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(-v) var(varname))(
true if shell variable var(varname) is 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 two forms are exactly equivalent.  The `tt(=)' form is
the traditional shell syntax (and hence the only one generally used
with the tt(test) and tt([) builtins); the `tt(==)' form provides
compatibility with other sorts of computer language.
)
item(var(string) tt(!=) var(pattern))(
true if var(string) does not match var(pattern).
)
item(var(string) tt(=~) var(regexp))(
true if var(string) matches the regular expression
var(regexp).  If the option tt(RE_MATCH_PCRE) is set
var(regexp) is tested as a PCRE regular expression using
the tt(zsh/pcre) module, else it is tested as a POSIX
extended regular expression using the tt(zsh/regex) module.
Upon successful match, some variables will be updated; no variables
are changed if the matching fails.

If the option tt(BASH_REMATCH) is not set the scalar parameter
tt(MATCH) is set to the substring that matched the pattern and
the integer parameters tt(MBEGIN) and tt(MEND) to the index of the start
and end, respectively, of the match in var(string), such that if
var(string) is contained in variable tt(var) the expression
`tt(${var[$MBEGIN,$MEND]})' is identical to `tt($MATCH)'.  The setting
of the option tt(KSH_ARRAYS) is respected.  Likewise, the array
tt(match) is set to the substrings that matched parenthesised
subexpressions and the arrays tt(mbegin) and tt(mend) to the indices of
the start and end positions, respectively, of the substrings within
var(string).  The arrays are not set if there were no parenthesised
subexpresssions.  For example, if the string `tt(a short string)' is matched
against the regular expression `tt(s+LPAR()...RPAR()t)', then (assuming the
option tt(KSH_ARRAYS) is not set) tt(MATCH), tt(MBEGIN)
and tt(MEND) are `tt(short)', tt(3) and tt(7), respectively, while tt(match),
tt(mbegin) and tt(mend) are single entry arrays containing
the strings `tt(hor)', `tt(4)' and `tt(6)', respectively.

If the option tt(BASH_REMATCH) is set the array
tt(BASH_REMATCH) is set to the substring that matched the pattern
followed by the substrings that matched parenthesised
subexpressions within the 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).
Note that for purely numeric comparisons use of the
tt(LPAR()LPAR())var(...)tt(RPAR()RPAR()) builtin described in
ifzman(the section `ARITHMETIC EVALUATION')\
ifnzman(noderef(Arithmetic Evaluation)) is more convenient than
conditional expressions.
)
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()

For compatibility, if there is a single argument that is not
syntactically significant, typically a variable, the condition is
treated as a test for whether the expression expands as a string of
non-zero length.  In other words, tt([[ $var ]]) is the same as tt([[ -n
$var ]]).  It is recommended that the second, explicit, form be used
where possible.

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.

Filename generation is not performed on any form of argument to
conditions.  However, it can be forced in any case where normal shell
expansion is valid and when the option tt(EXTENDED_GLOB) is in effect by
using an explicit glob qualifier of the form tt(LPAR()#q+RPAR()) at the
end of the string.  A normal glob qualifier expression may appear
between the `tt(q)' and the closing parenthesis; if none appears the
expression has no effect beyond causing filename generation.  The
results of filename generation are joined together to form a single
word, as with the results of other forms of expansion.

This special use of filename generation is only available with the
tt([[) syntax.  If the condition occurs within the tt([) or tt(test)
builtin commands then globbing occurs instead as part of normal command
line expansion before the condition is evaluated.  In this case it may
generate multiple words which are likely to confuse the syntax of the
test command.

For example,

example([[ -n file*(#qN) ]])

produces status zero if and only if there is at least one file in the
current directory beginning with the string `tt(file)'.  The globbing
qualifier tt(N) ensures that the expression is empty if there is
no matching file.

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($LPAR()LPAR())var(...)tt(RPAR()RPAR()).

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.