validation image name for docker agent

validate.sh

#!/bin/sh

PATTERN="^([a-z0-9]+([._-]{0,1}[a-z0-9])*\/)*[a-zA-Z0-9]+([._-]{0,1}[a-z0-9])*(:[A-Za-z0-9][A-Za-z0-9.-]*){0,1}$"

for input in \
  i \
  image \
  i:t \
  i:t::: \
  image:t \
  i:tag \
  r/i \
  r/i: \
  r/i:t \
  repo/i \
  repo/i:t \
  repo/i:t: \
  repo/i:t:t2 \
  repo_/i \
  repo_test/i \
  repo__test/i \
  repo.s-i_tory/i; do
    printf "input: %-16s ---> " $input
    echo "$input" | egrep -q -s "${PATTERN}"
    [ $? -eq 0 ] && echo "pass (0)" || echo "fail (1)"
done