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Currently I am using tail -f for viewing logs.

Is there any more efficient/readable/better way of viewing logs?

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closed as not constructive by Ƭᴇcʜιᴇ007, BinaryMisfit, Dave, Diogo, 8088 Jan 11 '13 at 17:54

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up vote 1 down vote accepted

Yes! perl stand for Practical Extraction and Research Language.

Instead of using shell syntaxes, like:

tail -f file | grep --line-buffered someting


tail -f file | sed -une '/someting/{s/^.*:/doing some formatting/;p}'

(Nota: --line-buffered in grep, like -u in sed are usefull to prevent buffering by fixed size blocks)

For viewing/browsing logs, perl is the language.

Depending on what you're awaiting for... you may have to build a little script for matching exactly your need.

You may found some useable samples in perlfaq, like in perldoc perlfaq5 (or man perlfaq5 if you've not installed perldoc), there is a question: How do I do a "tail -f" in perl? where I've taked this:

First try

seek(GWFILE, 0, 1);

The statement seek(GWFILE, 0, 1) doesn't change the current position, but it does clear the end-of-file condition on the handle, so that the next <GWFILE> makes Perl try again to read something.

If that doesn't work (it relies on features of your stdio implementation), then you need something more like this:

for (;;) {
    for ($curpos = tell(GWFILE); <GWFILE>; $curpos = tell(GWFILE)) {
      # search for some stuff and put it into files
    # sleep for a while
    seek(GWFILE, $curpos, 0);  # seek to where we had been

I've already used this many times for triggering special cases.


For sample, there is a quick and dirty real-time log counter try it! (need read access to /var/log/syslog ;-) :

#!/usr/bin/perl -w
my %counter;

open FH, "</var/log/syslog" or die;
my $curpos = ( stat FH )[7];
seek( FH, $curpos, 0 );

for ( ; ; ) {
    for ( $curpos = tell(FH) ; <FH> ; $curpos = tell(FH) ) {
        $counter{$3}++ if /^(\S+\s+){4}(\S+\/|)([^\/\[:]*)[\[:]/;
    syswrite STDOUT, sprintf "\r%s\e[K",
      join( ", ", map { sprintf "%s:%s", $_, $counter{$_} } keys %counter );
    select undef,undef,undef,1;
    seek( FH, $curpos, 0 );

Would produce one line, self-refreashing every seconds, containing all seen daemon's name and a counter for each of them:

smtp:6, pop3d-ssl:13, local:6, imapd:8, smtpd:30, CRON:5, pickup:1, named:1
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As F. Hauri suggests, you could use perl to format the output.

For my usage, I created an alias for tail in my ~/.bashrc to read my Glassfish's logs. It is very simple (one line) and colorizes my output to underline error/warning lines:

tail-color() {
    tail $* | perl -p -e 's/(.*WARN.*)/\033[31;43;1m$1\033[0m\007/g;' -e 's/(.*ERROR.*)/\033[33;41;1m$1\033[0m\007/g;' -e 's/(.*SEVERE.*)/\033[33;41;1m$1\033[0m\007/g'
  1. -p : wraps the script inside a loop and outputs the processed line
  2. -e 's/(.*WARN.*)/\033[31;43;1m$1\033[0m\007/g;' colorizes every line containing "WARN"
    • \033[ begins escape sequence (enables formatting)
    • 31 means red foreground
    • 43 means yellow background
    • 1 enables bold characters
    • m closes escape sequence
    • $1 includes the input line
    • \033[0m is a second sequence to put default formatting back to standard, after the line has been outputs
    • \007 beeps
  3. -e 's/(.*ERROR.*)/\033[33;41;1m$1\033[0m\007/g;' colorizes every line containing "ERROR" ; the only differences concern colors:
    • 31 means yellow foreground
    • 43 means red background

In my case, I toggled visual bell on, so my screen blinks on error (and my speaker doesn't beep) and error/warning lines can be detected very quickly.

You can get more information about:

Again, as F. Hauri explains in his answer, you can do many things thanks to perl, so you could "develop" your own log reader depending on your needs.

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For more portability, try to use tput instead of ansi codes: my $red=`tput setf 4` or $bold=`tput bold` or via Term::Cap(3perl). (see man terminfo) – F. Hauri Jan 12 '13 at 20:07
Thanks for the tip! – ssssteffff Jan 13 '13 at 20:55

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