Here's a couple of guesses at what you want:

/\d{0,3}/
matches:
"123"
"  123"
"123  "
"  123  "
"foo123bar"
doesn't match:
"1 2 3"

/^\s*\d{0,3}\s*$/
matches:
"123"
"  123"
"123  "
"  123  "
doesn't match:
"foo123bar"
"1 2 3"

/^\s*(?:\d\s*){0,3}$/
matches:
"123"
"  123"
"123  "
"  123  "
" 1 2 3 "
doesn't match:
"foo123bar"

Thanks ikegami. /\d{0,3}/ works ok if there are three digits somewhere in the field.

It doesn't match:
"1 "
"12 "
" 1"
" "

To attempt to grab any digits in the field, or only white space, I have tried /\d{0,3}|\W{3}/.

Haven't found any examples on the Web or the Perl reference that might assist as yet. Any suggestions?

Hi ikegami,

Figured it out.

/\d{3}|\d\s\s|\d\d\s|\W{3}/

Thanks for your help.

hum, it does matches all of those

print(   "1  " =~ /\d{0,3}/   ?"match":"no match", $/);
print(   "12 " =~ /\d{0,3}/   ?"match":"no match", $/);
print(   "  1" =~ /\d{0,3}/   ?"match":"no match", $/);
print(   "   " =~ /\d{0,3}/   ?"match":"no match", $/);
[download]

Now, if you want the regexp to completely match exactly three characters, consiting of 0+ digits padded with spaces on either side, that's much more complicated.

We can write it out the long way:
/^(?:   |  \d| \d\d|\d\d\d|\d  |\d\d |\d  )$/
This doesn't compress well.

/^[ \d]{3}$/
will match them all, but it will also match "1 2".

/^(?: [ \d]{2}|[ \d]{2} |\d{3})$/ will work.

Anything else I can think of invovles potentially matching more than three characters (/^\s*\d{0,3}\s*$/) or involves more than a regexp.

If the spaces can only be leading spaces, then the long form would be:
/^(?:   |  \d| \d\d|\d\d\d)$/
which doesn't really simplify.

btw, you should be using \D if you mean non-digit, or \S if you mean non-whitespace. \W doesn't appear to be appropriate here.

It sounds like you might want /^[\d\s]{0,3}$/, which works if the length is exactly 3 characters, each a space or a digit. Another approach might be to use more than just a pattern, if (length == 3 && /^\d*\s*$/), for instance, if you want the blanks to follow all the digits. Or if you want to extract the digits part and validate, you could do something like

if (length != 3 || !/^(\d*)\s*/){
  die "invalid data";
} else {
  print "your number without spaces is '$1'\n";
}
[download]

while (<DATA>) {
    print $1."\n" if /^\D*(\d{0,3})\D*$/;
}

__DATA__
123
  123
123  
  123  
1 2 3
1 
12 
 1
[download]