What unix command can we use to append some text to a specific line in a file?

Does anyone know of a series of unix commands that allows someone to append some text to the end of a specific line in a file?

eg

Line 1

Line 2

Line 3

Line 4

I wish to append the text ", extra information" to Line 3 so that the File will now look like this:

Line 1

Line 2

Line 3, extra information

Line 4

From stackoverflow

• Here is a version with portable sed (without -i option):

  sed '3s/$/Hello World/' myfile
  

  Note that myfile is not modified, so you can recover from possible mistakes.

  Joachim Sauer : superfluous use of cat! Oh noes!

  Johannes Weiß : sed -i '3s/$/Hello World/' myfile is better

  Paul Tomblin : This won't actually change "myfile".

  mouviciel : From the sed(1) man page of Mac OS X 10.5.6: "The -E, -a and -i options are non-standard FreeBSD extensions and may not be available on other operating systems." So for maximum portability, I didn't suggest inline modifications.

  Paul Tomblin : If you don't want to use -i, then at least explain why your answer doesn't do what the question asks.

  Paul Tomblin : Personally, I would write it as "sed ... myfile > myfile.$$ && mv myfile.$$ myfile"

• sed -e "s/^Line 3/\0, extra info/" -i text.txt
  

  Ryan Graham : I think he means by line number, not line content.

  Joachim Sauer : I got that ... doesn't matter, now he knows both ways ;-)

• in awk it's:

  awk '{s=$0; if( NR==3 ){ s=s ", Extra Information" } print s;}' myfile > newfile
  

  proper sed version:

  sed -e '3s/$/, Extra Information/' -i myfile
  

• awk 'NR == 3 { print $0 ", extra information" } NR != 3' myfile
  

  The part before the braces is the condition: If we are in line 3, we append some text. If braces are omitted, the default action is to just print out $0. Redirect to a new file or pipe to another program as appropriate. You cannot redirect to the same file you are just reading. A common workaround is to redirect to a new file, and then move over if the command was successful:

  somecommand > oldfile.tmp && mv oldfile.tmp oldfile
  

  yesraaj : have a look at qn http://stackoverflow.com/questions/598143/explain-about-linkagesexternal-internal-in-c/598180#598180

  Johannes Schaub - litb : i've nothing to add to his answer :) i like the linked blog entry about linkage too.

• Perl:

  perl -p -e's{\n}{, extra information\n} if $. ==3' myfile
  

  $. is the line number

• If you want the extra information to be appended to just one line, any of the sed/awk one-liners will do.

  If you want to append something to (almost) every line in the file, you should create a second file with the extra information for each line and use paste:

  $ cat myfile
  line 1
  line 2
  line 3
  line 4
  $ cat extra 
  something
  
  something else
  $ paste myfile extra
  line 1  something
  line 2
  line 3  something else
  line 4