For nearly all commands in U-Boot the '?' variable is handled the same
way with 0 meaning success, 1 meaning any failure.  Explain this in the
general rules section of the cmdline documentation (with a link to a
counter example) and then remove the redundant wording from most
commands. We retain a section about the return value in a number of
places where we are doing something such as always returning a specific
value or we have useful additional information to go along with the
normal return codes.

Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>

Add documentation for the test command, including the newly added =~
operator and some gotchas wrt. the numeric comparisons.

Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Rasmus Villemoes <ravi@prevas.dk>

In gsub, when the destination string is empty, the string 't' is
provided and the regular expression doesn't match, then the final result
is an empty string.

Example:

=> echo ${foo}

=> setenv foo
=> setexpr foo gsub e a bar
=> echo ${foo}

=>

The variable ${foo} should contain "bar" and the lack of match shouldn't
be considered an error.

This patch fixes the erroneous behavior by removing the return
statement and breaking out of the loop in case of lack of match.

Also add a test for the no match case.

Signed-off-by: Massimiliano Minella <massimiliano.minella@se.com>

Add the description of CLI commands to the generated index.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>

Add missing information to the configuration section of the setexpr
man-page.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

Currently all shell command docs are put in the doc/usage root.
Let's group them into cmd/ sub-directory.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>