Colored output in less when tailing a logfile

colorslesslogssed

I am in dire need of a way to color my less output while reading a file that is constantly being appended.

The file in questions is a Resin servlet container log.

My current "implementation" of the color scheme works using tail -F and sed for editing in colors around keywords. I have four words to color: INFO, WARN, ERROR, DEBUG, one of which occurs once per line.

I have tried using the LESSOPENenvironment variable, but I can't seem to keep reading the log. The file is not tailed once it has been open.

I have very little control over the server, and cannot really install anything other than my own scripts in my home folder, so no packages. The server in question is a RHEL 6.4.

The problem is that less does not keep reading the file.
Is there a way to tail the log continuously using the LESSOPENenvironment variable, or do I need some more complex tools?

Best Answer

The problem lies in the pipes on linux. CTRLc closes the pipe and less cannot reopen the pipe.

The solution I found viable was to redirect the colored log to a file, then read that file with less. A file can be tailed after a CTRL-c, and I therefore just do the following:

tail -F -c +1 | colorize > /tmp/logfilename &
less -Sr /tmp/logfilename

Works like a charm.

Related Solutions

Colors – Can Less Retain Colored Output?

Use:

git diff --color=always | less -r

--color=always is there to tell git to output color codes even if the output is a pipe (not a tty). And -r is there to tell less to interpret those color codes and other escape sequences. Use -R for ANSI color codes only.

How to pipe colored diff output to less

diff cannot output colors, you need another program, such as colordiff for that. Colors in the terminal are printed via ANSI escape codes which less does not interpret by default. To get less to correctly show colors, you need the -r, or even better, -R switch:

colordiff -- "$file1" "$file2" | less -R

From man less:

   -R or --RAW-CONTROL-CHARS
          Like -r, but only ANSI  "color"  escape  sequences  are
          output in "raw" form.  Unlike -r, the screen appearance
          is maintained correctly in most  cases.   ANSI  "color"
          escape sequences are sequences of the form:

               ESC [ ... m

          where  the  "..."  is  zero or more color specification
          characters For the purpose of keeping track  of  screen
          appearance,  ANSI color escape sequences are assumed to
          not move the cursor.  You  can  make  less  think  that
          characters  other  than  "m"  can end ANSI color escape
          sequences by setting the environment  variable  LESSAN‐
          SIENDCHARS  to  the  list of characters which can end a
          color escape sequence.  And you  can  make  less  think
          that characters other than the standard ones may appear
          between the ESC and the m by  setting  the  environment
          variable  LESSANSIMIDCHARS  to  the  list of characters
          which can appear.

Alternatively, you can use more which will display colors correctly by default.

If you cannot install external programs, you should be able to get the same output using a more manual approach:

diff a b | 
   perl -lpe 'if(/^</){$_ = "\e[1;31m$_\e[0m"} 
              elsif(/^>/){$_ = "\e[1;34m$_\e[0m"}'

Best Answer

Related Solutions

Colors – Can Less Retain Colored Output?

How to pipe colored diff output to less

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