sed append line on 1 occurrence only

Question

Have this file

ServerName *
ServerAlias *
ServerAlias *

<Directory>

I want to append a new line after the first occurrence of ServerAlias with the text S2. I have tried the following

sed '/ServerAlias/ a\S2\' foo

But this appends after all the occurrences.

My final result should be

ServerName *
ServerAlias *
S2
ServerAlias *

<Directory>

ДМИТРИЙ МАЛИКОВ · Accepted Answer · 2011-10-26T19:04:24.077

5

Actually, it's not sed, but maybe awk can help you.

$> cat ./file
ServerName *
ServerAlias *
ServerAlias *

<Directory>

$> awk '{print} /^ServerAlias/ && !n {print "S2"; n++}' ./file
ServerName *
ServerAlias *
S2
ServerAlias *

<Directory>

UPD: mistake is fixed now, thanks glenn_jackman

edited Oct 26 '11 at 19:04

answered Oct 26 '11 at 18:53

ДМИТРИЙ МАЛИКОВ

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1

You'd probably need to anchor the regexp to avoid matching "ServerAlias" in comments. – glenn jackman Oct 26 '11 at 18:57
1

To avoid printing the matched line twice, use: `awk '{print} /^ServerAlias/ && !n {print "S2"; n++}' file` – glenn jackman Oct 26 '11 at 18:58
Fixed. Thanks for great observation. – ДМИТРИЙ МАЛИКОВ Oct 26 '11 at 19:06

cmbuckley · Answer 2 · 2013-03-25T12:25:40.927

2

The awk solution above is best, but if you really want to do it in (GNU) sed then the following does the trick:

sed '0,/^ServerAlias.\+/s//\0\nS2/' file

Credit goes to the sed FAQ.

edited Mar 25 '13 at 12:25

answered Oct 26 '11 at 19:26

cmbuckley

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It was some buggy if I repeated the command multiple times. Probably, it depends from OS lindendings. Instead, I used ServerName as a target, to add a ServerAlias after. – Fedir RYKHTIK Mar 25 '13 at 10:30
Related to the potential line ending issue: http://stackoverflow.com/questions/6111679/insert-linefeed-in-sed – cmbuckley Mar 25 '13 at 12:21

sed append line on 1 occurrence only

2 Answers2