Description
The test command evaluates the expression parameter. In some shells (such as FreeBSD sh(1)), it is actually a shell builtin, even though external version still exists. In the second form of the command, the (brackets) must be surrounded by blank spaces, this is because /bin/[ is a program and POSIX compatible shells require a space between the program name and its arguments. You must test explicitly for file names in the C shell. File-name substitution (globbing) causes the shell script to exit. Functions and operators are treated as separate parameters by the test command. The expression parameter refers to a statement that is checked for a true or false condition.
Read more about this topic: Test (Unix)
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