Question

I have an example of a regular expression:

seq 20 | awk 'NR!~/^2$|^12$|^15$/'

The same, but with the chain expression:

seq 20 | awk 'NR != "2" && NR != "12" && NR != "15"'

Is it possible to write shorter string expression?

seq 20 | awk 'NR != "2" | "12" | "15" '

Thank you for the explanation.

Answer 1

Not to my knowledge. And like you have hinted at, you will need to use a regular expression if you would like to perform equality testing (or inequality testing, in this case) in this way.

If you have multiple values to ignore, consider using an array in the BEGIN block. This will make the expression shorter (i.e. the expression is now simply: !(NR in array)) when awk iterates through each line:

seq 20 | awk 'BEGIN { array[2]++; array[12]++; array[15]++ } !(NR in array)'

Results:

1
3
4
5
6
7
8
9
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11
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16
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20

If you there is some sort of pattern to the lines your trying to ignore, consider using a for loop in the BEGIN block:

seq 20 | awk 'BEGIN { for (i=1; i<=15; i++) array[i]++ } !(NR in array)'

16
17
18
19
20