Get first n matches with awk

Question

I am using dbus-monitor command to see every Dbus signal, the command is an infinite loop, so I am using awk with it to grep for a specific pattern.

I can get the first match and exit using:

dbus-monitor --system | awk '/<pattern>/ {print $2; exit}'

But, my system is going to a list of states for example x1 -> x2 -> x3

I want to use awk to get the first 3 signals of a given pattern and print them.

For example, when I start the system, x1 is sent and I can detect it with the first awk command, but when I run it again, I get x3, because x2 is already sent I did not catch it in time.

How can I change awk to use for example a counter and get me the first n matches?

Thanks.

[edit] your question to include a [mcve] with concise, testable sample input and expected output so we can help you. Also, replace the word "pattern" throughout your question with whatever you really mean - partial regexp match, full line regexp, full word regexp, partial string, full word string, full line string, etc. See [how-do-i-find-the-text-that-matches-a-pattern](https://stackoverflow.com/questions/65621325/how-do-i-find-the-text-that-matches-a-pattern). — Ed Morton, Jul 21 '22 at 13:01

score 0 · Accepted Answer · answered Jul 21 '22 at 12:39

0

Increment a counter variable, then test it to decide whether to exit.

dbus-monitor --system | awk '/<pattern>/ {counter++; print $2; if (counter == 3) exit}'

answered Jul 21 '22 at 12:39

Barmar

741,623
53
500
612

I tried it with `4` but it did not exit, it prints 4 elements and still keeps waiting. – Talel BELHADJSALEM Jul 21 '22 at 12:50
I just tested this with a log file on our server and it worked. – Barmar Jul 21 '22 at 13:01
1

To save repeating the variable name: `{print $2; if (++counter == 3) exit}` – Ed Morton Jul 21 '22 at 13:38

score 0 · Answer 2 · answered Jul 21 '22 at 13:05

you can decrement it down to zero just as easily

jot 1000 |

{m,g}awk '__<NF { exit } __>(__-=_^($_ % 181))' FS='^$' __=3

181
362
543

The left side portion handles the exit when counter reaches zero, the right side portion handles the pattern you want it to match, plus keep tracking how many times you've printed so far.

here my criteria is simple - find multiples of the prime number 181

Get first n matches with awk

2 Answers2