Problems with preg_match - php

Question

I'm using preg_match as a way to validate inputs on a form. Specifically, I am trying to validate input of currency. Here is the function:
if (preg_match("/^\$(((\d{1,3},)+\d{3})|\d+)\.\d{2}$/i", $inString)) {
return True;
} else {
return False;
}
I can get this to work AT ALL. I keeps returning False regardless of what I feed it (including valid strings). I'm sure I'm doing something obviously wrong, but I can't see it. You know how it is...
Anyone have any suggestions?

Answer 1

Try something like this:
$inString = '1550.50';
if (preg_match("/\b\d{1,3}(?:,?\d{3})*(?:\.\d{2})?\b/", $inString)) {
echo "True";
} else {
echo "False";
}
explanation:
\b # word boundary assertion
\d{1,3} # 1-3 digits
(?: # followed by this group...
,? # an optional comma
\d{3} # exactly three digits
)* # ...any number of times
(?: # followed by this group...
\. # a literal dot
\d{2} # exactly two digits
)? # ...zero or one times
\b # word boundary assertion

Answer 2

The preg_match function already returns True or False depending on whether it matches, so there is no need to return True or False a second time.
This means you can directly echo the values of True or False:
$inString = "$12.50";
$price_regex = '~^\$(((\d{1,3},)+\d{3})|\d+)\.\d{2}$~';
echo preg_match($price_regex, $inString);
// echoes 1
You can also directly return these values:
return preg_match($price_regex, $inString);
You can perform a Boolean test:
if( preg_match($price_regex, $inString) ) { // take some action }
else { // take another action }
If what you want instead is to echo some value depending on whether there is a match, do this:
echo (preg_match($price_regex, $inString)) ? "**It Matches!**" : "Nah... No match." ;
Notes:
Changed the delimiter to ~ (more legible)
Removed the i flag (there are no letters, so it doesn't need to be case-insensitive)

Answer 3

Both answers given before this work, but here's an explanation of why the original preg_match pattern didn't work.
It's because the pattern is enclosed in double quotes. When PHP sees this, it treats whatever follows a $ sign as a variable name. If you need to include a literal $ sign inside a double quoted string, the dollar has to be preceded by a backslash.
so both of these patterns work:
'/^\$(((\d{1,3},)+\d{3})|\d+)\.\d{2}$/i'
"/^\\$(((\d{1,3},)+\d{3})|\d+)\.\d{2}\$/i"
Obviously, using single quotes is simpler in this case.