++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Lista dostepnych operatorow, wyciagnieta z manuala "ksh"

-a file
    TRUE, if file exists.

-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.

-f file
    TRUE, if file exists and is an ordinary file.

-g file
    TRUE, if file exists and has its setgid bit set.

-G file
    TRUE, if file exists and its group matches the effective group ID of
    this process.

-k file
    TRUE, if file exists and has its sticky bit set.

-L file
    TRUE, if file exists and is a symbolic link.

-n string
    TRUE, if length of string is nonzero.

-o  option
    TRUE, if option named option is on.

-O file
    TRUE, if file exists and is owned by the effective user ID of this pro-
    cess.

-p file
    TRUE, if file exists and is a FIFO special file or a pipe.

-r file
    TRUE, if file exists and is readable by current process.

-s file
    TRUE, if file exists and has size greater than 0 (zero).

-S file
    TRUE, if file exists and is a socket.

-t file_des
    TRUE, if file descriptor number file_des is open and associated with a
    terminal device.

-u file
    TRUE, if file exists and has its setuid bit set.

-w file
    TRUE, if file exists and is writable by current process.

-x file
    TRUE, if file exists and is executable by current process.  If file
    exists and is a directory, then the current process has permission to
    search in the directory.

-z string
    TRUE, if length of string is 0 (zero).

file1 -nt file2
    TRUE, if file1 exists and is newer than file2.

file1 -ot file2
    TRUE, if file1 exists and is older than file2.

file1 -ef file2
    TRUE, if file1 and file2 exist and refer to the same file.

string = pattern
    TRUE, if string matches pattern.

string != pattern
    TRUE, if string does not match pattern.

string1 < string2
    TRUE, if string1 collates before string2.

string1 > string2
    TRUE, if string1 collates after string2.

expression1 -eq expression2
    TRUE, if expression1 is equal to expression2.

expression1 -ne expression2
    TRUE, if expression1 is not equal to expression2.

expression1 -lt expression2
    TRUE, if expression1 is less than expression2.

expression1 -gt expression2
    TRUE, if expression1 is greater than expression2.

expression1 -le expression2
    TRUE, if expression1 is less than or equal to expression2.

expression1 -ge expression2
    TRUE, if expression1 is greater than or equal to expression2.

A compound expression can be constructed from these primitives by using any
of the following, listed in decreasing order of precedence.

(expression)
    TRUE, if expression is TRUE.  Used to group expressions.

! expression
    TRUE if expression is FALSE.

expression1 && expression2
    TRUE, if expression1 and expression2 are both TRUE.

expression1 || expression2
    TRUE, if either expression1 or expression2 is TRUE.