Test if the first character is a number using awk

Question

How do I check if the first character of a string is a number using awk. I have tried below but i keep getting syntax error.

awk ' { if (substr($1,1,1) == [0-9] ) print $0 }' da.txt

Answer 1

I will suggest to use @hek2mgl solution. I have pointed out some of the problems.

Problems:

1. You should use regex inside /..regex../.
2. Use ~ instead of ==.

Valid:

awk '{ if (substr($1,1,1) ~ /^[0-9]/ ) print $0 }' file.txt