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Two numbers in brackets
If there are two numbers, n and m, in brackets, then it means that the preceded item must be matched at least n times but not more than m times. The values of n and m must be non-negative and smaller than 255. For example, to match the occurrence of a minimum of 2 numbers and a maximum of 6 numbers between a and b in a line, we can use the following regular expression:
$ awk '/a[0-9]{2,6}b/' interval_regex.txt
The output on execution of the preceding code is as follows:
a12b
a123b
a1234b
a12345b
a111b
a111111b
In interval expression, the preceding regular expression should be a single-character regular expression, or if it is a string, it must be enclosed in a bracketed regular expression. For example:
$ awk '/(ab){2,3}/' interval_regex.txt
The output on execution of the preceding code is as follows:
cababababt
cababt
A summary of interval expressions is as follows:
Pattern |
Matches |
A{3}B |
Matches the line with AAAB |
A{3,}B |
Matches AAAB, AAAAB,or AAAAAB, and so on |
A{3,5}B |
Matches AAAB, AAAAB, or AAAAAB |
{4,8} |
Matches any line with {4,8} |
X(ab){2}Z |
Matches any XababZ |