Unbuntu Run a shell script problem

Today learn bird's private dishes, according to the book hit a few shell script, but the total error

The first is to use [] to determine the condition, = = does not work properly

The second is to declare variables in the script to use declare, always error said, not found

Find the reason on the Internet, say is the Ubuntu uses the dash instead of bash, so when executes the script to hit like the command sh scriptfile.sh to be possible the error (at this time uses dash),

But it's no problem knocking on the command bash scriptfile.sh.

To change dash back to bash, just execute the sudo dpkg-reconfigure dash and select < no > in the Interactive interface

For reference, see

Http://www.cnblogs.com/Trekshot/archive/2010/03/29/1699383.html

Unbuntu Run a shell script problem