texinode(Conditional Expressions)(Prompt Expansion)(Arithmetic Evaluation)(Top)
chapter(Conditional Expressions)
ifzman(\
sect(Conditional Expressions)
)\
cindex(conditional expressions)
cindex(expressions, conditional)
A em(conditional expression) is used with the tt([[)
compound command to test attributes of files and to compare strings.
Each expression can be constructed from one or more
of the following unary or binary expressions:

startitem()
item(tt(-a) var(file))(
true if var(file) exists.
)
item(tt(-b) var(file))(
true if var(file) exists and is a block special file.
)
item(tt(-c) var(file))(
true if var(file) exists and is a character special file.
)
item(tt(-d) var(file))(
true if var(file) exists and is a directory.
)
item(tt(-e) var(file))(
true if var(file) exists.
)
item(tt(-f) var(file))(
true if var(file) exists and is a regular file.
)
item(tt(-g) var(file))(
true if var(file) exists and has its setgid bit set.
)
item(tt(-h) var(file))(
true if var(file) exists and is a symbolic link.
)
item(tt(-k) var(file))(
true if var(file) exists and has its sticky bit set.
)
item(tt(-n) var(string))(
true if length of var(string) is non-zero.
)
item(tt(-o) var(option))(
true if option named var(option) is on.  var(option)
may be a single character, in which case it is a single letter option name.
(See noderef(Specifying Options).)
)
item(tt(-p) var(file))(
true if var(file) exists and is a FIFO special file (named pipe).
)
item(tt(-r) var(file))(
true if var(file) exists and is readable by current process.
)
item(tt(-s) var(file))(
true if var(file) exists and has size greater than zero.
)
item(tt(-t) var(fd))(
true if file descriptor number var(fd)
is open and associated with a terminal device.
(note: var(fd) is not optional)
)
item(tt(-u) var(file))(
true if var(file) exists and has its setuid bit set.
)
item(tt(-w) var(file))(
true if var(file) exists and is writable by current process.
)
item(tt(-x) var(file))(
true if var(file) exists and is executable by current process.
If var(file) exists and is a directory, then the current process
has permission to search in the directory.
)
item(tt(-z) var(string))(
true if length of var(string) is zero.
)
item(tt(-L) var(file))(
true if var(file) exists and is a symbolic link.
)
item(tt(-O) var(file))(
true if var(file) exists and is owned by the effective user ID of this process.
)
item(tt(-G) var(file))(
true if var(file) exists and its group matches
the effective group ID of this process.
)
item(tt(-S) var(file))(
true if var(file) exists and is a socket.
)
item(tt(-N) var(file))(
true if var(file) exists and its access time is
not newer than its modification time.
)
item(var(file1) tt(-nt) var(file2))(
true if var(file1) exists and is newer than var(file2).
)
item(var(file1) tt(-ot) var(file2))(
true if var(file1) exists and is older than var(file2).
)
item(var(file1) tt(-ef) var(file2))(
true if var(file1) and var(file2) exist and refer to the same file.
)
xitem(var(string) tt(=) var(pattern))
item(var(string) tt(==) var(pattern))(
true if var(string) matches var(pattern).
The `tt(==)' form is the preferred one.  The `tt(=)' form is for
backward compatibility and should be considered obsolete.
)
item(var(string) tt(!=) var(pattern))(
true if var(string) does not match var(pattern).
)
item(var(string1) tt(<) var(string2))(
true if var(string1) comes before var(string2)
based on ASCII value of their characters.
)
item(var(string1) tt(>) var(string2))(
true if var(string1) comes after var(string2)
based on ASCII value of their characters.
)
item(var(exp1) tt(-eq) var(exp2))(
true if var(exp1) is numerically equal to var(exp2).
)
item(var(exp1) tt(-ne) var(exp2))(
true if var(exp1) is numerically not equal to var(exp2).
)
item(var(exp1) tt(-lt) var(exp2))(
true if var(exp1) is numerically less than var(exp2).
)
item(var(exp1) tt(-gt) var(exp2))(
true if var(exp1) is numerically greater than var(exp2).
)
item(var(exp1) tt(-le) var(exp2))(
true if var(exp1) is numerically less than or equal to var(exp2).
)
item(var(exp1) tt(-ge) var(exp2))(
true if var(exp1) is numerically greater than or equal to var(exp2).
)
item(tt(LPAR()) var(exp) tt(RPAR()))(
true if var(exp) is true.
)
item(tt(!) var(exp))(
true if var(exp) is false.
)
item(var(exp1) tt(&&) var(exp2))(
true if var(exp1) and var(exp2) are both true.
)
item(var(exp1) tt(||) var(exp2))(
true if either var(exp1) or var(exp2) is true.
)
enditem()

Normal shell expansion is performed on the var(file), var(string) and
var(pattern) arguments, but the result of each expansion is constrained to
be a single word, similar to the effect of double quotes.  However, pattern
metacharacters are active for the var(pattern) arguments; the patterns
are the same as those used for filename generation, see
ifzman(\
zmanref(zshexpn)\
)\
ifnzman(\
noderef(Filename Generation)\
)\
, but there is no special behaviour
of `tt(/)' nor initial dots, and no glob qualifiers are allowed.

In each of the above expressions, if
var(file) is of the form `tt(/dev/fd/)var(n)',
where var(n) is an integer,
then the test applied to the open file whose
descriptor number is var(n),
even if the underlying system does not support
the tt(/dev/fd) directory.

In the forms which do numeric comparison, the expressions var(exp)
undergo arithmetic expansion as if they were enclosed in tt($((...))).

For example, the following:

example([[ ( -f foo || -f bar ) && $report = y* ]] && print File exists.)

tests if either file tt(foo) or file tt(bar) exists, and if so, if the
value of the parameter tt(report) begins with `tt(y)'; if the complete
condition is true, the message `tt(File exists.)' is printed.
