syntax error...

I have already installed autoconf-2.10 successfully. when I am trying to 
install autoconf-2.50 by using sh ./configure I got list of error message on my 
terminal as below
 
:command not found
./configure: line 16: syntax error near unexpected token 'elif'
./configure:line16:'elif test -n "${BASH_VERSION->set}" && (set -o posix) 
>/dev/null 2>&1;then
 
what is the wrong. Please help me.

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