使用正则表达式提取Perl中的前两个单词

Question

I want to create extract the first two words from a sentence using a Perl function in PostgreSQL. In PostgreSQL, I can do this with:

text = "I am trying to make this work";

Select substring(text from '(^\w+-\w+|^\w+(\s+)?(!|,|\&|'')?(\s+)?\w+)');

It would return "I Am"

I tried to build a Perl function in Postgresql that does the same thing.

CREATE OR REPLACE FUNCTION extract_first_two (text)
    RETURNS text AS 
    $$
    my $my_text = $_[0];
    my $temp;

    $pattern = '^\w+-\w+|^\w+(\s+)?(!|,|\&|'')?(\s+)?\w+)';
    my $regex = qr/$pattern/;
    if ($my_text=~ $regex) {
    $temp = $1;
    }

    return $temp;
    $$ LANGUAGE plperl;

But I receive a syntax error near the regular expression. I am not sure what I am doing wrong.

Answer 1

Extracting words is none trivial even in English. Take the following contrived example using Locale::CLDR

use 'Locale::CLDR';
my $locale = Locale::CLDR->new('en');
my @words = $locale->split_words('adf543. 123.25');

@words now contains

• adf543
• .
• 123.25

Note that the full stop after adf543 is split into a separate word but the one between 123 and 25 is kept as part of the number 123.25 even though the '.' is the same character

If gets worse when you look at non English languages and much worse when you use non Latin scripts.

You need to precisely define what you think a word is otherwise the following French gets split incorrectly.

Je avais dit «Elle a dit «Il a dit «Ni» il ya trois secondes»»

Answer 2

The parentheses are mismatched in our regex pattern. It has three opening parentheses and four closing ones.

Also, you have two single quotes in the middle of a singly-quoted string, so

'^\w+-\w+|^\w+(\s+)?(!|,|\&|'')?(\s+)?\w+)'

is parsed as two separate strings

'^\w+-\w+|^\w+(\s+)?(!|,|\&|'')?(\s+)?\w+)'

and

'^\w+-\w+|^\w+(\s+)?(!|,|\&|'
')?(\s+)?\w+)'

But I can't suggest how to fix it as I don't understand your intention.

Did you mean a double quote perhaps? In which case (!|,|\\&|")? can be written as [!,&"]?

---

Update

At a rough guess I think you want this

my $regex = qr{ ^ \w++ \s* [-!,&"]* \s* \w+ }x;
$temp = $1 if $my_text=~ /($regex)/;

but I can't be sure. If you describe what you're looking for in English then I can help you better. For instance, it's unclear why you don't have question marks, full stops, and semicolons in the list of intervening punctuation.