我的脚本命令不识别了！

zzzzyb

相关代码如下：
/mnt/app/usr/daemon # ./updataapp.sh
Shell invoked to run file: ./updataapp.sh
Command: #!/bin/sh
Command: echo $"Start updataApp program script comman"
Start updataApp program script comman
Command:
Command: echo "now work directory: "
now work directory:
Command: /bin/pwd
/mnt/app/usr/daemon
Command:
Command: APP_PATH=../app
Command: DOWNLOAD_PATH=../tmp/downloadApp
Command: UPDATE_PATH=../tmp/updataApp
Command: BACKUP_PATH=../tmp/backApp
Command: BACKUP_FILE=app.tar
Command: APP_FILENAME=app
Command:
Command: echo  "check directory..."
check directory...
Command: if [[ -z "$APP_PATH" ]]
if: Bad command or file name          //if条件不识别！！！
Command:  then
then: Bad command or file name
Command:

大虾指点下，有什么问题，我目前的环境是在开发板跑uClinux，使用据说是可以识别if命令的hush shell，上面相关代码在linux虚拟机上可以正常运行。