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Re: [Help-bash] Why`trap DEBUG` has no effect if it is called inside a f

From: Peng Yu
Subject: Re: [Help-bash] Why`trap DEBUG` has no effect if it is called inside a function?
Date: Wed, 22 Apr 2015 22:48:01 -0500

On Wed, Apr 22, 2015 at 9:25 PM, Chet Ramey <address@hidden> wrote:
> On 4/21/15 11:53 PM, Peng Yu wrote:
>>> The DEBUG trap is not inherited (set to the default) and restored to its
>>> previous value unless the `functrace' option is set:
>> For `set -o functrace` or `set -T`, the following example shows that
>> commands inside functions inherit the same DEBUG trap as the
>> functions. But why 'f' is printed twice after `set -T`.
> When a shell function is executed, the DEBUG trap is run at function entry,
> so debuggers can trap when the function is executed, rather than just
> before the first command in the function body.  At that point, BASH_COMMAND
> is still `f'.
>> For `declare -t`, I don't see there is any difference. Do I use
>> `declare -t` correctly?
> Unless you use `-f', each name argument to declare is interpreted as a
> shell variable.
>> The following example shows that I am able to set the signal for DEBUG
>> within a function so that the signal will be able outside the
>> function. Isn't it logical to allow the reset of the signal in the
>> similar way so that DEBUG signal outside the function will also be
>> reset?
> The same explanation applies.  It seems reasonable to make the same
> change for function execution.

So we should expect this bug or "feature" will be fixed in the next
version of bash?

>> Also the man page says "extdebug...  5. Function  tracing  is enabled:
>>  command substitution, shell functions, and subshells invoked with (
>> command ) inherit the DEBUG and RETURN traps." The following example
>> shows no difference on whether extdebug is enabled or not. Why
>> functions in `f` are not trapped with the command set for DEBUG at the
>> beginning of the script?
> Bad documentation; it's never done that.  Maybe it should.
> --
> ``The lyf so short, the craft so long to lerne.'' - Chaucer
>                  ``Ars longa, vita brevis'' - Hippocrates
> Chet Ramey, ITS, CWRU    address@hidden


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