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docs/test: Simplify
A bit stuffy, also link to string/path
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Fabian Boehm
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1 changed files with 11 additions and 24 deletions
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@ -11,7 +11,6 @@ Synopsis
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test [EXPRESSION]
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[ [EXPRESSION] ]
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Description
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-----------
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@ -21,13 +20,11 @@ Description
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To see the documentation on the ``test`` command you might have,
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use ``command man test``.
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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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``test`` checks the given conditions and sets the exit status to 0 if they are true, 1 if they are false.
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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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When using a variable as an argument with ``test`` you should almost always enclose it in double-quotes, as variables expanding to zero or more than one argument will most likely interact badly with ``test``.
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Operators for files and directories
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-----------------------------------
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@ -163,8 +160,6 @@ Examples
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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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@ -174,8 +169,6 @@ If the ``/tmp`` directory exists, copy the ``/etc/motd`` file to it:
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If the variable :envvar:`MANPATH` is defined and not empty, print the contents. (If :envvar:`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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@ -185,8 +178,6 @@ If the variable :envvar:`MANPATH` is defined and not empty, print the contents.
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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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@ -196,30 +187,22 @@ Parentheses and the ``-o`` and ``-a`` operators can be combined to produce more
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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 :envvar:`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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@ -229,8 +212,6 @@ The previous test can likewise be inverted:
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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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@ -241,10 +222,16 @@ which is logically equivalent to the following:
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Standards
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---------
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``test`` implements a subset of the `IEEE Std 1003.1-2008 (POSIX.1) standard <https://www.unix.com/man-page/posix/1p/test/>`__. The following exceptions apply:
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Unlike many things in fish, ``test`` implements a subset of the `IEEE Std 1003.1-2008 (POSIX.1) standard <https://www.unix.com/man-page/posix/1p/test/>`__. 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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See also
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--------
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Other commands that may be useful as a condition, and are often easier to use:
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- :doc:`string`, which can do string operations including wildcard and regular expression matching
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- :doc:`path`, which can do file checks and operations, including filters on multiple paths at once
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