README
======

coloredstderr is a small library which uses 'LD_PRELOAD' to color stderr.


Like all solutions using 'LD_PRELOAD' it only works with dynamically linked
binaries. Statically linked binaries, for example valgrind, are not supported.


It was inspired by stderred [2]. Similar solutions (using 'LD_PRELOAD')
include:

- stderred [1], but doesn't `follow' dups (I somehow missed it when looking
  for existing implementations)
- stderred [2], but only hooks `write()`

[1]: https://github.com/sickill/stderred
[2]: https://github.com/trapd00r/stderred

Most other existing solutions use a second process which colors its input and
pipe stderr to it. However this creates different runtime behaviour resulting
in a different ordering of the output. Partial lines (no newline) also often
cause problems.


DEPENDENCIES
------------

- C99 compiler (variable length arrays)
- dynamic linker/loader which supports 'LD_PRELOAD' (e.g. GNU/Linux's ld.so)


USAGE
-----

Set 'LD_PRELOAD' to include the _absolute_ path to `libcoloredstderr.so`:

    LD_PRELOAD=/absolute/path/to/libcoloredstderr.so

The 'COLORED_STDERR_FDS' environment variable must be set to the file
descriptors which should be colored (comma separated list). Normally this is
just 2 (stderr):

    COLORED_STDERR_FDS=2,

The trailing comma is important!


A default setup could look like this:

    LD_PRELOAD="$HOME/bin/libcoloredstderr.so"
    COLORED_STDERR_FDS=2,
    export LD_PRELOAD COLORED_STDERR_FDS


The following additional environment variables are available:

- 'COLORED_STDERR_PRE'
  String to write before each write to stderr, defaults to "\033[91m" (bright
  red).
- 'COLORED_STDERR_POST'
  String to write after each write to stderr, defaults to "\033[0m" (reset
  color).
- 'COLORED_STDERR_FORCE_WRITE'
  If set to an non-empty value add pre/post strings even when not writing to a
  terminal, e.g. when writing to a file. By default, only writes to a terminal
  are colored.


DEBUG
-----

To enable debug mode, configure coloredstderr with '--enable-debug'.

*Important:* Debug mode enables `assert()`s in the code which might abort the
process if an error condition is detected!

Debug mode is slower than normal mode. To log only warnings without the
overhead of debug mode use '--enable-warnings'. `assert()`s are not enabled
with '--enable-warnings', so it's safe to use.

Debug messages are written to the file `colored_stderr_debug_log.txt` in the
current working directory _if_ it exists. If it exists debug messages are
appended. Be careful, this file might grow very quickly.

*Important:* Warnings are written to `$HOME/colored_stderr_warning_log.txt`
even if it _does not_ exist (only if debug or warning mode is enabled)! If it
doesn't exist it's created. An existing file isn't overwritten, but the
warnings are appended at the end.


BUGS
----

If you find any bugs not mentioned in this document please report them to
<simon@ruderich.org> with coloredstderr in the subject.


AUTHORS
-------

Written by Simon Ruderich <simon@ruderich.org>.


LICENSE
-------

coloredstderr is licensed under GPL version 3 or later.

Copyright (C) 2013  Simon Ruderich

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program.  If not, see <http://www.gnu.org/licenses/>.