dotfiles/bin/version-compare

#!/usr/bin/env bash
set -euo pipefail

# Compare 2 version strings.
#
# Requires 2 parameters. Version strings are compared numerically, left to
# right, field by field.
#
# Prints 0 if versions are equal.
# Prints 1 if first > second.
# Prints -1 if first < second.

# Split strings on '.'.
IFS=.
[[ $# != 2 ]] && echo "Usage: ${0##*/} ver1 ver2" && exit 1
ver1=($1)
ver2=($2)
declare i fields

# Number of version fields to be compared = highest array count.
[[ ${#ver1[@]} > ${#ver2[@]} ]] && fields=${#ver1[@]} || fields=${#ver2[@]}

# Compare fields until a winner is found.
for (( i=0; i < $fields; i++ )); do
  # Use zero for missing fields e.g. when 1.2.3 vs 1.2, one more field needed.
  (( $i >= ${#ver1[@]} )) && ver1[i]=0
  (( $i >= ${#ver2[@]} )) && ver2[i]=0
  # Stop whenever a field value is larger than the other. Compared in base 10.
  (( 10#${ver1[i]} > 10#${ver2[i]} )) && echo "1" && exit
  (( 10#${ver1[i]} < 10#${ver2[i]} )) && echo "-1" && exit
done

# All fields are equivalent.
echo "0"