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

谁借莪１个温暖的怀抱￠ 2022-11-02 13:22 168阅读 0赞

➜  ~ 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.