sourceforge.net/sedfaq.html
http://sed.sourceforge.net/sed1line.txt