Shell Programming and Scripting

   if [[ ! ${user_input} =~ [^[:space:]] ]] ; then
        echo "Blanks are NOT a valid input "
        return 1
   fi

syntax error at line 142 : `=~' unexpected

$ VALUE=
$ echo $VALUE | grep -E '^[:space]*$'

$ echo $?
0
$  VALUE=1
$ echo $VALUE | grep -E '^[:space]*$'
$ echo $?
1

$ echo $VALUE
1
$ perl -e 'print "BAD_USER\n" if $ARGV[0] =~/^\s*$/' $VALUE
$ VALUE=
$ echo $VALUE | perl -e 'print "BAD_USER\n" if/^\s*$/'
BAD_USER