rbenv/libexec/rbenv-version-file-read

#!/usr/bin/env bash
set -e

VERSION_FILE="$1"

if [ -e "$VERSION_FILE" ]; then
  # Read and print the first non-whitespace word from the specified
  # version file.
  while read -a words; do
    version="${words[0]}"
    if [ -n "$version" ]; then
      echo "$version"
      break
    fi
  done < <( cat "$VERSION_FILE" && echo )
else
  exit 1
fi