A regular expression for finding numbers and spaces in a specific configuration

Question

A regular expression is required, which must find a sequence of 12 numbers, between which there can be no more than 2 spaces (not newlines) inside. Here are examples:

Example 1:3345624 90812
Example 2:908 7865123 23
Example 3:908765312334
Example 4:90878903556 1
Example 5:67555123452  5

An example of an invalid pattern is /[0-9|\s]{12,14}/, it allows trailing spaces, single spaces, newlines or alternating spaces and numbers.

Answer 1

I would do [\d ]{12,14} and then in the calling code see if result has 12 numbers or 2 spaces. Otherwise brute-force generate a regex along these lines:

\d{12}|              # 1 number

\d{1} {1,2}\d{11}|   # 2 numbers
...
\d{11} {1,2}\d{1}|

\d{1} \d{1} \d{10}|  # 3 numbers
...
\d{10} \d{1} \d{1}

Here's a suitable bash script to generate the regex:

sep='|'
#sep=$'\n'
printf '\d{12}%s' "$sep"
for((i=1; i<=11; i++))
do 
    printf '\d{%d} {1,2}\d{%d}%s' $i $((12-i)) "$sep"
done
for((i=1; i<=10; i++))
do
    for((j=1; i+j<=11; j++))
    do
        [ $i -eq 10 -a $j -eq  1 ] && sep=$'\n'
        printf '\d{%d} \d{%d} \d{%d}%s' $i $j $((12-i-j)) "$sep"
   done
done

and example run:

\d{12}|\d{1} {1,2}\d{11}|\d{2} {1,2}\d{10}|\d{3} {1,2}\d{9}|\d{4} {1,2}\d{8}|\d{5} {1,2}\d{7}|\d{6} {1,2}\d{6}|\d{7} {1,2}\d{5}|\d{8} {1,2}\d{4}|\d{9} {1,2}\d{3}|\d{10} {1,2}\d{2}|\d{11} {1,2}\d{1}|\d{1} \d{1} \d{10}|\d{1} \d{2} \d{9}|\d{1} \d{3} \d{8}|\d{1} \d{4} \d{7}|\d{1} \d{5} \d{6}|\d{1} \d{6} \d{5}|\d{1} \d{7} \d{4}|\d{1} \d{8} \d{3}|\d{1} \d{9} \d{2}|\d{1} \d{10} \d{1}|\d{2} \d{1} \d{9}|\d{2} \d{2} \d{8}|\d{2} \d{3} \d{7}|\d{2} \d{4} \d{6}|\d{2} \d{5} \d{5}|\d{2} \d{6} \d{4}|\d{2} \d{7} \d{3}|\d{2} \d{8} \d{2}|\d{2} \d{9} \d{1}|\d{3} \d{1} \d{8}|\d{3} \d{2} \d{7}|\d{3} \d{3} \d{6}|\d{3} \d{4} \d{5}|\d{3} \d{5} \d{4}|\d{3} \d{6} \d{3}|\d{3} \d{7} \d{2}|\d{3} \d{8} \d{1}|\d{4} \d{1} \d{7}|\d{4} \d{2} \d{6}|\d{4} \d{3} \d{5}|\d{4} \d{4} \d{4}|\d{4} \d{5} \d{3}|\d{4} \d{6} \d{2}|\d{4} \d{7} \d{1}|\d{5} \d{1} \d{6}|\d{5} \d{2} \d{5}|\d{5} \d{3} \d{4}|\d{5} \d{4} \d{3}|\d{5} \d{5} \d{2}|\d{5} \d{6} \d{1}|\d{6} \d{1} \d{5}|\d{6} \d{2} \d{4}|\d{6} \d{3} \d{3}|\d{6} \d{4} \d{2}|\d{6} \d{5} \d{1}|\d{7} \d{1} \d{4}|\d{7} \d{2} \d{3}|\d{7} \d{3} \d{2}|\d{7} \d{4} \d{1}|\d{8} \d{1} \d{3}|\d{8} \d{2} \d{2}|\d{8} \d{3} \d{1}|\d{9} \d{1} \d{2}|\d{9} \d{2} \d{1}|\d{10} \d{1} \d{1}