312

I'd like to be able to tail the output of a server log file that has messages like:

INFO
SEVERE

etc, and if it's SEVERE, show the line in red; if it's INFO, in green. What kind of alias can I setup for a tail command that would help me do this?

1

23 Answers 23

270

Try out multitail¹. This is an übergeneralization of tail -f. You can watch multiple files in separate windows, highlight lines based on their content, and more.

multitail -c /path/to/log

The colors are configurable. If the default color scheme doesn't work for you, write your own in the config file. For example, call multitail -cS amir_log /path/to/log with the following ~/.multitailrc:

colorscheme:amir_log
cs_re:green:INFO
cs_re:red:SEVERE

Another solution, if you're on a server where it's inconvenient to install non-standard tools, is to combine tail -f with sed or awk to add color selection control sequences. This requires tail -f to flush its standard output without delay even when its standard output is a pipe, I don't know if all implementations do this.

tail -f /path/to/log | awk '
  /INFO/ {print "\033[32m" $0 "\033[39m"}
  /SEVERE/ {print "\033[31m" $0 "\033[39m"}
'

or with sed

tail -f /path/to/log | sed --unbuffered \
    -e 's/\(.*INFO.*\)/\o033[32m\1\o033[39m/' \
    -e 's/\(.*SEVERE.*\)/\o033[31m\1\o033[39m/'

If your sed isn't GNU sed, replace \o033 by a literal escape character and remove --unbuffered.

Yet another possibility is to run tail -f in an Emacs shell buffer and use Emacs's syntax coloring abilities.

¹ The historical website vanished in early 2021. The latest version is still available in many distributions, e.g. Arch, Debian.

15
  • how can you do this with sed? (sorry for being lazy and not figuring it out myself!) But would you please add a sed example as well.
    – Ali
    Nov 28, 2011 at 16:41
  • 6
    @Ali Sed is less convenient because it doesn't have a syntax for the escape character, you need to have it literally in the script or use a shell quoting method to work it in. I recommend that you use awk. Nov 28, 2011 at 17:18
  • 9
    @Gilles In your tail -f with awk code, if a string doesn't have INFO and SEVERE, the string isn't be printed. How can I print the remain strings either? (The string doesn't need to be colored)
    – Benjamin
    Jun 29, 2012 at 10:32
  • 8
    @Benjamin Add ; next before the closing braces to skip further processing, and a new processing line 1 {print} at the end (1 means always). Jun 29, 2012 at 11:58
  • 6
    sed --unbuffered -e 's/\(.*FATAL.*\)/\o033[1;31m\1\o033[0;39m/' -e 's/\(.*ERROR.*\)/\o033[31m\1\o033[39m/' -e 's/\(.*WARN.*\)/\o033[33m\1\o033[39m/' -e 's/\(.*INFO.*\)/\o033[32m\1\o033[39m/' -e 's/\(.*DEBUG.*\)/\o033[34m\1\o033[39m/' -e 's/\(.*TRACE.*\)/\o033[30m\1\o033[39m/' -e 's/\(.*[Ee]xception.*\)/\o033[1;39m\1\o033[0;39m/' Sep 7, 2018 at 15:07
154

grc, the generic colourizer is pretty cool.

apt-get install grc

Just do

grc tail -f /var/log/apache2/error.log

and enjoy!

You’ll also find it on GitHub.

12
  • 4
    This is exactly what I needed: lightweight and simple. The coloring isn't exactly right for my log types (custom logs) but any coloring makes it easier for me to follow a log.
    – rennat
    Oct 21, 2011 at 19:49
  • For me 'grc' on Debian errors out with: OSError: [Errno 13] Permission denied. Also it depends on Python being installed so it's not relaly lightweight unless you already have it. I have found 'ccze' to work much better, ex. 'tail -f -n 50 /var/log/starbound-server.log | ccze -A'. Dec 9, 2013 at 3:56
  • 1
    grc default settings in Ubuntu didn't display nice for syslogs or mail.log. It is not easy to understand how to customize it.
    – lepe
    Jan 27, 2014 at 3:34
  • 2
    I found it quicker and easier way to colorize than multitail. Just did a quick install via source on my CentOS system and upgraded my life. Will install on my other systems too.
    – zeeshan
    Jul 12, 2014 at 9:51
  • 5
    This looks pretty terrible on nginx logs i.imgur.com/aJbIOfL.png
    – mpen
    Sep 3, 2014 at 2:34
54

Have you had a look at ccze? You have the possibility to customize the default colors of some keywords using the option -c or directly in your configuration file. If your screen is clearing after colorizing you must use option -A.

Edit:

If you really would like to have the complete line colored in red, you could also have a try at the following:

$ tail -f myfile.log | perl -pe 's/.*SEVERE.*/\e[1;31m$&\e[0m/g'

\e[1;31m will give you the red color. If you would like some yellow, use \e[1;33m, and for green use \e[1;32m. The \e[0m restores the normal text color.

11
  • 1
    This doesn't work on Mac - I'm upvoting it because it works on Linux. Mar 1, 2011 at 21:33
  • Upvoting because while the perl/ansi trick might not, ccze does.
    – Shadur
    Nov 13, 2011 at 16:02
  • 1
    You can also make your terminal send an alert or "beep" by adding \007 to the end of the regex, like so: perl -pe 's/(ERROR)/\033[31m$1\033[0m\007/g;'. This works awesome if you are using tmux with set -g bell-action any, in which case if you have your log tailing in another window, that window name will alert whenever the regex finds a match. Nov 13, 2012 at 4:15
  • @AmirAfghani This is a linux/unix SE site, therefore I am not sure why you thought it would work on mac. Jun 4, 2013 at 6:06
  • 2
    @BЈовић Mac is a Unix.
    – Chris Down
    Sep 12, 2013 at 19:16
46

Have a look at lnav, the advanced log file viewer.

lnav lnav

It can also pretty print various formats.

Before:

lnav-before-pretty

After:

lnav-pretty

4
  • Really cool addition to the log analysis tool kit. Thanks for the suggestion. Aug 22, 2019 at 10:51
  • Thanks @bagonyi, it's a great tool indeed. It provide a query tool using SQL statements like select log_time, log_level, log_body from syslog_log where log_body like '%CPU%'
    – campisano
    Aug 29, 2020 at 17:49
  • Available in Fedora
    – Yetti99
    Jan 30, 2021 at 19:05
  • Amazing tool. The shortcuts to go to previous/next error and also to move 1h back and forth is incredibly useful.
    – qwertzguy
    Jun 9, 2021 at 5:50
30

You can use rainbow, which colorizes lines based on regular expressions:

rainbow --red='SEVERE.*' --green='INFO.*' tail -f my-file.log

It also comes bundled with predefined configs, for example for Tomcat logs:

rainbow --config=tomcat tail -f my-file.log

(disclaimer: I am the author)

3
  • 5
    I tried most of the other solutions offered to this question, but rainbow was the only one that worked equally well on sun, aix, linux, termux, darwin, and cygwin -- the 6(!) environments I use on a daily basis. All the others involved difficult non-portable build processes for at least some platforms.
    – Stabledog
    May 17, 2017 at 15:15
  • 3
    rainbow is awesome. Are you the author? If so, please edit your answer with that attribution.
    – bishop
    Sep 19, 2019 at 16:56
  • yes, sorry, edited
    – nicoulaj
    Sep 20, 2019 at 17:22
19

You can use colortail:

colortail -f /var/log/messages
6
  • 2
    +1 available at Ubuntu repositories. What I like of colortail compared to ccze is that you can customize freely your patterns using RegEx. Available colors: black, brightblack, white, brightwhite, magenta, brightmagenta, cyan, brightcyan, green,‌​brightgreen, yellow, brightyellow, red,brightred, blue, brightblue. Unfortunately there is no way to set bold or other colors like orange.
    – lepe
    Jan 27, 2014 at 3:55
  • I would like to correct one point about my previous comment: "bright"+color includes "bold" (some colors will actually look brighter as well)
    – lepe
    Jan 27, 2014 at 4:25
  • I tried this on Ubuntu 18 and it did not work. The setup is multi-step and instructions are ambiguous. Still unsure that's the part I got wrong; the last part can get clearer "After that you may want to copy and edit the example config files to some other place. I have them in ~/.colortail/"
    – Dawoodjee
    May 5, 2019 at 11:19
  • Just install colortail with, apt install colortail and it should work without editing ~/.colortail/ too.
    – Kartik M
    May 6, 2019 at 12:05
  • Works like a charm on Ubuntu LTS 20.04 arm64 for Raspberry Pi 4 - apt install colortail gets the job done.
    – alphaGeek
    May 7, 2021 at 11:21
13

Also note that if you just want to look for one matching regex, GNU grep with --color will work — just pipe your tail output through that.

3
  • The OP only wanted to highlight the output, not filter it. Grep won't show non-matching lines...
    – Coderer
    Jun 30, 2014 at 12:36
  • 6
    If you say grep  -A9999  -B9999 regex, it will show all lines unless you have 10,000 non-matching lines in a row.  Use something like GREP_COLORS="ms=31:sl=33:cx=32" grep -A9999 -B9999 SEVERE to show the word SEVERE in red, the rest of SEVERE lines in yellow, and all other (non-SEVERE) lines (up to 9999) in green. Aug 7, 2015 at 2:45
  • You might need to pass --color=always to grep instead of just --color, depending on the order of your pipe, but yes, this works tail (GNU coreutils) 8.27 installed on my box. Jul 2, 2018 at 15:26
11

To get colored output from standard commands like grep, you should set this alias in your .bashrc

# User specific aliases and functions
alias grep='grep --color=auto'

when you grep something in your file you see something like this, (but probably in red):

[root@linuxbox mydir]# grep "\(INFO\|SEVERE\)" /var/log/logname
this entry is an INFO 
SEVERE this entry is a warn!
this entry is an INFO
this entry is an INFO
SEVERE this entry is a warn!

if want to use tail or awk and want that the color survive to a pipe, then the alias is not enough and you should use the --color=always parameter, for example:

[root@linubox mydir]# grep --color=always "\(INFO\|SEVERE\)" /var/log/logname | tail -f | awk '{ print $1 }'
this 
SEVERE
this
this
SEVERE

If you want color text with awk the story is a little bit complex but more powerfull, for example:

[root@linubox mydir]# tail -f /var/log/messages | awk '{if ($5 ~ /INFO/) print "\033[1;32m"$0"\033[0m"; else if ($1 ~ /SEVERE/) print "\033[1;31m"$0"\033[0m"; else print $0}'
this entry is an INFO 
SEVERE this entry is a warn!
this is another ENTRY
this entry is an INFO
this is another ENTRY
this entry is an INFO
SEVERE this entry is a warn!

with each line in its own color.

There are many other way to get colorized text from shell with other tools and they are well descripted by other members.

2
  • Thank you for this. I already knew grep --color to be the simplest and best option for me, but I was having trouble with it and pipe. I didn't know specifying color=always would do it! That is awesome, and I appreciate it very much. This is the best solution of any for me on this page.
    – ctrlbrk
    Apr 12, 2020 at 18:43
  • This is the correct answer. The accepted answer is wrong, as per SO tradition. Feb 9 at 17:53
7

I quite like colorex. Simple, yet satisfying.

tail -f /var/log/syslog | colorex -G '[0-9]{2}:[0-9]{2}:[0-9]{2}' -b $(hostname)
1
  • 14
    how is that simple? Apr 13, 2015 at 10:40
6

Based on @uloBasEI answer, I've tried to use ... | perl ... | perl ..., but Linux pipe gets a bit crazy and is too slow. If I put all rules in only one perl command, it works fine.

For example, create a perl file colorTail.pl as below:

#!/usr/bin/perl -w

while(<STDIN>) {
    my $line = $_;
    chomp($line);
    for($line){
        s/==>.*<==/\e[1;44m$&\e[0m/gi; #tail multiples files name in blue background
        s/.*exception.*|at .*/\e[0;31m$&\e[0m/gi;  #java errors & stacktraces in red
        s/info.*/\e[1;32m$&\e[0m/gi; #info replacement in green
        s/warning.*/\e[1;33m$&\e[0m/gi; #warning replacement in yellow
    }
    print $line, "\n";
}

Use it as:

tail -f *.log | perl colorTail.pl
tail -f *.log -f **/*.log | perl colorTail.pl

NOTE: you can use it on MobaXTerm too! Just download perl plug-in from MobaXTerm site.

4
tail -f /var/log/logname | source-highlight -f esc -s log
6
  • 7
    source-highlight isn't a widely installed command, so you should at least give a link to the project site. Mar 16, 2011 at 22:45
  • Available in Fedora 19.
    – sjas
    Sep 29, 2013 at 14:55
  • And Ubuntu 12.10.
    – sjas
    Sep 29, 2013 at 15:10
  • It looks nice. Its a big package compared to others in this list (26MB). It supports a huge list of languages. It can be customized modifying the config files located at: /usr/share/source-highlight/*.lang (Ubuntu). If you need something simple, go with ccze or colortail.
    – lepe
    Jan 27, 2014 at 3:46
  • looks like it depends on boost, which is around 462MB
    – ecsos
    May 29, 2014 at 21:34
3

One solution that works for coloring all sorts of text, not just logfiles, is a Python tool, 'colout'.

pip install colout
myprocess | colout REGEX_WITH_GROUPS color1,color2... [attr1,attr2...]

Where any text in the output of 'myprocess' which matches group 1 of the regex will be colored with color1, group 2 with color2, etc.

For example:

tail -f /var/log/mylogfile | colout '^(\w+ \d+ [\d:]+)|(\w+\.py:\d+ .+\(\)): (.+)$' white,black,cyan bold,bold,normal

i.e. the first regex group (parens) matches the initial date in the logfile, the second group matches a python filename, line number and function name, and the third group matches the log message that comes after that. This looks like:

logfile with colored formatting

Note that lines or parts of lines which don't match any of my regex are still echoed, so this isn't like 'grep --color' - nothing is filtered out of the output.

Obviously this is flexible enough that you can use it with any process, not just tailing logfiles. I usually just whip up a new regex on the fly any time I want to colorize something. For this reason, I prefer colout to any custom logfile-coloring tool, because I only need to learn one tool, regardless of what I'm coloring: logging, test output, syntax highlighting snippets of code in the terminal, etc.

2
  • 1
    I haven’t seen a single answer that modified the source log file
    – Dani_l
    Dec 7, 2017 at 15:38
  • @Dani_l Right you are! At the time I wrote this, I must have confused myself by flipping back and forth between this and a similar question, to which many of the answers were about how to configure logging such that the ANSI characters were written directly into the log file itself. I'll delete that complaint from my answer. Dec 7, 2017 at 17:10
2

Shameless plug: I wrote a tool called TxtStyle that does something similar as the options mentioned earlier. You can run it as follows:

tail -f /var/log/syslog | txts --regex '\d+'

You can also define named styles in the config file (~/.txts.conf) and use it like so:

ifconfig | txts --name ifconfig

(ifconfig style is defined out of the box)

2

grc for sure!

customize your collors with regex in the file: ~.grc/conf.tail (or whatever name you want)

regexp=.*(select .*)$
colours=unchanged,cyan
=====
regexp=.*(update .*)$
colours=unchanged,bold yellow
=====
regexp=.*(insert .*)$
colours=unchanged,bold yellow
=====
regexp=.*(emp=\d+).*
colours=unchanged,reverse green
=====
regexp=.*http.*/rest/contahub.cmds.(.*?)/(\w*).*$
colours=unchanged,green,magenta
=====
regexp=.*http.*/M/.*\.(.*?Facade)/(\w*).*$
colours=unchanged,underline green,underline magenta

command line:

grc -c conf.tail tail -f log/tomcat/catalina.out

results: screenshot

info for configuring grc: https://github.com/manjuraj/config/blob/master/.grc/sample.conf

2

As for the color codes, I would use tput:

red=$( tput -Txterm setaf 1 )
norm=$( tput -Txterm sgr0 )
bold=$( tput -Txterm bold )

See for reference: man tput

Then:

tail -F myfile.log | sed "s/\(.ERROR.*\)/$red$bold\1$norm/g"
1
  • 1
    Great, thanks. Works like a charm with standard shell functions. Jul 13, 2018 at 8:56
1

I wrote a bash function that accepts up to three parameters and does a grep-like filter on a text file, and outputs text to the screen in color.

I would also like to see a tail function that would do this, but haven't found one yet.

This function can also be improved - I'd appreciate any help on how to make it better.

function multigrep(){

    #THIS WORKS - Recreate this, using input parameters
    #sed -En '/(App)|(Spe)/p' ./flashlog.txt;

    filename="/Users/stevewarren/Library/Preferences/Macromedia/Flash\ Player/Logs/flashlog.txt";
    paramString="";

    for element in "$@"
        do
            #echo $element;
            paramString="$paramString($element)|";
        done

    #TRIM FINAL | OFF PARAMSTRING
    paramString=${paramString:0:${#paramString}-1};

    #CREATE SED EXPRESSION - '/($1)|($2)|(...)/p'
    paramString="'/$paramString/p'";

    #CREATE SED FUNCTION, CALL ON FILE
    paramString="sed -En $paramString ./flashlog.txt"

    echo $paramString;
    echo "${txtbld}$(tput setaf 7)" > ./flashlog_output.txt;
    eval $paramString >> ./flashlog_output.txt;
    echo >> ./flashlog_output.txt;
    #cat ./flashlog_output.txt;

    cat ./flashlog_output.txt | while read LINE
    do

        [[  $1 && ${1-x} ]] && 
            if grep -q $1 <<<$LINE; then
                echo "$(tput setaf 3)$LINE"
            fi

        [[  $2 && ${2-x} ]] && 
            if grep -q $2 <<<$LINE; then
                echo "$(tput setaf 7)$LINE"
            fi


        [[  $3 && ${3-x} ]] && 
            if grep -q $3 <<<$LINE; then
                echo "$(tput setaf 6)$LINE"
            fi

    done
}
1

sure !

I wrote long a go a function called "egrepi", based on the 8 color variables definitions. This works ONLY piped like a "tail -f" colored function.

1. setColors

first, the color variables function to be called at first:


setColors ()
{
set -a
which printf >/dev/null 2>&1 && print=printf || print=print # Mandriva doesn't know about printf

hide='eval tput civis'
show='eval tput cnorm'
CLS=$(tput clear)
bel=$(tput bel)

case ${UNAME} in
AIX)
# text / foreground
N=$(${print} '\033[1;30m')
n=$(${print} '\033[0;30m')
R=$(${print} '\033[1;31m')
r=$(${print} '\033[0;31m')
G=$(${print} '\033[1;32m')
g=$(${print} '\033[0;32m')
Y=$(${print} '\033[1;33m')
y=$(${print} '\033[0;33m')
B=$(${print} '\033[1;34m')
b=$(${print} '\033[0;34m')
M=$(${print} '\033[1;35m')
m=$(${print} '\033[0;35m')
C=$(${print} '\033[1;36m')
c=$(${print} '\033[0;36m')
W=$(${print} '\033[1;37m')
w=$(${print} '\033[0;37m')
END=$(${print} '\033[0m')

# background
RN=$(${print} '\033[6;40m')
Rn=$(${print} '\033[40m')
RR=$(${print} '\033[6;41m')
Rr=$(${print} '\033[41m')
RG=$(${print} '\033[6;42m')
Rg=$(${print} '\033[42m')
RY=$(${print} '\033[6;43m')
Ry=$(${print} '\033[43m')
RB=$(${print} '\033[6;44m')
Rb=$(${print} '\033[44m')
RM=$(${print} '\033[6;45m')
Rm=$(${print} '\033[45m')
RC=$(${print} '\033[6;46m')
Rc=$(${print} '\033[46m')
RW=$(${print} '\033[6;47m')
Rw=$(${print} '\033[47m')

HIGH=$(tput bold)
SMUL=$(tput smul)
RMUL=$(tput rmul)
BLINK=$(tput blink)
REVERSE=$(tput smso)
REVERSO=$(tput rmso)
;;
*)
# text / foreground
n=$(tput setaf 0)
r=$(tput setaf 1)
g=$(tput setaf 2)
y=$(tput setaf 3)
b=$(tput setaf 4)
m=$(tput setaf 5)
c=$(tput setaf 6)
w=$(tput setaf 7)
N=$(tput setaf 8)
R=$(tput setaf 9)
G=$(tput setaf 10)
Y=$(tput setaf 11)
B=$(tput setaf 12)
M=$(tput setaf 13)
C=$(tput setaf 14)
W=$(tput setaf 15)
END=$(tput sgr0)

HIGH=$(tput bold)
SMUL=$(tput smul)
RMUL=$(tput rmul)
BLINK=$(tput blink)
REVERSE=$(tput smso)
REVERSO=$(tput rmso)

# background
Rn=$(tput setab 0)
Rr=$(tput setab 1)
Rg=$(tput setab 2)
Ry=$(tput setab 3)
Rb=$(tput setab 4)
Rm=$(tput setab 5)
Rc=$(tput setab 6)
Rw=$(tput setab 7)
RN=$(tput setab 8)
RR=$(tput setab 9)
RG=$(tput setab 10)
RY=$(tput setab 11)
RB=$(tput setab 12)
RM=$(tput setab 13)
RC=$(tput setab 14)
RW=$(tput setab 15)
;;
esac

BLUEf=${B}
BLUE=${b}
REDf=${R}
RED=${r}
GREENf=${G}
GREEN=${g}
YELLOWf=${Y}
YELLOW=${y}
MANGENTAf=${M}
MANGENTA=${m}
WHITEf=${W}
WHITE=${w}
CYANf=${C}
CYAN=${c}

OK="${RG}${n}OK${END}"
KO="${RR}${n}KO${END}"
NA="${N}NA${END}"

COLORIZE='eval sed -e "s/{END}/${END}/g" -e "s/{HIGH}/${HIGH}/g" -e "s/{SMUL}/${SMUL}/g" -e "s/{RMUL}/${RMUL}/g" -e "s/{BLINK}/${BLINK}/g" -e "s/{REVERSE}/${REVERSE}/g" -e "s/{REVERSO}/${REVERSO}/g"'
LOWS=' -e "s/{n}/${n}/g" -e "s/{r}/${r}/g" -e "s/{g}/${g}/g" -e "s/{y}/${y}/g" -e "s/{b}/${b}/g" -e "s/{m}/${m}/g" -e "s/{c}/${c}/g" -e "s/{w}/${w}/g"'
HIGHS=' -e "s/{N}/${N}/g" -e "s/{R}/${R}/g" -e "s/{G}/${G}/g" -e "s/{Y}/${Y}/g" -e "s/{B}/${B}/g" -e "s/{M}/${M}/g" -e "s/{C}/${C}/g" -e "s/{W}/${W}/g"'
REVLOWS=' -e "s/{Rn}/${Rn}/g" -e "s/{Rr}/${Rr}/g" -e "s/{Rg}/${Rg}/g" -e "s/{Ry}/${Ry}/g" -e "s/{Rb}/${Rb}/g" -e "s/{Rm}/${Rm}/g" -e "s/{Rc}/${Rc}/g" -e "s/{Rw}/${Rw}/g"'
REVHIGHS=' -e "s/{RN}/${RN}/g" -e "s/{RR}/${RR}/g" -e "s/{RG}/${RG}/g" -e "s/{RY}/${RY}/g" -e "s/{RB}/${RB}/g" -e "s/{RM}/${RM}/g" -e "s/{RC}/${RC}/g" -e "s/{RW}/${RW}/g"'
# COLORIZE Usage:
# command |${COLORIZE} ${LOWS} ${HIGHS} ${REVLOWS} ${REVHIGHS}

set +a
}

2. egrepi

and the egrepi function, effective and elegant: color cycling between 8 or more colors (your needs) AND tested under 3 different unix OS, with comments :


# egrepi() egrep with 8 REVERSE cyclic colorations on regexps almost like egrep
# egrepi 
# current script will work for KSH88, KSH93, bash 2+, zsh, under AIX / Linux / SunOS
egrepi ()
{
args=$*
# colorList=wBcgymrN                                                # KSH93 or bash 3+, not for AIX
# set -A color                                                  # needed with older sh
color[0]=$Rw; color[1]=$RB; color[2]=$Rc; color[3]=$Rg; color[4]=$Ry; color[5]=$Rm; color[6]=$Rr; color[7]=$RN; # this is the only one AIX solution
i=0
unset argsToGrep argsSedColor argsPerlColor

for arg in ${args}
do
    [ "${arg}" == "." ] && arg=\\.                              # if you wanna grep "."
    # color=R${colorList:((${RANDOM: -1:1})):1}                     # bash RANDOMized colors
    # color=R${colorList:$i:1} && let i++ && ((i==8)) && i=0                # KSH93 or bash 3+, not for AIX
    argsToGrep="${argsToGrep}${argsToGrep:+|}${arg}"
    # argsSedColor="${argsSedColor} -e s#${arg}#$n${!color}&${w}#gI"            # AIX KSH88 do not recognise this fucking variable double expansion
    # argsSedColor="${argsSedColor} -e s#${arg}#$n${color[$i]}&${w}#gI"         # AIX neither do include sed with Ignore case
    argsPerlColor="${argsPerlColor}${argsPerlColor:+,}s#${arg}#$n${color[$i]}$&${END}#gi"   # So: gotta use perl
    let i+=1 && ((i==8)) && i=0                             # AIX KSH88 do not recognise "let i++"
done
# egrep -i "${argsToGrep}" | sed ${argsSedColor} | egrep -v "grep|sed"              # AIX sed incompatibility with Ignore case
# (($# > 0)) && (egrep -i "${argsToGrep}" | perl -p -e ${argsPerlColor}) || cat         # this line colors & grep the words, will NOT act as "tail -f"
(($# > 0)) && (perl -p -e ${argsPerlColor}) || cat                      # this line just colors the words
}

3. Usage

command | egrepi word1 .. wordN

1

You might also want to take a look at lwatch:

tail -f /var/log/syslog | lwatch --input -

1

for Centos

yum install -y ccze
tail -f /var/log/file.log | ccze -A
1
  • FYI, ccze package is removed from centos 8 epel repo.
    – Akhil
    Sep 1, 2020 at 15:57
0

Publishes some time ago Node Js utility - log-color-highlight

tail -f file | lch -red error warn -green success
lch -f file -red.bold error warn -underline.bgGreen success
0

Based on the @this post, I've created a solution which shows dynamic tail output from the multiple logs files and returns coloured warning and error messages as below:

tail -f -n 5 application.log debug.log| perl -pe 's#WARNING#\x1b[33m$&#; s#ERROR#\x1b[31m$&#; s#foo#\x1b[32m$&#' 

No installation needed. Hope this helps someone.

0

Working solution on Mac

Colored logs on mac

Tried a bunch of things that just didn't work because of some escaping issue.

Eventually found a working solution:

tail -f example.log | sed \
-e "s/FATAL/"$'\e[31m'"&"$'\e[m'"/" \
-e "s/ERROR/"$'\e[31m'"&"$'\e[m'"/" \
-e "s/WARNING/"$'\e[33m'"&"$'\e[m'"/" \
-e "s/INFO/"$'\e[32m'"&"$'\e[m'"/" \
-e "s/DEBUG/"$'\e[34m'"&"$'\e[m'"/"

A quick way to show it working:

echo " [timestamp] production.FATAL Some Message\n" \
"[timestamp] production.ERROR Some Message\n" \
"[timestamp] production.WARNING Some Message\n" \
"[timestamp] production.INFO Some Message\n" \
"[timestamp] production.DEBUG Some Message\n"  | sed \
-e "s/FATAL/"$'\e[31m'"&"$'\e[m'"/" \
-e "s/ERROR/"$'\e[31m'"&"$'\e[m'"/" \
-e "s/WARNING/"$'\e[33m'"&"$'\e[m'"/" \
-e "s/INFO/"$'\e[32m'"&"$'\e[m'"/" \
-e "s/DEBUG/"$'\e[34m'"&"$'\e[m'"/"

Note: this won't hide any logs, just color the parts needed

2
  • Welcome to the site, and thank you for your contribution. Please note however that the approach of using sed to post-process the raw output and introduce color escape codes was already mentioned in the answer by @Gilles. Please review your answer and decide whether your approach is sufficiently distinct to warrant a post of its own, or if it should rather be an edit to add details to the mentioned answer.
    – AdminBee
    Nov 9, 2021 at 8:16
  • @AdminBee Thanks :) and hello. While the other question mentions using sed, it doesn't work on Mac, I've tried it. The start of the line gets replaced with o033[32m and end o033[39m, and its not coloured. I believe this is because the way unix escapes part of it. Ive searched high and wide for a solution to this, but nothing worked. Nov 9, 2021 at 9:40
0
sudo apt install grc
grc tail /var/log/syslog
alias tail='grc tail'

enter image description here

2
  • This is a duplicate of thias’ answer. Feb 22 at 13:56
  • It really should refer to the existing answer as a basis; I see the addition of alias tail='grc tail' here which seems unique among the existing answers. That does address the question "What kind of alias can I setup for a tail command...`". Perhaps a suggested edit would have been better?
    – Jeff Schaller
    Feb 22 at 19:35

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