string comparation

a.sh

#! /bin/bash

# if [ $1 = '' ]; then
# if [ -n $1 ]; then
if [ -n "$1" ]; then
  echo 'arg1 length > 0'
else
  echo 'arg1 length = 0'
fi

# if [ $1 = 'unk' ]; then
if [ " $1" = ' unk' ]; then
  echo 'unk; ok'
else
  echo "$1 is NOT unk; error" 1>&2
  exit 1
fi

echo 'end'

# ref. http://shellscript.sunone.me/if_and_test.html
#      http://furyo.on-air.ne.jp/linux/bash.html
#      http://x68000.q-e-d.net/~68user/unix/pickup?keyword=unexpected&target=command

# qiita: http://qiita.com/items/4e6a7f9623e03b043ddd