regex meaning

[hashin_p]

Hi, Could you detail on the regular expression $str =~ s/^0+(?=\d)// What is the meaning of the above? Thanks, Hashin

[prasadbabu]

Replacing the number starting with one or more zeros and followed by a number with none. Here (?=\d), is positive look ahead which has zero width assertion. So it ll replace only the zeroes and not the following number.

Take a look at perlre and YAPE::Regex::Explain

For example:

$str = '004asdfsa'; #string starting with zero and followed by numbers

$str =~ s/^0+(?=\d)//;

print $str;

Output:
--------
4asdfsa

$str = 'a004asdfsa'; #not starting with zero

$str =~ s/^0+(?=\d)//;

print $str;

Output:
--------
a004asdfsa

$str = '0a4sdfsa'; #no number followed by zero

$str =~ s/^0+(?=\d)// ;

print $str;

Output:
--------
0a4sdfsa

[bart]

(I agree with what you say, but... I think a little simplification may be in order.)

The reason for the lookahead (?=\d) is so it wouldn't replace a string "0000" with "", but with "0", by requiring at least one remaining digit.

So the purpose is to strip leading zeros from strings that look like numbers, but leave a significant "0".

[hashin_p]

Thank you very much..

[oha]

• ^ matches the start of the string
• 0+ matches one or more zeroes
• (?= followed by
• \d a number

  it will substitute those zeroes with nothing. so it removes leading zeroes iff they are followed by a number

  Oha