How to write If conditions in regex? - regex

Question

I am trying to capture the amount from the following string:
Delivery Charge $2
Promo - (FIRST) ($4)
$7
New Coins earned $5
Issued on behalf of
.......................
The line "New Coins earned $5" might not be present sometime. I am willing to capture the Amount paid which is "7" in this case. I tried with \.?\s*\n*([\d.,]+)\s*\n*Issued\s*\n*on but this will only capture the amount if "New Coins earned $5" is not present in the document. I read about if else conditions and positive-lookahead. However, couldn't make this working. Any suggestions on how to capture?

Answer 1

Since the value you need is always preceded with $ on a separate line you may use
\$(\d[\d,.]*)[\n\r]+(?:.*[\r\n]+){0,2}Issued\s+on\b
The value you need is in Group 1.
Details
\$ - a $ char
(\d[\d,.]*) - Group 1: a digit followed with any 0+ digits, , or . chars
[\n\r]+ - 1 or more CR or LF symbols
(?:.*[\r\n]+){0,2} - 0, 1 or 2 repetitions of 0+ chars other than linebreak chars followed with 1+ LF/CR symbols
Issued\s+on\b - Issued, 1+ whitespaces, on as a whole word (as \b is a word boundary).
See the regex demo.
Python demo:
import re
rx = r"\$(\d[\d,.]*)[\n\r]+(?:.*[\r\n]+){0,2}Issued\s+on\b"
s = "Delivery Charge $2\nPromo - (FIRST) ($4)\n$1,000.55\nNew Coins earned $5\nIssued on behalf of ......................."
match = re.search(rx, s, re.M)
if match:
print(match.group(1)) # -> 1,000.55

Answer 2

You can do it like (?(?=regex)then|else), but notice that (?=) is lookahead and have zero length, so your then condition must match expression in brackets too.
You also can make more complex expressions in a way
(?(?=condition)(then1|then2|then3)|(else1|else2|else3))
Where then1, then2, then3 sorted in descending priority order, because first matching "then" condition will skip all others.
You can look for more info here