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diff --git a/doc/gawk.texi b/doc/gawk.texi index 445ef9c1..4928769d 100644 --- a/doc/gawk.texi +++ b/doc/gawk.texi @@ -30172,17 +30172,16 @@ a number of translations for its messages. @cindex debugging @command{awk} programs @c The original text for this chapter was contributed by Efraim Yawitz. -@c FIXME: Add more indexing. It would be nice if computer programs worked perfectly the first time they were run, but in real life, this rarely happens for programs of any complexity. Thus, most programming languages have facilities available -for ``debugging'' programs, and now @command{awk} is no exception. +for ``debugging'' programs, and @command{awk} is no exception. The @command{gawk} debugger is purposely modeled after @uref{https://www.gnu.org/software/gdb/, the GNU Debugger (GDB)} command-line debugger. If you are familiar with GDB, learning -how to use @command{gawk} for debugging your program is easy. +how to use @command{gawk} for debugging your programs is easy. @menu * Debugging:: Introduction to @command{gawk} debugger. @@ -30218,6 +30217,7 @@ In that case, what can you expect from such a tool? The answer to that depends on the language being debugged, but in general, you can expect at least the following: +@cindex debugger capabilities @itemize @value{BULLET} @item The ability to watch a program execute its instructions one by one, @@ -30250,13 +30250,15 @@ functional program that you or someone else wrote). @node Debugging Terms @subsection Debugging Concepts +@cindex debugger concepts Before diving in to the details, we need to introduce several important concepts that apply to just about all debuggers. The following list defines terms used throughout the rest of this @value{CHAPTER}: @table @dfn -@cindex stack frame +@cindex call stack (debugger) +@cindex stack frame (debugger) @item Stack frame Programs generally call functions during the course of their execution. One function can call another, or a function can call itself (recursion). @@ -30278,7 +30280,7 @@ invoked. Commands that print the call stack print information about each stack frame (as detailed later on). @item Breakpoint -@cindex breakpoint +@cindex breakpoint (debugger) During debugging, you often wish to let the program run until it reaches a certain point, and then continue execution from there one statement (or instruction) at a time. The way to do this is to set @@ -30288,7 +30290,7 @@ take over control of the program's execution. You can add and remove as many breakpoints as you like. @item Watchpoint -@cindex watchpoint +@cindex watchpoint (debugger) A watchpoint is similar to a breakpoint. The difference is that breakpoints are oriented around the code: stop when a certain point in the code is reached. A watchpoint, however, specifies that program execution @@ -30316,15 +30318,19 @@ In addition, because @command{awk} is by design a very concise language, it is easy to lose sight of everything that is going on ``inside'' each line of @command{awk} code. The debugger provides the opportunity to look at the individual primitive instructions carried out -by the higher-level @command{awk} commands. +by the higher-level @command{awk} commands.@footnote{The ``primitive +instructions'' are defined by @command{gawk} itself; the debugger +does not work at the level of machine instructions.} @node Sample Debugging Session @section Sample @command{gawk} Debugging Session @cindex sample debugging session +@cindex example debugging session +@cindex debugging, example session In order to illustrate the use of @command{gawk} as a debugger, let's look at a sample debugging session. We will use the @command{awk} implementation of the -POSIX @command{uniq} command described earlier (@pxref{Uniq Program}) +POSIX @command{uniq} command presented earlier (@pxref{Uniq Program}) as our example. @menu @@ -30358,6 +30364,7 @@ in the command line to the debugger rather than as part of the @code{run} command at the debugger prompt.) The @option{-1} is an option to @file{uniq.awk}. +@cindex debugger, prompt Instead of immediately running the program on @file{inputfile}, as @command{gawk} would ordinarily do, the debugger merely loads all the program source files, compiles them internally, and then gives @@ -30375,7 +30382,7 @@ code has been executed. @subsection Finding the Bug Let's say that we are having a problem using (a faulty version of) -@file{uniq.awk} in the ``field-skipping'' mode, and it doesn't seem to be +@file{uniq.awk} in ``field-skipping'' mode, and it doesn't seem to be catching lines which should be identical when skipping the first field, such as: @@ -30407,6 +30414,10 @@ a breakpoint in @file{uniq.awk} is at the beginning of the function @code{are_equal()}, which compares the current line with the previous one. To set the breakpoint, use the @code{b} (breakpoint) command: +@cindex debugger, setting a breakpoint +@cindex debugger, @code{breakpoint} command +@cindex debugger, @code{break} command +@cindex debugger, @code{b} command @example gawk> @kbd{b are_equal} @print{} Breakpoint 1 set at file `awklib/eg/prog/uniq.awk', line 63 @@ -30416,6 +30427,8 @@ The debugger tells us the file and line number where the breakpoint is. Now type @samp{r} or @samp{run} and the program runs until it hits the breakpoint for the first time: +@cindex debugger, running the program +@cindex debugger, @code{run} command @example gawk> @kbd{r} @print{} Starting program: @@ -30431,6 +30444,9 @@ let's see how we got to where we are. At the prompt, we type @samp{bt} (short for ``backtrace''), and the debugger responds with a listing of the current stack frames: +@cindex debugger, show stack frames +@cindex debugger, @code{bt} command +@cindex debugger, @code{backtrace} command @example gawk> @kbd{bt} @print{} #0 are_equal(n, m, clast, cline, alast, aline) @@ -30450,6 +30466,8 @@ of some variables. Let's say we type @samp{p n} @code{n}, a parameter to @code{are_equal()}. Actually, the debugger gives us: +@cindex debugger, @code{print} command +@cindex debugger, @code{p} command @example gawk> @kbd{p n} @print{} n = untyped variable @@ -30500,6 +30518,8 @@ be inside this function. To investigate further, we must begin ``stepping through'' the lines of @code{are_equal()}. We start by typing @samp{n} (for ``next''): +@cindex debugger, @code{n} command +@cindex debugger, @code{next} command @example @group gawk> @kbd{n} @@ -30545,6 +30565,7 @@ This information is useful enough (we now know that none of the words were accidentally left out), but what if we want to see inside the array? +@cindex debugger, printing single array elements The first choice would be to use subscripts: @example @@ -30564,6 +30585,7 @@ This would be kind of slow for a 100-member array, though, so @command{gawk} provides a shortcut (reminiscent of another language not to be mentioned): +@cindex debugger, printing all array elements @example gawk> @kbd{p @@alast} @print{} alast["1"] = "awk" @@ -30643,6 +30665,7 @@ Getting information Miscellaneous @end itemize +@cindex debugger, repeating commands Each of these are discussed in the following subsections. In the following descriptions, commands that may be abbreviated show the abbreviation on a second description line. @@ -31229,9 +31252,11 @@ Options are read back into the next session upon startup. @item @code{trace} [@code{on} | @code{off}] @cindex instruction tracing, in debugger +@cindex debugger, instruction tracing Turn instruction tracing on or off. The default is @code{off}. @end table +@cindex debugger, save commands to a file @item @code{save} @var{filename} Save the commands from the current session to the given @value{FN}, so that they can be replayed using the @command{source} command. @@ -31404,7 +31429,9 @@ fairly self-explanatory, and using @code{stepi} and @code{nexti} while @node Readline Support @section Readline Support @cindex command completion, in debugger +@cindex debugger, command completion @cindex history expansion, in debugger +@cindex debugger, history expansion If @command{gawk} is compiled with @uref{http://cnswww.cns.cwru.edu/php/chet/readline/readline.html, @@ -31443,6 +31470,7 @@ and @node Limitations @section Limitations +@cindex debugger, limitations We hope you find the @command{gawk} debugger useful and enjoyable to work with, but as with any program, especially in its early releases, it still has some limitations. A few that it's worth being aware of are: |