Originální popis anglicky:
test - evaluate expression
Návod, kniha: POSIX Programmer's Manual
test [expression]
[
[expression] ]
The
test utility shall evaluate the
expression and indicate the
result of the evaluation by its exit status. An exit status of zero indicates
that the expression evaluated as true and an exit status of 1 indicates that
the expression evaluated as false.
In the second form of the utility, which uses
"[]" rather than
test, the application shall ensure that the square brackets are
separate arguments.
The
test utility shall not recognize the
"--" argument
in the manner specified by guideline 10 in the Base Definitions volume of
IEEE Std 1003.1-2001, Section 12.2, Utility Syntax Guidelines.
No options shall be supported.
The application shall ensure that all operators and elements of primaries are
presented as separate arguments to the
test utility.
The following primaries can be 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.
- -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.
- -L file
- True if file exists and is a symbolic link.
- -n string
- True if the length of string is non-zero.
- -p file
- True if file is a FIFO.
- -r file
- True if file exists and is readable. True shall
indicate that permission to read from file will be granted, as
defined in File Read, Write, and Creation .
- -S file
- True if file exists and is a socket.
- -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 shall
indicate that permission to write from file will be granted, as
defined in File Read, Write, and Creation .
- -x file
- True if file exists and is executable. True shall
indicate that permission to execute file will be granted, as
defined in File Read, Write, and Creation . If file is a
directory, true shall indicate that permission to search file will
be granted.
- -z string
- True if the length of string string is zero.
- string
- True if the string string is not the null
string.
- s1 = s2
- True if the strings s1 and s2 are
identical.
- s1 != s2
- True if the strings s1 and s2 are not
identical.
- n1 -eq n2
- True if the integers n1 and n2 are
algebraically equal.
- n1 -ne n2
- True if the integers n1 and n2 are not
algebraically equal.
- n1 -gt n2
- True if the integer n1 is algebraically greater than
the integer n2.
- n1 -ge n2
- True if the integer n1 is algebraically greater than
or equal to the integer n2.
- n1 -lt n2
- True if the integer n1 is algebraically less than
the integer n2.
- n1 -le n2
- True if the integer n1 is algebraically less than or
equal to the integer n2.
- expression1 -a
expression2
-
True if both expression1 and expression2 are true. The
-a binary primary is left associative. It has a higher precedence
than -o.
- expression1 -o
expression2
-
True if either expression1 or expression2 is true. The
-o binary primary is left associative.
With the exception of the
-h file and
-L file
primaries, if a
file argument is a symbolic link,
test shall
evaluate the expression by resolving the symbolic link and using the file
referenced by the link.
These primaries can be combined with the following operators:
- ! expression
- True if expression is false.
- ( expression )
- True if expression is true. The parentheses can be
used to alter the normal precedence and associativity.
The primaries with two elements of the form:
-primary_operator primary_operand
are known as
unary primaries. The primaries with three elements in either
of the two forms:
primary_operand -primary_operator primary_operand
primary_operand primary_operator primary_operand
are known as
binary primaries. Additional implementation-defined
operators and
primary_operators may be provided by implementations.
They shall be of the form -
operator where the first character of
operator is not a digit.
The algorithm for determining the precedence of the operators and the return
value that shall be generated is based on the number of arguments presented to
test. (However, when using the
"[...]" form, the
right-bracket final argument shall not be counted in this algorithm.)
In the following list, $1, $2, $3, and $4 represent the arguments presented to
test:
- 0 arguments:
- Exit false (1).
- 1 argument:
- Exit true (0) if $1 is not null; otherwise, exit
false.
- 2 arguments:
- *
- If $1 is '!' , exit true if $2 is null, false if $2
is not null.
- *
- If $1 is a unary primary, exit true if the unary test is
true, false if the unary test is false.
- *
- Otherwise, produce unspecified results.
- 3 arguments:
- *
- If $2 is a binary primary, perform the binary test of $1
and $3.
- *
- If $1 is '!' , negate the two-argument test of $2
and $3.
- *
- If $1 is '(' and $3 is ')' , perform the
unary test of $2.
- *
- Otherwise, produce unspecified results.
- 4 arguments:
- *
- If $1 is '!' , negate the three-argument test of $2,
$3, and $4.
- *
- If $1 is '(' and $4 is ')' , perform the
two-argument test of $2 and $3.
- *
- Otherwise, the results are unspecified.
- >4 arguments:
- The results are unspecified.
On XSI-conformant systems, combinations of primaries and operators shall be
evaluated using the precedence and associativity rules described previously.
In addition, the string comparison binary primaries
'=' and
"!=" shall have a higher precedence than any unary primary.
Not used.
None.
The following environment variables shall affect the execution of
test:
- LANG
- Provide a default value for the internationalization
variables that are unset or null. (See the Base Definitions volume of
IEEE Std 1003.1-2001, Section 8.2, Internationalization
Variables for the precedence of internationalization variables used to
determine the values of locale categories.)
- LC_ALL
- If set to a non-empty string value, override the values of
all the other internationalization variables.
- LC_CTYPE
- Determine the locale for the interpretation of sequences of
bytes of text data as characters (for example, single-byte as opposed to
multi-byte characters in arguments).
- LC_MESSAGES
- Determine the locale that should be used to affect the
format and contents of diagnostic messages written to standard error.
- NLSPATH
- Determine the location of message catalogs for the
processing of LC_MESSAGES .
Default.
Not used.
The standard error shall be used only for diagnostic messages.
None.
None.
The following exit values shall be returned:
- 0
- expression evaluated to true.
- 1
- expression evaluated to false or expression
was missing.
- >1
- An error occurred.
Default.
The following sections are informative.
Scripts should be careful when dealing with user-supplied input that could be
confused with primaries and operators. Unless the application writer knows all
the cases that produce input to the script, invocations like:
should be written as:
to avoid problems if a user supplied values such as $1 set to
'!' and $2
set to the null string. That is, in cases where maximal portability is of
concern, replace:
with:
and replace:
with:
but note that, in
test,
-a has higher precedence than
-o
while
"&&" and
"||" have equal
precedence in the shell.
Parentheses or braces can be used in the shell command language to effect
grouping.
Parentheses must be escaped when using
sh; for example:
test \( expr1 -a expr2 \) -o expr3
This command is not always portable outside XSI-conformant systems. The
following form can be used instead:
( test expr1 && test expr2 ) || test expr3
The two commands:
could not be used reliably on some historical systems. Unexpected results would
occur if such a
string expression were used and $1 expanded to
'!' ,
'(' , or a known unary primary. Better constructs are:
test -n "$1"
test -z "$1"
respectively.
Historical systems have also been unreliable given the common construct:
test "$response" = "expected string"
One of the following is a more reliable form:
test "X$response" = "Xexpected string"
test "expected string" = "$response"
Note that the second form assumes that
expected string could not be
confused with any unary primary. If
expected string starts with
'-' ,
'(' ,
'!' , or even
'=' , the first form
should be used instead. Using the preceding rules without the XSI marked
extensions, any of the three comparison forms is reliable, given any input.
(However, note that the strings are quoted in all cases.)
Because the string comparison binary primaries,
'=' and
"!=" , have a higher precedence than any unary primary in the
greater than 4 argument case, unexpected results can occur if arguments are
not properly prepared. For example, in:
If $1 evaluates to a possible directory name of
'=' , the first three
arguments are considered a string comparison, which shall cause a syntax error
when the second
-d is encountered. One of the following forms prevents
this; the second is preferred:
test \( -d "$1" \) -o \( -d "$2" \)
test -d "$1" || test -d "$2"
Also in the greater than 4 argument case:
test "$1" = "bat" -a "$2" = "ball"
syntax errors occur if $1 evaluates to
'(' or
'!' . One of the
following forms prevents this; the third is preferred:
test "X$1" = "Xbat" -a "X$2" = "Xball"
test "$1" = "bat" && test "$2" = "ball"
test "X$1" = "Xbat" && test "X$2" = "Xball"
- 1.
- Exit if there are not two or three arguments (two
variations):
if [ $# -ne 2 -a $# -ne 3 ]; then exit 1; fi
if [ $# -lt 2 -o $# -gt 3 ]; then exit 1; fi
- 2.
- Perform a mkdir if a directory does not exist:
test ! -d tempdir && mkdir tempdir
- 3.
- Wait for a file to become non-readable:
while test -r thefile
do
sleep 30
done
echo '"thefile" is no longer readable'
- 4.
- Perform a command if the argument is one of three strings
(two variations):
if [ "$1" = "pear" ] || [ "$1" = "grape" ] || [ "$1" = "apple" ]
then
command
fi
case "$1" in
pear|grape|apple) command ;;
esac
The KornShell-derived conditional command (double bracket
[[]]) was
removed from the shell command language description in an early proposal.
Objections were raised that the real problem is misuse of the
test
command (
[), and putting it into the shell is the wrong way to fix the
problem. Instead, proper documentation and a new shell reserved word (
!) are sufficient.
Tests that require multiple
test operations can be done at the shell
level using individual invocations of the
test command and shell
logicals, rather than using the error-prone
-o flag of
test.
XSI-conformant systems support more than four arguments.
XSI-conformant systems support the combining of primaries with the following
constructs:
- expression1 -a expression2
-
True if both expression1 and expression2 are true.
- expression1 -o expression2
-
True if at least one of expression1 and expression2 are
true.
- ( expression )
-
True if expression is true.
In evaluating these more complex combined expressions, the following precedence
rules are used:
- *
- The unary primaries have higher precedence than the
algebraic binary primaries.
- *
- The unary primaries have lower precedence than the string
binary primaries.
- *
- The unary and binary primaries have higher precedence than
the unary string primary.
- *
- The ! operator has higher precedence than the
-a operator, and the -a operator has higher precedence than
the -o operator.
- *
- The -a and -o operators are left
associative.
- *
- The parentheses can be used to alter the normal precedence
and associativity.
The BSD and System V versions of
-f are not the same. The BSD definition
was:
- -f file
- True if file exists and is not a directory.
The SVID version (true if the file exists and is a regular file) was chosen for
this volume of IEEE Std 1003.1-2001 because its use is
consistent with the
-b,
-c,
-d, and
-p operands (
file exists and is a specific file type).
The
-e primary, possessing similar functionality to that provided by the
C shell, was added because it provides the only way for a shell script to find
out if a file exists without trying to open the file. Since implementations
are allowed to add additional file types, a portable script cannot use:
test -b foo -o -c foo -o -d foo -o -f foo -o -p foo
to find out if
foo is an existing file. On historical BSD systems, the
existence of a file could be determined by:
but there was no easy way to determine that an existing file was a regular file.
An early proposal used the KornShell
-a primary (with the same
meaning), but this was changed to
-e because there were concerns about
the high probability of humans confusing the
-a primary with the
-a binary operator.
The following options were not included in this volume of
IEEE Std 1003.1-2001, although they are provided by some
implementations. These operands should not be used by new implementations for
other purposes:
- -k file
- True if file exists and its sticky bit is set.
- -C file
- True if file is a contiguous file.
- -V file
- True if file is a version file.
The following option was not included because it was undocumented in most
implementations, has been removed from some implementations (including System
V), and the functionality is provided by the shell (see
Parameter
Expansion .
- -l string
- The length of the string string.
The
-b,
-c,
-g,
-p,
-u, and
-x
operands are derived from the SVID; historical BSD does not provide them. The
-k operand is derived from System V; historical BSD does not provide
it.
On historical BSD systems,
test -w directory always
returned false because
test tried to open the directory for writing,
which always fails.
Some additional primaries newly invented or from the KornShell appeared in an
early proposal as part of the conditional command (
[[]]):
s1
> s2,
s1 < s2,
str =
pattern,
str != pattern,
f1 -nt
f2,
f1 -ot f2, and
f1 -ef f2.
They were not carried forward into the
test utility when the
conditional command was removed from the shell because they have not been
included in the
test utility built into historical implementations of
the
sh utility.
The
-t file_descriptor primary is shown with a mandatory argument
because the grammar is ambiguous if it can be omitted. Historical
implementations have allowed it to be omitted, providing a default of 1.
None.
File Read, Write, and Creation ,
find
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard, the original
IEEE and The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.opengroup.org/unix/online.html
.
