How do I limit the number of results returned from grep?
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I would like to say 10 lines max from grep.
I don't want my computer to work hard. I want it to stop after 10 results found by grep. Is it possible?
Linux Solutions
Solution 1 - Linux
The -m
option is probably what you're looking for:
grep -m 10 PATTERN [FILE]
From man grep
:
-m NUM, --max-count=NUM
Stop reading a file after NUM matching lines. If the input is
standard input from a regular file, and NUM matching lines are
output, grep ensures that the standard input is positioned to
just after the last matching line before exiting, regardless of
the presence of trailing context lines. This enables a calling
process to resume a search.
Note: grep stops reading the file once the specified number of matches have been found!
Solution 2 - Linux
Another option is just using head:
grep ...parameters... yourfile | head
This won't require searching the entire file - it will stop when the first ten matching lines are found. Another advantage with this approach is that will return no more than 10 lines even if you are using grep with the -o option.
For example if the file contains the following lines:
112233
223344
123123
Then this is the difference in the output:
$ grep -o '1.' yourfile | head -n2 11 12$ grep -m2 -o '1.' 11 12 12
Using head
returns only 2 results as desired, whereas -m2 returns 3.
Solution 3 - Linux
Awk approach:
awk '/pattern/{print; count++; if (count==10) exit}' file
Solution 4 - Linux
For 2 use cases:
- I only want n overall results, not n results per file, the
grep -m 2
is per file max occurrence. - I often use
git grep
which doesn't take-m
A good alternative in these scenarios is grep | sed 2q
to grep first 2 occurrences across all files. sed documentation: https://www.gnu.org/software/sed/manual/sed.html
Solution 5 - Linux
Using tail:
#dmesg
...
...
...
[132059.017752] cfg80211: (57240000 KHz - 65880000 KHz @ 2160000 KHz), (N/A, 4000 mBm)
[132116.566238] cfg80211: Calling CRDA to update world regulatory domain
[132116.568939] cfg80211: World regulatory domain updated:
[132116.568942] cfg80211: (start_freq - end_freq @ bandwidth), (max_antenna_gain, max_eirp)
[132116.568944] cfg80211: (2402000 KHz - 2472000 KHz @ 40000 KHz), (300 mBi, 2000 mBm)
[132116.568945] cfg80211: (2457000 KHz - 2482000 KHz @ 40000 KHz), (300 mBi, 2000 mBm)
[132116.568947] cfg80211: (2474000 KHz - 2494000 KHz @ 20000 KHz), (300 mBi, 2000 mBm)
[132116.568948] cfg80211: (5170000 KHz - 5250000 KHz @ 40000 KHz), (300 mBi, 2000 mBm)
[132116.568949] cfg80211: (5735000 KHz - 5835000 KHz @ 40000 KHz), (300 mBi, 2000 mBm)
[132120.288218] cfg80211: Calling CRDA for country: GB
[132120.291143] cfg80211: Regulatory domain changed to country: GB
[132120.291146] cfg80211: (start_freq - end_freq @ bandwidth), (max_antenna_gain, max_eirp)
[132120.291148] cfg80211: (2402000 KHz - 2482000 KHz @ 40000 KHz), (N/A, 2000 mBm)
[132120.291150] cfg80211: (5170000 KHz - 5250000 KHz @ 40000 KHz), (N/A, 2000 mBm)
[132120.291152] cfg80211: (5250000 KHz - 5330000 KHz @ 40000 KHz), (N/A, 2000 mBm)
[132120.291153] cfg80211: (5490000 KHz - 5710000 KHz @ 40000 KHz), (N/A, 2700 mBm)
[132120.291155] cfg80211: (57240000 KHz - 65880000 KHz @ 2160000 KHz), (N/A, 4000 mBm)
alex@ubuntu:~/bugs/navencrypt/dev-tools$ dmesg | grep cfg8021 | head 2
head: cannot open ‘2’ for reading: No such file or directory
alex@ubuntu:~/bugs/navencrypt/dev-tools$ dmesg | grep cfg8021 | tail -2
[132120.291153] cfg80211: (5490000 KHz - 5710000 KHz @ 40000 KHz), (N/A, 2700 mBm)
[132120.291155] cfg80211: (57240000 KHz - 65880000 KHz @ 2160000 KHz), (N/A, 4000 mBm)
alex@ubuntu:~/bugs/navencrypt/dev-tools$ dmesg | grep cfg8021 | tail -5
[132120.291148] cfg80211: (2402000 KHz - 2482000 KHz @ 40000 KHz), (N/A, 2000 mBm)
[132120.291150] cfg80211: (5170000 KHz - 5250000 KHz @ 40000 KHz), (N/A, 2000 mBm)
[132120.291152] cfg80211: (5250000 KHz - 5330000 KHz @ 40000 KHz), (N/A, 2000 mBm)
[132120.291153] cfg80211: (5490000 KHz - 5710000 KHz @ 40000 KHz), (N/A, 2700 mBm)
[132120.291155] cfg80211: (57240000 KHz - 65880000 KHz @ 2160000 KHz), (N/A, 4000 mBm)
alex@ubuntu:~/bugs/navencrypt/dev-tools$ dmesg | grep cfg8021 | tail -6
[132120.291146] cfg80211: (start_freq - end_freq @ bandwidth), (max_antenna_gain, max_eirp)
[132120.291148] cfg80211: (2402000 KHz - 2482000 KHz @ 40000 KHz), (N/A, 2000 mBm)
[132120.291150] cfg80211: (5170000 KHz - 5250000 KHz @ 40000 KHz), (N/A, 2000 mBm)
[132120.291152] cfg80211: (5250000 KHz - 5330000 KHz @ 40000 KHz), (N/A, 2000 mBm)
[132120.291153] cfg80211: (5490000 KHz - 5710000 KHz @ 40000 KHz), (N/A, 2700 mBm)
[132120.291155] cfg80211: (57240000 KHz - 65880000 KHz @ 2160000 KHz), (N/A, 4000 mBm)
alex@ubuntu:~/bugs/navencrypt/dev-tools$