4 coloredstderr is a small library which uses 'LD_PRELOAD' to color stderr. It
5 ``follows'' dups, has minimal performance overhead and can ignore certain
8 Like all solutions using 'LD_PRELOAD' it only works with dynamically linked
9 binaries. Statically linked binaries, for example valgrind, are not supported.
10 setuid binaries are also not supported ('LD_PRELOAD' disabled for security
13 It was inspired by stderred [2]. Similar solutions (using 'LD_PRELOAD')
16 - stderred [1], but doesn't `follow' dups (I somehow missed it when looking
17 for existing implementations)
18 - stderred [2], but only hooks `write()`
20 [1]: https://github.com/sickill/stderred
21 [2]: https://github.com/trapd00r/stderred
23 Most other existing solutions use a second process which colors its input and
24 pipe stderr to it. However this creates different runtime behaviour resulting
25 in a different ordering of the output. Partial lines (no newline) also often
26 cause problems. coloredstderr handles these cases correctly (but has other
27 possible issues, see below).
29 coloredstderr is licensed under GPL 3 (or later).
35 - C99 compiler (variable length arrays)
36 - dynamic linker/loader which supports 'LD_PRELOAD' (e.g. GNU/Linux's or
43 If you're using the Git version, run `autoreconf -fsi` first to generate
46 ./configure && make && make check
48 Then either install the library with `make install` or just copy it from
49 `src/.libs/` to wherever you want to install it:
51 rm -f /destination/path/for/library/libcoloredstderr.so
52 cp -L src/.libs/libcoloredstderr.so /destination/path/for/library/
54 *Important:* If you install `libcoloredstderr.so` manually, make sure _not_ to
55 use plain `cp` to overwrite an existing `libcoloredstderr.so` file which is in
56 use! Doing so will crash most processes which were started with 'LD_PRELOAD'
57 set to this file. This is not a bug in coloredstderr, but a general problem.
58 `cp` truncates the file which causes the `mmap()` ed library to be in an
59 inconsistent state causing a segmentation fault when using any functions of
60 the library. Just remove the file first and then copy it. `make install`
61 handles the install in this way and is therefore not affected.
63 As a simple safeguard, `make` builds and installs the `libcoloredstderr.so`
64 file non-writable to prevent accidental overwrites. Even if the overwrite is
65 forced with `cp -f`, the file is unlinked and recreated by `cp` because the
66 file is non-writable, preventing the problem.
72 Set 'LD_PRELOAD' to include the _absolute_ path to `libcoloredstderr.so`:
74 LD_PRELOAD=/absolute/path/to/libcoloredstderr.so
76 The 'COLORED_STDERR_FDS' environment variable must be set to the file
77 descriptors which should be colored (comma separated list). Normally this is
82 The trailing comma is important!
85 A default setup could look like this:
87 LD_PRELOAD="$HOME/bin/libcoloredstderr.so"
89 export LD_PRELOAD COLORED_STDERR_FDS
92 The following additional environment variables are available:
94 - 'COLORED_STDERR_PRE'
95 String to write before each write to stderr, defaults to "\033[31m" (red).
96 - 'COLORED_STDERR_POST'
97 String to write after each write to stderr, defaults to "\033[0m" (reset
99 - 'COLORED_STDERR_FORCE_WRITE'
100 If set to an non-empty value add pre/post strings even when not writing to a
101 terminal, e.g. when writing to a file. By default, only writes to a terminal
103 - 'COLORED_STDERR_IGNORED_BINARIES'
104 Comma separated list of binary names/paths which should not be tracked
105 (including their children). Useful for `reset` which writes to the terminal,
106 but fails to work if the output is colored. See below for an example.
107 Requires `/proc/self/exe`.
109 All environment variables starting with 'COLORED_STDERR_PRIVATE_*' are
110 internal variables used by the implementation and should not be set manually.
111 See the source for details.
114 To set custom colors as pre/post strings you can use the `$''` feature of Bash
117 export COLORED_STDERR_PRE=$'\033[91m' # bright red
118 export COLORED_STDERR_POST=$'\033[0m' # default
120 Or to be more compatible you can use the following which should work in any
124 COLORED_STDERR_PRE="${esc}[91m" # bright red
125 COLORED_STDERR_POST="${esc}[0m" # default
126 export COLORED_STDERR_PRE COLORED_STDERR_POST
128 Fix `reset`; its writes to the terminal must be unaltered. `reset` is a
129 symbolic-link to `tset` on some systems, adapt as necessary:
131 COLORED_STDERR_IGNORED_BINARIES=/usr/bin/tset
132 export COLORED_STDERR_IGNORED_BINARIES
138 To enable debug mode, configure coloredstderr with '--enable-debug'.
140 *Important:* Debug mode enables `assert()`s in the code which might abort the
141 process using 'LD_PRELOAD' if an error condition is detected!
143 Debug mode is slower than normal mode. To log only warnings without the
144 overhead of debug mode use '--enable-warnings'. `assert()`s are not enabled
145 with '--enable-warnings', so it's safe to use.
147 Debug messages are appended to the file `colored_stderr_debug_log.txt` in the
148 current working directory _if_ it exists. Be careful, this file might grow
151 *Important:* Warnings are written to `$HOME/colored_stderr_warning_log.txt`
152 even if it _does not_ exist (only if debug or warning mode is enabled)! If it
153 doesn't exist it's created. An existing file isn't overwritten, but the
154 warnings are appended at the end.
160 - `{fputc,putc,putchar}_unlocked()` are not hooked with glibc when writing to
161 stdout (which might be redirected to stderr). Can't be fixed as the compiler
162 inlines the code into the program without calling any function.
163 - Test `test_stdio.sh` fails on FreeBSD, because FreeBSD does handle the above
164 correctly (no inlining), but the test is designed for GNU/Linux.
165 - 'COLORED_STDERR_IGNORED_BINARIES' requires `/proc/self/exe`. Suggestions
167 - Output of `strace` is not always colored correctly as the output from
168 `coloredstderr` is traced and displayed as well. Suggestions welcome.
174 If you find any bugs not mentioned in this document please report them to
175 <simon@ruderich.org> with coloredstderr in the subject.
181 Written by Simon Ruderich <simon@ruderich.org>.
187 coloredstderr is licensed under GPL version 3 or later.
189 Copyright (C) 2013-2014 Simon Ruderich
191 This program is free software: you can redistribute it and/or modify
192 it under the terms of the GNU General Public License as published by
193 the Free Software Foundation, either version 3 of the License, or
194 (at your option) any later version.
196 This program is distributed in the hope that it will be useful,
197 but WITHOUT ANY WARRANTY; without even the implied warranty of
198 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
199 GNU General Public License for more details.
201 You should have received a copy of the GNU General Public License
202 along with this program. If not, see <http://www.gnu.org/licenses/>.