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197 lines
6.2 KiB
ReStructuredText
197 lines
6.2 KiB
ReStructuredText
test - perform tests on files and text
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======================================
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Synopsis
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--------
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test [EXPRESSION]
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[ [EXPRESSION] ]
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Description
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-----------
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Tests the expression given and sets the exit status to 0 if true, and 1 if false. An expression is made up of one or more operators and their arguments.
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The first form (``test``) is preferred. For compatibility with other shells, the second form is available: a matching pair of square brackets (``[ [EXPRESSION ] ]``).
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This test is mostly POSIX-compatible.
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When using a variable as an argument for a test operator you should almost always enclose it in double-quotes. There are only two situations it is safe to omit the quote marks. The first is when the argument is a literal string with no whitespace or other characters special to the shell (e.g., semicolon). For example, ``test -b /my/file``. The second is using a variable that expands to exactly one element including if that element is the empty string (e.g., ``set x ''``). If the variable is not set, set but with no value, or set to more than one value you must enclose it in double-quotes. For example, ``test "$x" = "$y"``. Since it is always safe to enclose variables in double-quotes when used as ``test`` arguments that is the recommended practice.
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Operators for files and directories
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-----------------------------------
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- ``-b FILE`` returns true if ``FILE`` is a block device.
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- ``-c FILE`` returns true if ``FILE`` is a character device.
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- ``-d FILE`` returns true if ``FILE`` is a directory.
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- ``-e FILE`` returns true if ``FILE`` exists.
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- ``-f FILE`` returns true if ``FILE`` is a regular file.
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- ``-g FILE`` returns true if ``FILE`` has the set-group-ID bit set.
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- ``-G FILE`` returns true if ``FILE`` exists and has the same group ID as the current user.
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- ``-k FILE`` returns true if ``FILE`` has the sticky bit set. If the OS does not support the concept it returns false. See https://en.wikipedia.org/wiki/Sticky_bit.
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- ``-L FILE`` returns true if ``FILE`` is a symbolic link.
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- ``-O FILE`` returns true if ``FILE`` exists and is owned by the current user.
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- ``-p FILE`` returns true if ``FILE`` is a named pipe.
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- ``-r FILE`` returns true if ``FILE`` is marked as readable.
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- ``-s FILE`` returns true if the size of ``FILE`` is greater than zero.
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- ``-S FILE`` returns true if ``FILE`` is a socket.
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- ``-t FD`` returns true if the file descriptor ``FD`` is a terminal (TTY).
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- ``-u FILE`` returns true if ``FILE`` has the set-user-ID bit set.
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- ``-w FILE`` returns true if ``FILE`` is marked as writable; note that this does not check if the filesystem is read-only.
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- ``-x FILE`` returns true if ``FILE`` is marked as executable.
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Operators for text strings
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--------------------------
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- ``STRING1 = STRING2`` returns true if the strings ``STRING1`` and ``STRING2`` are identical.
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- ``STRING1 != STRING2`` returns true if the strings ``STRING1`` and ``STRING2`` are not identical.
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- ``-n STRING`` returns true if the length of ``STRING`` is non-zero.
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- ``-z STRING`` returns true if the length of ``STRING`` is zero.
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Operators to compare and examine numbers
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----------------------------------------
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- ``NUM1 -eq NUM2`` returns true if ``NUM1`` and ``NUM2`` are numerically equal.
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- ``NUM1 -ne NUM2`` returns true if ``NUM1`` and ``NUM2`` are not numerically equal.
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- ``NUM1 -gt NUM2`` returns true if ``NUM1`` is greater than ``NUM2``.
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- ``NUM1 -ge NUM2`` returns true if ``NUM1`` is greater than or equal to ``NUM2``.
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- ``NUM1 -lt NUM2`` returns true if ``NUM1`` is less than ``NUM2``.
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- ``NUM1 -le NUM2`` returns true if ``NUM1`` is less than or equal to ``NUM2``.
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Both integers and floating point numbers are supported.
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Operators to combine expressions
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--------------------------------
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- ``COND1 -a COND2`` returns true if both ``COND1`` and ``COND2`` are true.
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- ``COND1 -o COND2`` returns true if either ``COND1`` or ``COND2`` are true.
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Expressions can be inverted using the ``!`` operator:
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- ``! EXPRESSION`` returns true if ``EXPRESSION`` is false, and false if ``EXPRESSION`` is true.
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Expressions can be grouped using parentheses.
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- ``( EXPRESSION )`` returns the value of ``EXPRESSION``.
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Note that parentheses will usually require escaping with ``\(`` to avoid being interpreted as a command substitution.
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Examples
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--------
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If the ``/tmp`` directory exists, copy the ``/etc/motd`` file to it:
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::
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if test -d /tmp
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cp /etc/motd /tmp/motd
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end
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If the variable ``MANPATH`` is defined and not empty, print the contents. (If ``MANPATH`` is not defined, then it will expand to zero arguments, unless quoted.)
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::
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if test -n "$MANPATH"
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echo $MANPATH
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end
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Parentheses and the ``-o`` and ``-a`` operators can be combined to produce more complicated expressions. In this example, success is printed if there is a ``/foo`` or ``/bar`` file as well as a ``/baz`` or ``/bat`` file.
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::
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if test \( -f /foo -o -f /bar \) -a \( -f /baz -o -f /bat \)
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echo Success.
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end.
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Numerical comparisons will simply fail if one of the operands is not a number:
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::
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if test 42 -eq "The answer to life, the universe and everything"
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echo So long and thanks for all the fish # will not be executed
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end
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A common comparison is with $status:
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::
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if test $status -eq 0
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echo "Previous command succeeded"
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end
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The previous test can likewise be inverted:
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::
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if test ! $status -eq 0
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echo "Previous command failed"
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end
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which is logically equivalent to the following:
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::
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if test $status -ne 0
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echo "Previous command failed"
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end
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Standards
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---------
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``test`` implements a subset of the <a href="http://www.unix.com/man-page/POSIX/1/test/">IEEE Std 1003.1-2008 (POSIX.1) standard</a>. The following exceptions apply:
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- The ``<`` and ``>`` operators for comparing strings are not implemented.
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- Because this test is a shell builtin and not a standalone utility, using the -c flag on a special file descriptors like standard input and output may not return the same result when invoked from within a pipe as one would expect when invoking the ``test`` utility in another shell.
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In cases such as this, one can use ``command`` ``test`` to explicitly use the system's standalone ``test`` rather than this ``builtin`` ``test``.
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