Display only the n'th match of grep

Question

onefish
onechicken
twofish
twochicken
twocows
threechicken

What if I want to grep for lines containing "two", but I only want the 2nd match. So I want the result "twochicken".

John Zwinck · Answer 1 · 2013-02-28T14:29:42.053

37

grep -m2 "two" in-file.txt | tail -n1

Stop after the second match, then take the second line printed.

edited Feb 28 '13 at 14:29

answered Feb 28 '13 at 12:23

John Zwinck

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1

that does not exactly do what is expected. if there are more matches than two, it will output multiple lines... – poncha Feb 28 '13 at 12:34
2

The tail should be: `tail -n1`. – Thor Feb 28 '13 at 13:01
1

@poncha: really? The grep -m2 makes sure there are only two matches. I changed it anyway, though I think it was OK before. – John Zwinck Feb 28 '13 at 14:29

score 33 · Accepted Answer · answered Feb 28 '13 at 12:24

33

try this:

awk '/two/{i++}i==2' file

with your data:

kent$  echo "onefish
onechicken
twofish
twochicken
twocows
threechicken"|awk '/two/{i++}i==2'
twochicken

note: if your file is huge, do this:

awk '/two/{i++}i==2{print; exit}' file

answered Feb 28 '13 at 12:24

Kent

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the second option is superior regardless of filesize, no ? – poncha Feb 28 '13 at 12:27
what do you mean by 'line number' ? i meant that adding `{print; exit}` would be good idea for any input size... oh. that was option #3 actually ;) i counted wrong))) – poncha Feb 28 '13 at 12:35
1

is there a way to stop at nth occurrence of the word? I mean, if the "word" is repeated multiple times in a single line? – anishsane Feb 28 '13 at 14:56
@anishsane i think there is. – Kent Feb 28 '13 at 16:01
Is there a way to pass a the `search-pattern` and the no. of occurence `N` as a string – rambalachandran May 17 '16 at 14:05
@WanderingMind yes, you can define variables – Kent May 17 '16 at 19:02
Can you edit your answer to let me know how to pass a variable as search pattern – rambalachandran May 17 '16 at 19:03
1

`awk -v p="two" -v n="2" '$0~p{i++}i==n' file` @WanderingMind – Kent May 17 '16 at 19:06
Thank you for the reply. – rambalachandran May 17 '16 at 19:07
This is buggy -- if you remove `twocows` from the example, then it prints *both* `twocows` and `threechickens`, because `i` only iterates on lines that include "two" -- so if `i` reaches 2 on the last occurrence of the target string, then `i` remains 2 throughout the rest of the file, and every subsequent line is printed. (However, the "if your file is huge" addendum fixes this bug.) – DreadPirateShawn Jan 21 '18 at 07:33
@Kent can you please explain what does `{i++}i==2` do? – Manuel Jordan Jan 22 '22 at 15:21
1

@ManuelJordan `/two/{A} i==2 {B}` = `if($0~/two) do A; if(i==2) do B` – Kent Jan 22 '22 at 15:53

score 9 · Answer 3 · answered Jan 12 '19 at 00:02

grep and sed can be used to filter the line number.

testfile:

onefish
onechicken
twofish
twochicken
threechicken
twocows

Getting the desired line:

grep "two" testfile | sed -n 2p
prints "twochicken"

grep "two" testfile | sed -n 1p
prints "twofish"

score 2 · Answer 4 · answered Oct 20 '21 at 15:55

2

To use grep command for the n_th match, we can use the combination of head and tail commands like this:

grep two file.txt | head -n1 | tail -1

where n1 is the n_th match we need.

answered Oct 20 '21 at 15:55

Louis

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score 1 · Answer 5 · answered Feb 28 '13 at 15:04

1

If the word (here word==two) repeats multiple time in a single line, & you want to print that line, use below:

word=two
n=2
line=`grep -m$n $word -o -n MyFile | sed -n $n's/:.*//p'`
awk 'FNR=='$line'{print; exit}' MyFile

e.g. For below input:

onefish
onechicken
twotwofish
twochicken
twocows
threechicken

it will print twotwofish, instead of twochicken.

This may not be what user1787038 wants, but added to answer my own comment.

answered Feb 28 '13 at 15:04

anishsane

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`-m$n` in grep line is just for some optimization, not needed for functionality. – anishsane Feb 28 '13 at 15:05

score 1 · Answer 6 · answered Oct 24 '16 at 20:36

It should be noted that if the threechicken and twocows lines were swapped, aka:

onefish
onechicken
twofish
twochicken
threechicken
twocows

then Kent's first response (awk '/two/{i++}i==2' file) would yield the output:

twochicken
threechicken

because it takes another occurrence of the match to increment the counter. His last response: awk '/two/{i++}i==2{print; exit}' file avoids this issue.

Display only the n'th match of grep

6 Answers6

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