113

Is there a way to make bash display stderr messages in red color?

  • 3
    I guess bash will never colorize its output: some program may want to parse something, and colorizing will spoil data with escaped sequences. A GUI app should handle colors, i guess. – kolypto Aug 26 '09 at 22:20
  • Combining Balázs Pozsár and killdash9 answer gives the crisp: function color { "$@" 2> >(sed $'s,.*,\e[31m&\e[m,') } Works for bash and zsh. Can't add this as an answer b/c reputation. – Heinrich Hartmann Sep 14 '18 at 19:38
  • I am waiting for an answer that modifies bash to do this. The solutions below all actually modify stderr and possibly even reorder it w.r.t. stdout which breaks things when the exact byte sequence of stderr must be preserved e.g. when piping. – masterxilo Sep 21 '18 at 9:06

11 Answers 11

93
command 2> >(while read line; do echo -e "\e[01;31m$line\e[0m" >&2; done)
  • 5
    Great! But i wonder if there's a way to make it permanent :) – kolypto Aug 26 '09 at 21:47
  • 7
    Great tip! Suggestion: By adding >&2 right before ; done), the output intended for stderr actually is written to stderr. That's helpful if you want to capture the normal output of the program. – henko Oct 31 '12 at 8:12
  • 8
    The following uses tput, and is slightly more readable in my opinion: command 2> >(while read line; do echo -e "$(tput setaf 1)$line$(tput sgr0)" >&2; done) – Stefan Lasiewski Feb 14 '13 at 21:59
  • 1
    I think executing 2 tput processes for each output line is not elegant at all. Maybe if you would store the output of the tput commands in a variable and use those for each echo. But then again, readability is not really better. – Balázs Pozsár Oct 7 '14 at 12:09
  • 1
    This solution does not preserve whitespace but I like it for its brevity. IFS= read -r line should help but doesn't. Not sure why. – Max Murphy Jul 1 '16 at 11:05
86

Method 1: Use process substitution:

command 2> >(sed $'s,.*,\e[31m&\e[m,'>&2)

Method 2: Create a function in a bash script:

color()(set -o pipefail;"$@" 2>&1>&3|sed $'s,.*,\e[31m&\e[m,'>&2)3>&1

Use it like this:

$ color command

Both methods will show the command's stderr in red.

Keep reading for an explanation of how method 2 works. There are some interesting features demonstrated by this command.

  • color()... — Creates a bash function called color.
  • set -o pipefail — This is a shell option that preserves the error return code of a command whose output is piped into another command. This is done in a subshell, which is created by the parentheses, so as not to change the pipefail option in the outer shell.
  • "$@" — Executes the arguments to the function as a new command. "$@" is equivalent to "$1" "$2" ...
  • 2>&1 — Redirects the stderr of the command to stdout so that it becomes sed's stdin.
  • >&3 — Shorthand for 1>&3, this redirects stdout to a new temporary file descriptor 3. 3 gets routed back into stdout later.
  • sed ... — Because of the redirects above, sed's stdin is the stderr of the executed command. Its function is to surround each line with color codes.
  • $'...' A bash construct that causes it to understand backslash-escaped characters
  • .* — Matches the entire line.
  • \e[31m — The ANSI escape sequence that causes the following characters to be red
  • & — The sed replace character that expands to the entire matched string (the entire line in this case).
  • \e[m — The ANSI escape sequence that resets the color.
  • >&2 — Shorthand for 1>&2, this redirects sed's stdout to stderr.
  • 3>&1 — Redirects the temporary file descriptor 3 back into stdout.
  • 9
    +1 best answer! absolutly underrated! – muhqu Sep 20 '13 at 11:27
  • 2
    Great answer and even better explanation – Daniel Serodio Oct 22 '14 at 19:56
  • Why do you need to do all the additional redirection? seems like overkill – qodeninja Apr 2 '15 at 15:16
  • @qodeninja The explanation gives the purpose for the redirection. If you can find a simpler way to do it, I'd love to see it! – killdash9 Apr 2 '15 at 16:44
  • 1
    Is there a way to make it work in zsh? – Eyal Levin Aug 25 '16 at 9:14
23

You can also check out stderred: https://github.com/sickill/stderred

  • Wow, this utility is great, the only thing that it would need is to have an apt repository that installs it for all users, with one line, not having to do more work to enable it. – sorin Apr 3 '12 at 14:17
  • Seemed to work well when I tested it with a build script in a separate terminal, but I'm hesitant to use it globally (in .bashrc). Thanks though! – Joel Purra Aug 24 '12 at 15:18
  • In OS X El Capitan, the way this works (DYLD_INSERT_LIBRARIES) is "broken" in system binaries because they are protected by SIP. So it might be better to use the bash options given in other answers. – hmijail Apr 22 '16 at 21:41
  • @hmijail for MacOS please follow github.com/sickill/stderred/issues/60 so we can find a workaround, a partial one already exists but is a little bit buggy. – sorin Jul 16 '18 at 7:57
14

http://sourceforge.net/projects/hilite/

12

The bash way of making stderr permanently red is using 'exec' to redirect streams. Add the following to your bashrc:

exec 9>&2
exec 8> >(
    while IFS='' read -r line || [ -n "$line" ]; do
       echo -e "\033[31m${line}\033[0m"
    done
)
function undirect(){ exec 2>&9; }
function redirect(){ exec 2>&8; }
trap "redirect;" DEBUG
PROMPT_COMMAND='undirect;'

I have posted on this previously: How to set font color for STDOUT and STDERR

  • related: unix.stackexchange.com/questions/367636/… – Blauhirn May 29 '17 at 3:59
  • This is the best answer by far; easy to implement without installation/requiring sudo privilege, and can be generalized to all commands. – Luke Davis Sep 26 '17 at 2:25
  • Unfortunately this doesn't play well with command chaining (command && nextCommand || errorHandlerCommand). The error output goes after errorHandlerCommand output. – carlin.scott Jun 18 '18 at 23:30
  • Similarly, if I source ~/.bashrc twice with this, my terminal basically locks up. – Dolph Sep 11 '18 at 20:11
  • @Dolf: In my bashrc I easily guard against this with a surrounding if statement to prevent this code from reloading. Otherwise, the problem is the redirection 'exec 9>&2' after redirection has already taken place. Perhaps change it to a constant if you know where >2 is pointing at originally. – gospes Oct 1 '18 at 8:48
7

I've made a wrapper script that implements Balázs Pozsár's answer in pure bash. Save it in your $PATH and prefix commands to colorize their output.


    #!/bin/bash

    if [ $1 == "--help" ] ; then
        echo "Executes a command and colorizes all errors occured"
        echo "Example: `basename ${0}` wget ..."
        echo "(c) o_O Tync, ICQ# 1227-700, Enjoy!"
        exit 0
        fi

    # Temp file to catch all errors
    TMP_ERRS=$(mktemp)

    # Execute command
    "$@" 2> >(while read line; do echo -e "\e[01;31m$line\e[0m" | tee --append $TMP_ERRS; done)
    EXIT_CODE=$?

    # Display all errors again
    if [ -s "$TMP_ERRS" ] ; then
        echo -e "\n\n\n\e[01;31m === ERRORS === \e[0m"
        cat $TMP_ERRS
        fi
    rm -f $TMP_ERRS

    # Finish
    exit $EXIT_CODE

  • 2
    This could be made more efficient if "|tee..." was put after "done". – Juliano Aug 27 '09 at 1:27
3

You can use a function like this


 #!/bin/sh

color() {
      printf '\033[%sm%s\033[m\n' "$@"
      # usage color "31;5" "string"
      # 0 default
      # 5 blink, 1 strong, 4 underlined
      # fg: 31 red,  32 green, 33 yellow, 34 blue, 35 purple, 36 cyan, 37 white
      # bg: 40 black, 41 red, 44 blue, 45 purple
      }
string="Hello world!"
color '31;1' "$string" >&2

I append >&2 to print to stderr

  • 4
    Not addressing the problem. You haven't provided a way of separating stderr from stdout, which is what the O.P. is interested in. – Jeremy Visser Aug 27 '09 at 1:54
1

I have a slightly modified version of O_o Tync's script. I needed to make these mods for OS X Lion and it's not perfect because the script sometimes completes before the wrapped command does. I've added a sleep but I'm sure there's a better way.

#!/bin/bash

   if [ $1 == "--help" ] ; then
       echo "Executes a command and colorizes all errors occured"
       echo "Example: `basename ${0}` wget ..."
       echo "(c) o_O Tync, ICQ# 1227-700, Enjoy!"
       exit 0
       fi

   # Temp file to catch all errors
   TMP_ERRS=`mktemp /tmp/temperr.XXXXXX` || exit 1

   # Execute command
   "$@" 2> >(while read line; do echo -e "$(tput setaf 1)$line\n" | tee -a $TMP_ERRS; done)
   EXIT_CODE=$?

   sleep 1
   # Display all errors again
   if [ -s "$TMP_ERRS" ] ; then
       echo -e "\n\n\n$(tput setaf 1) === ERRORS === "
       cat $TMP_ERRS
   else
       echo "No errors collected in $TMP_ERRS"
   fi
   rm -f $TMP_ERRS

   # Finish
   exit $EXIT_CODE
1

This solution worked for me: https://superuser.com/questions/28869/immediately-tell-which-output-was-sent-to-stderr

I've put this function in my .bashrc or .zshrc:

# Red STDERR
# rse <command string>
function rse()
{
    # We need to wrap each phrase of the command in quotes to preserve arguments that contain whitespace
    # Execute the command, swap STDOUT and STDERR, colour STDOUT, swap back
    ((eval $(for phrase in "$@"; do echo -n "'$phrase' "; done)) 3>&1 1>&2 2>&3 | sed -e "s/^\(.*\)$/$(echo -en \\033)[31;1m\1$(echo -en \\033)[0m/") 3>&1 1>&2 2>&3
}

Then for example:

$ rse cat non_existing_file.txt

will give me a red output.

1

using xargs and printf:

command 2> >(xargs -0 printf "\e[31m%s\e[m" >&2)
0

a version using fifos

mkfifo errs
stdbuf -o0 -e0 -i0 grep . foo | while read line; do echo -e "\e[01;31m$line  \e[0m" >&2; done &
stdbuf -o0 -e0 -i0 sh $script 2>errs

protected by Sven Aug 23 '18 at 14:37

Thank you for your interest in this question. Because it has attracted low-quality or spam answers that had to be removed, posting an answer now requires 10 reputation on this site (the association bonus does not count).

Would you like to answer one of these unanswered questions instead?

Not the answer you're looking for? Browse other questions tagged or ask your own question.