Shell script Execution Error [: 0:unary operator expected

When executing shell script, if judgment statement error

#!/bin/bashif [0 = = $testNum]then    echo "Check result:0" fi

　　

Testnum is not defined when used, no assignment is empty (originally defined, just a clerical error is similar to tsetnum), after performing the conversion is actually

if [0 = =  ]

Not equal, and less [symbolic error; circumvent the following

#!/bin/bashif [[0 = = $testNum]]then    echo "Check result:0" fi

Use "[[]]" to determine, or add a single character

#!/bin/bashif ["0" x = = "$testNumx" x]then    echo "Check result:0" fi

　　

In fact, for my mistakes, of course, the use of "[]" ordinary judgment as good, you can check the error, but this implementation is mostly used to determine whether the value of the query or other conditions given by the value is satisfied with the condition, the existence of NULL is the normal scene, so to improve their own code.

Detailed meaning to be added

Shell script Execution Error [: 0:unary operator expected