How to grep for contents after pattern?

Question

Given a file, for example:

potato: 1234
apple: 5678
potato: 5432
grape: 4567
banana: 5432
sushi: 56789

I\'d like to grep for all lines that

Answer 1

Modern BASH has support for regular expressions:

while read -r line; do
  if [[ $line =~ ^potato:\ ([0-9]+) ]]; then
    echo "${BASH_REMATCH[1]}"
  fi
done