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Refine the 'define' documentation

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A while ago, an AdaCore user reported some difficulties with the
'define' command.  While some of these difficulties are intrinsic, or
at least difficult to change, it seemed sensible to document a couple
of the typical problems -- and to make the text describing argument
substitution a bit more prominent.

Approved-By: Eli Zaretskii <eliz@gnu.org>
This commit is contained in:
Tom Tromey
2024-07-23 10:01:39 -06:00
parent 5a2f7d248a
commit fa8c46f5ad
1 changed files with 16 additions and 6 deletions
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22
gdb/doc/gdb.texinfo
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@@ -29228,9 +29228,21 @@ files.
@cindex arguments, to user-defined commands
A @dfn{user-defined command} is a sequence of @value{GDBN} commands to
which you assign a new name as a command. This is done with the
@code{define} command. User commands may accept an unlimited number of arguments
separated by whitespace. Arguments are accessed within the user command
via @code{$arg0@dots{}$argN}. A trivial example:
@code{define} command.
User commands may accept an unlimited number of arguments separated by
whitespace. Arguments are accessed within the user command via
@code{$arg0@dots{}$argN}. The arguments are text substitutions, so
they may reference variables, use complex expressions, or even perform
inferior functions calls. Note, however, that this textual
substitution means that working with certain arguments is difficult.
For example, there is no way for the user to pass an argument
containing a space; and while stringifying an argument can be done
using an expression like @code{"$arg1"}, this will fail if the
argument contains a quote. For more complicated and robust commands,
we recommend writing them in Python; see @ref{CLI Commands In Python}.
A trivial example:
@smallexample
define adder
@@ -29247,9 +29259,7 @@ adder 1 2 3
@noindent
This defines the command @code{adder}, which prints the sum of
its three arguments. Note the arguments are text substitutions, so they may
reference variables, use complex expressions, or even perform inferior
functions calls.
its three arguments.
@cindex argument count in user-defined commands
@cindex how many arguments (user-defined commands)