create a PCRE expression that matches exactly the strings described. strings that have exactly 3 vowels in any position

vivian phung 0
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the vowels do not have to appear consecutively. The string bonfire should match, but beak and yearbook should not.

I tried using

grep -P '([aeiouy][aeiouy]*){3}'

but it only seems to work when the vowels are consecutive.

grep awk
4 Answers

This job can be done easily using awk without using any regex. Just set field separator to one of the vowels and then make sure we have 4 fields:

awk -F '[aeiouy]' 'NF == 4' file

PS: y is not really a vowel but included because of your shown example.

anubhava0

Use [^aeiouy] to match non-vowels. Put a sequence of these around each vowel pattern.

grep -x '[^aeiouy]*[aeiouy][^aeiouy]*[aeiouy][^aeiouy]*[aeiouy][^aeiouy]*' filename

Use the -x option to match the whole line, or anchor the regexp with ^ and $.

You don't need PCRE, this only uses traditional regexp patterns.

Barmar0

You don't need -P for Perl-compatible regular expressions.

If you want to match exactly 3 vowels using grep, you can use anchors and match 3 vowels surrounded by optional repetitions of the negated character class [^aeiouy]* matching any character except the vowels.

grep '^[^aeiouy]*\([aeiouy][^aeiouy]*\)\{3\}$' file

Or with -E

grep -E '^[^aeiouy]*([aeiouy][^aeiouy]*){3}$' file

If you want at least 3 vowels:

grep -E '([aeiouy][^aeiouy]*){2}[aeiouy]' file
The fourth bird0

Using any awk:

$ echo 'bonfire' | awk 'gsub(/[aeiouy]/,"&")==3'
bonfire
$ echo 'beak' | awk 'gsub(/[aeiouy]/,"&")==3'
$ echo 'yearbook' | awk 'gsub(/[aeiouy]/,"&")==3'
$
Ed Morton0
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