How can I filter the output by the number of characters in a column?

Question

linux

Good afternoon.
I am writing a script and needed to do the following. There is a file like this:
102 xxxxx xxxxxxxxxxx
150 xxxxx xxxxxxxxxxx
3000 xxxxx xxxxxxxxxxx
3600 xxxxx xxxxxxxxxxx
In general, the first columns can be 3-digit numbers or 4-ex. Here's how I can display only those lines in which there are 4 digits in the first column?

Answer 1

egrep '^[0-9]{4}' /your/file/is/here

Answer 2

cat file | grep '^....'

Answer 3

The dumbest way is to compare the first column with 1000 in a loop or, if options with leading zeros are possible, count the number of characters (see ${#VAR}).