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stderr in red
C CMake Makefile Shell
Latest commit dfe65c8 @cehoffman cehoffman It is possible to have err/warn and no errc/warnc
This caused a few reported core dumps because err would try to call
a null function pointer for verrc on Linux. This fixes #26.


stderr in red.


stderred hooks on write() and a family of stream functions (fwrite, fprintf, error...) from libc in order to colorize all stderr output that goes to terminal thus making it distinguishable from stdout. Basically it wraps text that goes to file with descriptor "2" with proper ANSI escape codes making text red.

It's implemented as a shared library and doesn't require recompilation of existing binaries thanks to preload/insert feature of dynamic linkers.

It's supported on Linux (with LD_PRELOAD), FreeBSD (also LD_PRELOAD) and OSX (with DYLD_INSERT_LIBRARIES).

Watch this intro asciicast to see it in action.


Clone this repository:

$ git clone git://
$ cd stderred

Important: In all cases below make sure that path to is absolute!

Linux and FreeBSD

Make sure you have cmake and the gcc toolchain required for compilation installed:

# Ubuntu
sudo apt-get install build-essential cmake

# Fedora
sudo yum install make cmake gcc gcc-c++

# FreeBSD
pkg install cmake


$ make

Export LD_PRELOAD variable in your shell's config file by putting following in your .bashrc/.zshrc:

export LD_PRELOAD="/absolute/path/to/stderred/build/${LD_PRELOAD:+:$LD_PRELOAD}"

Multi-arch Linux and FreeBSD

On some Linux distros you can install 32-bit packages on 64-bit system. Shared libraries compiled for 64-bit doesn't work with 32-bit binaries though. It happens that 64-bit binaries call 32-bit ones resulting in warning message printed to terminal about not compatible LD_PRELOAD shared lib.

Fortunately Linux's dynamic linker has a feature called Dynamic String Token (DST). It allows dynamic substitution of $LIB token in LD_PRELOAD variable with "lib" or "lib64" respectively for 32 and 64-bit binaries when the binary is being run. Thanks to that you can compile stderred for both architectures and automatically use proper version of this shared library.

On 64-bit Fedora, for example, you need to install libc development headers for both architectures:

$ sudo yum install glibc-devel.i686 glibc-devel.x86_64

compile it like this:

$ make 32 && make 64

and export LD_PRELOAD like this in your shell's config:

export LD_PRELOAD="/path/to/stderred/\$LIB/${LD_PRELOAD:+:$LD_PRELOAD}"

* Note that there is no support for $LIB token on Ubuntu.


$ make

Export DYLD_INSERT_LIBRARIES variable in your shell's config file by putting following in your .bashrc/.zshrc:

export DYLD_INSERT_LIBRARIES="/absolute/path/to/build/libstderred.dylib${DYLD_INSERT_LIBRARIES:+:$DYLD_INSERT_LIBRARIES}"

Universal lib on OSX

OSX solves multi-arch problem (described above in "Multi-arch Linux and FreeBSD") by supporting so called "universal" libraries that include 2 copies of code compiled for both 32 and 64-bit architecture in the single library file.

If you feel you will want universal library then build it this way:

$ make universal

and export shell env like above.

Checking if it works

$ find -q
$ cat nonexistingfile
$ ls nonexistingfile
$ python -c 'import os; print "Yo!"; os.write(2, "Jola\n\r")'
$ STDERRED_ESC_CODE=$(echo -e '\e[;92m') ruby -e 'puts "Yo!"; warn "Jola"'

Jola should be in a red and green dress.

stderred in action

Alternative way: aliasing

Alternative to enabling it globally via shell config is to create alias and use it to selectively colorize stderr for the commands you run:

$ alias stderred="LD_PRELOAD=/absolute/path/to/build/\${LD_PRELOAD:+:\$LD_PRELOAD}"
$ stderred java lol


Custom color code

If you prefer other color or you want to use additional escape codes (for bold/bright, italic, different background) you can export STDERRED_ESC_CODE with desired escape code sequence.

Here's an example for bold red:

bold=$(tput bold || tput md)
red=$(tput setaf 1)
export STDERRED_ESC_CODE=`echo -e "$bold$red"`

Program Blacklisting

Some programs abuse stderr and print stuff on it even when they really shouldn't. If you want to turn off stderred for particular programs you can export STDERRED_BLACKLIST with a desired POSIX Extended Regular Expression matching names of these programs.

Here's an example that will blacklist bash, and all programs with names starting with "test":

export STDERRED_BLACKLIST="^(bash|test.*)$"

Alternative implementations

Simpler and much less reliable solution when using Zsh is to use named pipes trick proposed on Gentoo Linux wiki. It has some race condition/buffering issues and breaks on interactive commands writing to stderr though.


Current implementation:

Original concept and initial implementation:

  • Asheesh Laroia


You are free to use this program under the terms of the license found in LICENSE file.

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