compare date

#!/bin/bash
# Usage: ./script 201701 201703
From=$(date -d $(sed 's/^\(....\)\(..\).*/\1-\2-01/' <<<$1) +%s)
To=$(date -d $(sed 's/^\(....\)\(..\).*/\1-\2-01/' <<<$2) +%s)
for f in test_*.tar.gz; do
  date=$(date -d $(sed 's/^test_\(....\)\(..\).*/\1-\2-01/' <<<$f) +%s)
  if (( From <= date && date <= To )); then
    echo $f
  fi
done