shell if -n -z -f -z ...

➜  ~ man test


TEST(1)                   BSD General Commands Manual                  TEST(1)

NAME
     test, [ -- condition evaluation utility

SYNOPSIS
     test expression
     [ expression ]

DESCRIPTION
     The test utility evaluates the expression and, if it evaluates to true, returns a zero (true) exit status; otherwise it returns 1 (false).  If there is no expression, test also
     returns 1 (false).

     All operators and flags are separate arguments to the test utility.

     The following primaries are used to construct expression:

     -b file       True if file exists and is a block special file.

     -c file       True if file exists and is a character special file.

     -d file       True if file exists and is a directory.

     -e file       True if file exists (regardless of type).

     -f file       True if file exists and is a regular file.

     -g file       True if file exists and its set group ID flag is set.

     -h file       True if file exists and is a symbolic link.  This operator is retained for compatibility with previous versions of this program.  Do not rely on its existence;
                   use -L instead.

     -k file       True if file exists and its sticky bit is set.

     -n string     True if the length of string is nonzero.

     -p file       True if file is a named pipe (FIFO).

     -r file       True if file exists and is readable.

     -s file       True if file exists and has a size greater than zero.

     -t file_descriptor
                   True if the file whose file descriptor number is file_descriptor is open and is associated with a terminal.

     -u file       True if file exists and its set user ID flag is set.

     -w file       True if file exists and is writable.  True indicates only that the write flag is on.  The file is not writable on a read-only file system even if this test indi-
                   cates true.

     -x file       True if file exists and is executable.  True indicates only that the execute flag is on.  If file is a directory, true indicates that file can be searched.

     -z string     True if the length of string is zero.

     -L file       True if file exists and is a symbolic link.

     -O file       True if file exists and its owner matches the effective user id of this process.

     -G file       True if file exists and its group matches the effective group id of this process.

     -S file       True if file exists and is a socket.