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# Checking if field contains numbers

Posted on 2000-04-19
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Hi!

How can I tell if \$FORM{count} only contains numbers, therefore no letters etc.

Graeme Sandwell
graeme@officedevil.co.uk
0
Question by:graemesandwell
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LVL 16

Accepted Solution

maneshr earned 100 total points
ID: 2730839
You want to check whether a string represents a valid number. This is a common problem when validating input, as in a CGI script.

This problem gets to the heart of what we mean by a number. Even things that sound simple, like integer, make you think hard about what you will accept ("Is a leading + for positive numbers optional, mandatory, or forbidden?").

You must decide what you will and will not accept. Then, construct a regular expression to match those things alone. Here are some precooked solutions  for most common cases.

## Sample value.
\$FORM{count}="1298";

## Eliminate any leading and trailing spaces from the variable
\$FORM{count}=~ s/^\s+//;
\$FORM{count}=~ s/\s+\$//;

## Now check...
if (\$FORM{count}!~ /^\d+\$/){ # rejects -3
print "not a natural number\n";
}

if (\$FORM{count}!~ /^-?\d+\$/){ ## rejects +3
print "not an integer\n";
}

if (\$FORM{count}!~ /^[+-]?\d+\$/){
print "not an integer\n";
}

if (\$FORM{count}!~ /^-?\d+\.?\d*\$/){ ## rejects .2
print "not a decimal number\n";
}

if (\$FORM{count}!~ /^-?(?:\d+(?:\.\d*)?|\.\d+)\$/){
print "not a decimal number\n";
}
0

LVL 84

Expert Comment

ID: 2731686
perldoc -q "How do I determine whether a scalar is a number/whole/integer/float"
0

Author Comment

ID: 2737606
Thanks for all the time you put into your answer!  I was looking for a number > 0.

Thanks again!

Graeme Sandwell
0

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