Merge patch series "regex patches"

Rasmus Villemoes <ravi@prevas.dk> says:

This started as a rather simple patch, 1/12, adding the ability to
more conveniently do regex matching in shell.

But with that, it became very easy to see what the slre library can
and especially what it cannot do, and that way I found both outright
bugs and a "wow, doesn't it support that syntax" gotcha. I couldn't
find any tests ('git grep slre -- test/' was empty), so I added a
small test suite and tweaked slre.c.

Link: https://lore.kernel.org/r/20250513084034.654865-1-ravi@prevas.dk

2 files changed, 105 insertions, 2 deletions

diff --git a/doc/usage/cmd/setexpr.rst b/doc/usage/cmd/setexpr.rst
index 593a0ea91e1..5bc37ae50fc 100644
--- a/doc/usage/cmd/setexpr.rst
+++ b/doc/usage/cmd/setexpr.rst
@@ -144,8 +144,9 @@ Configuration
 
 * The *setexpr* command is only available if CMD_SETEXPR=y.
 * The *setexpr fmt* sub-command is only available if CMD_SETEXPR_FMT=y.
-* The *setexpr gsub* and *setexpr sub* sub-commands are only available if
-  CONFIG_REGEX=y.
+* The *setexpr gsub* and *setexpr sub* sub-commands are only available
+  if CONFIG_REGEX=y. For an overview of the supported regex syntax,
+  see :doc:`test`.
 
 Return value
 ------------
diff --git a/doc/usage/cmd/test.rst b/doc/usage/cmd/test.rst
new file mode 100644
index 00000000000..d1379117fca
--- /dev/null
+++ b/doc/usage/cmd/test.rst
@@ -0,0 +1,102 @@
+.. SPDX-License-Identifier: GPL-2.0-or-later
+
+.. index::
+   single: test (command)
+
+test command
+============
+
+Synopsis
+--------
+
+::
+
+    test <str-op> <s>
+    test <s1> <str-cmp> <s2>
+    test <n1> <num-cmp> <n2>
+    test ! <expr>
+    test <expr1> -o <expr2>
+    test <expr1> -a <expr2>
+    test -e <interface> <dev[:part]> <path>
+    test <s> =~ <re>
+
+Description
+-----------
+
+The ``test`` command is similar to the ordinary shell built-in by the
+same name. Unlike in ordinary shells, it cannot be spelled ``[``.
+
+Strings
+~~~~~~~
+
+The string tests ``-n`` and ``-z``, and string comparison operators
+``=``, ``!=``, ``<`` and ``>``, work exactly as in ordinary shells.
+
+Numbers
+~~~~~~~
+
+The number comparison operators ``-lt``, ``-le``, ``-gt``, ``-gt``,
+``-eq`` and ``-ne`` work as in ordinary shells.
+
+.. note::
+  Numbers are parsed with ``simple_strtol(, 0)``, meaning that they
+  are treated as decimal unless there is a `0x` prefix, any errors in
+  parsing are ignored, and parsing stops as soon as a non-digit (for
+  the selected base) is encountered. And most U-Boot commands that
+  generate "numeric" environment variables store them as hexadecimal
+  *without* a `0x` prefix.
+
+For example, this is not a correct way of testing whether a given file
+has a size less than 4KiB::
+
+  # Assuming readme.txt exists, sets 'filesize' environment variable
+  $ size mmc 0:1 readme.txt
+  $ if test "$filesize" -lt 4096 ; then ...
+
+If the file size is actually 8000 (decimal), its hexadecimal
+representation, and thus the value of ``$filesize``, is ``1f40``, so
+the comparison that is done ends up being "1 < 4096".
+
+Logic
+~~~~~
+
+The ``!`` operator negates the sense of the test of the expression
+``<expr>``.
+
+The ``-o`` and ``-a`` operators perform logical OR and logical AND,
+respectively, of the two expressions.
+
+File existence
+~~~~~~~~~~~~~~
+
+Like ordinary shells, the ``-e`` operator can be used to test for
+existence of a file. However, the U-Boot version takes three
+arguments:
+
+- The interface (e.g. ``mmc``).
+- The device number, possibly including a partition specification.
+- The usual path argument, which is interpreted relative to the root
+  of the filesystem.
+
+Regular expressions
+~~~~~~~~~~~~~~~~~~~
+
+When ``CONFIG_REGEX`` is enabled, an additional operator ``=~`` is
+available. This is similar to the same operator available with bash's
+extended test command ``[[ ]]``. The left operand is a string which is
+matched against the regular expression described by the right operand.
+
+The regular expression engine supports these features:
+
+- Anchoring ``^`` and ``$``, matching at the beginning/end of the
+  string.
+- Matching any single character (including whitespace) using ``.``.
+- Character classes ``[ ]``, including ranges ``[0-9]`` and negation
+  ``[^ /.]``.
+- Grouping ``( )``.
+- Alternation ``|``.
+- Postfix qualifiers ``*``, ``+`` and ``?`` and their non-greedy
+  variants ``*?``, ``+?`` and ``??``
+
+For extracting the parts matching a capture group and/or performing
+substitutions, including back references, see :doc:`setexpr`.