Re: [Help-bash] Question: Capturing command output (on-screen keyword colorizer/prettifier).

[Pierre Gaston]

On Wed, Oct 5, 2016 at 4:20 AM, Matthew Giassa <address@hidden> wrote:

>
> Good day,
>
>         I'm working on a means of assisting some testers with unit testing
> some
> scripts and applications they wrote. I'm using LD_PRELOAD to hook the
> output
> functions used by BASh so that each line can be analyzed, and if a
> specific
> keyword (ERROR_CUSTOM_DB, NOTE_CUSTOM_DB_APP, etc) is detected, it
> modifies the
> output stream by putting in BASh-specific color codes so that the text
> is
> obvious on-screen.
>
>         Obviously, the task can be automated via `grep`, but the tool
> operates
> only in an interactive mode, so a person needs to be present to manually
> make
> decisions with respect to program flow (can't be automated in a trivial
> manner).
> Additionally, the tools under test cannot be modified, and we are not
> allowed
> to use modify .bashrc. Hence, my LD_PRELOAD efforts to make certain
> error
> codes more obvious.
>
>         I've hooked the following functions so far, and have implemented a
> linker version script and logging functions to confirm they are being
> used.
> * __printf_chk
> * __fprintf_chk
> * __vfprintf_chk
> * write
> * fwrite
>
>         While I'm able to get the output of echo commands, the PS1/PS2/etc
> variables, and so on, I can't seem to get the output of the "ls" command
> for
> example. I've checked the symbols used to write data out to the console
> via the
> following: readelf --dyn-syms /bin/bash | grep -i -e write -e printf
>
> Output:
>      6: 0000000000000000     0 FUNC    GLOBAL DEFAULT  UND
> address@hidden (5)
>     13: 0000000000000000     0 FUNC    GLOBAL DEFAULT  UND
> address@hidden (5)
>     39: 0000000000000000     0 FUNC    GLOBAL DEFAULT  UND
> address@hidden (2)
>     98: 0000000000000000     0 FUNC    GLOBAL DEFAULT  UND
> address@hidden (8)
>    142: 0000000000000000     0 FUNC    GLOBAL DEFAULT  UND
> address@hidden (5)
>    152: 0000000000000000     0 FUNC    GLOBAL DEFAULT  UND
> address@hidden (5)
>    191: 0000000000000000     0 FUNC    GLOBAL DEFAULT  UND
> address@hidden (2)
>    192: 0000000000000000     0 FUNC    GLOBAL DEFAULT  UND
> address@hidden (5)
>    213: 0000000000000000     0 FUNC    GLOBAL DEFAULT  UND
> address@hidden (5)
>
>         So as far as I can see, I'm hooking all of the typical commands
> BASh
> would use to write to the console, yet there is still output which I'm
> not
> capturing.
>
>         Is there yet another function BASh uses which I would need to hook
> in
> order to capture all command output within the LD_PRELOAD'ed C library?
>
> Thank you.
>
>
>
> ============================================================
> Matthew Giassa, MASc, BASc, EIT
> Security and Embedded Systems Specialist
> linkedin: https://ca.linkedin.com/in/giassa
> e-mail:   address@hidden
> website:  www.giassa.net
>
>
> Could it be that your problem is that "ls" like many typical command is an
external executable that bash runs and not a bash builtin?
external commands write directly to the terminal.