Shell脚本中如何判断一个命令是否存在 ​

if command -v java >/dev/null 2>&1; then
  echo 'exists java'
else
  echo 'no exists java'
fi

if command -v java >/dev/null 2>&1; then
  echo 'exists java'
else
  echo 'no exists java'
fi

if type java >/dev/null 2>&1; then
  echo 'exists java'
else
  echo 'no exists java'
fi

if type java >/dev/null 2>&1; then
  echo 'exists java'
else
  echo 'no exists java'
fi

if hash java 2>/dev/null; then
  echo 'exists java'
else
  echo 'no exists java'
fi

if hash java 2>/dev/null; then
  echo 'exists java'
else
  echo 'no exists java'
fi