Replace line after match

Question

Given this file

$ cat foo.txt
AAA
111
BBB
222
CCC
333

I would like to replace the first line after BBB with 999. I came up with this command

awk '/BBB/ {f=1; print; next} f {$1=999; f=0} 1' foo.txt

but I am curious to any shorter commands with either awk or sed.

Just remember that brevity isn't itself a desirable quality of software, conciseness (i.e. brevity with clarity) is. — Ed Morton, Dec 09 '13 at 19:41

score 9 · Accepted Answer · edited Nov 26 '19 at 03:53

9

This might work for you (GNU sed)

sed '/BBB/!b;n;c999' file

If a line contains BBB, print that line and then change the following line to 999.

!b negates the previous address (regexp) and breaks out of any processing, ending the sed commands, n prints the current line and then reads the next into the pattern space, c changes the current line to the string following the command.

edited Nov 26 '19 at 03:53

miken32

42,008
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answered Dec 09 '13 at 12:22

potong

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Jotne · Answer 2 · 2013-12-09T06:56:43.587

6

This is some shorter:

awk 'f{$0="999";f=0}/BBB/{f=1}1' file

f {$0="999";f=0} if f is true, set line to 999 and f to 0
/BBB/ {f=1} if pattern match set f to 1
1 print all lines, since 1 is always true.

edited Dec 09 '13 at 06:56

answered Dec 09 '13 at 06:50

Jotne

40,548
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`1 print all lines, since 1 is always true`. In fact it is a bit longer "1 prints all lines, since it is evaluated as true and the default action for "true" in `awk` is to `{print $0}`". Also, +1, I came up with the same solution when trying to squeeze the one-liner. – fedorqui Dec 09 '13 at 09:18

score 5 · Answer 3 · edited Dec 09 '13 at 12:13

5

can use sed also, it's shorter

sed '/BBB/{n;s/.*/999/}'

edited Dec 09 '13 at 12:13

Zombo

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answered Dec 09 '13 at 07:19

ray

4,109
1
17
12

999/;}', missing the ; for a posix compliant ;-) – NeronLeVelu Dec 09 '13 at 07:48
only thing I could get to work. – Arkham Angel Nov 02 '22 at 04:05

score 3 · Answer 4 · answered Dec 09 '13 at 19:39

3

$ awk '{print (f?999:$0); f=0} /BBB/{f=1}' file    
AAA
111
BBB
999
CCC
333

answered Dec 09 '13 at 19:39

Ed Morton

188,023
17
78
185

Vijay · Answer 5 · 2013-12-09T06:56:59.363

2

awk '/BBB/{print;getline;$0="999"}1' your_file

edited Dec 09 '13 at 06:56

answered Dec 09 '13 at 06:50

Vijay

65,327
90
227
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score -1 · Answer 6 · answered Dec 30 '13 at 01:20

-1

sed 's/\(BBB\)/\1\
999/'

works on mac

answered Dec 30 '13 at 01:20

toph

190
1
4

Replace line after match

6 Answers6

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