Bash tips & tricks [ep. 4]: Use logging levels

This is the fourth epidose of a small series.

Description:

Support different logging levels natively in your scripts so that your code will be more stable and maintainable.

BAD:

#!/bin/bash -l
...
# for debug only, comment out when OK
echo $a 
do_something $a

# echo $? # sometimes does not work?

 GOOD:

Nothing to invent, there are already a few blog posts around about the best practices for log messages. I personally like the one from Michael Wayne Goodman:

http://www.goodmami.org/2011/07/04/Simple-logging-in-BASH-scripts.html

I have reused his code in my scripts with very few modifications to fit my needs:

### verbosity levels
silent_lvl=0
crt_lvl=1
err_lvl=2
wrn_lvl=3
ntf_lvl=4
inf_lvl=5
dbg_lvl=6

## esilent prints output even in silent mode
function esilent () { verb_lvl=$silent_lvl elog "$@" ;}
function enotify () { verb_lvl=$ntf_lvl elog "$@" ;}
function eok ()    { verb_lvl=$ntf_lvl elog "SUCCESS - $@" ;}
function ewarn ()  { verb_lvl=$wrn_lvl elog "${colylw}WARNING${colrst} - $@" ;}
function einfo ()  { verb_lvl=$inf_lvl elog "${colwht}INFO${colrst} ---- $@" ;}
function edebug () { verb_lvl=$dbg_lvl elog "${colgrn}DEBUG${colrst} --- $@" ;}
function eerror () { verb_lvl=$err_lvl elog "${colred}ERROR${colrst} --- $@" ;}
function ecrit ()  { verb_lvl=$crt_lvl elog "${colpur}FATAL${colrst} --- $@" ;}
function edumpvar () { for var in $@ ; do edebug "$var=${!var}" ; done }
function elog() {
        if [ $verbosity -ge $verb_lvl ]; then
                datestring=`date +"%Y-%m-%d %H:%M:%S"`
                echo -e "$datestring - $@"
        fi
}

The edumpvar is handy to have the status of several variables at once:

#!/bin/bash -l
# code
#...

verbosity=6

edumpvar ORACLE_SID ORACLE_HOME

<output>
2016-03-15 23:06:10 - DEBUG --- ORACLE_SID=orcl12c
2016-03-15 23:06:10 - DEBUG --- ORACLE_HOME=/u01/app/oracle/product/12.1.0.2
</output>

If you couple the verbosity level with input parameters you can have something quite clever (e.g. -s for silent, -V for verbose, -G for debug). I’m putting everything into one single snippet just as example, but as you can imagine, you should seriously put all the fixed variables and functions inside an external file that you will systematically include in your scripts:

#!/bin/bash -l

colblk='\033[0;30m' # Black - Regular
colred='\033[0;31m' # Red
colgrn='\033[0;32m' # Green
colylw='\033[0;33m' # Yellow
colpur='\033[0;35m' # Purple
colrst='\033[0m'    # Text Reset

verbosity=4

### verbosity levels
silent_lvl=0
crt_lvl=1
err_lvl=2
wrn_lvl=3
ntf_lvl=4
inf_lvl=5
dbg_lvl=6

## esilent prints output even in silent mode
function esilent () { verb_lvl=$silent_lvl elog "$@" ;}
function enotify () { verb_lvl=$ntf_lvl elog "$@" ;}
function eok ()    { verb_lvl=$ntf_lvl elog "SUCCESS - $@" ;}
function ewarn ()  { verb_lvl=$wrn_lvl elog "${colylw}WARNING${colrst} - $@" ;}
function einfo ()  { verb_lvl=$inf_lvl elog "${colwht}INFO${colrst} ---- $@" ;}
function edebug () { verb_lvl=$dbg_lvl elog "${colgrn}DEBUG${colrst} --- $@" ;}
function eerror () { verb_lvl=$err_lvl elog "${colred}ERROR${colrst} --- $@" ;}
function ecrit ()  { verb_lvl=$crt_lvl elog "${colpur}FATAL${colrst} --- $@" ;}
function edumpvar () { for var in $@ ; do edebug "$var=${!var}" ; done }
function elog() {
        if [ $verbosity -ge $verb_lvl ]; then
                datestring=`date +"%Y-%m-%d %H:%M:%S"`
                echo -e "$datestring - $@"
        fi
}

OPTIND=1
while getopts ":sVG" opt ; do
        case $opt in
        s)
                verbosity=$silent_lvl
                edebug "-s specified: Silent mode"
                ;;
        V)
                verbosity=$inf_lvl
                edebug "-V specified: Verbose mode"
                ;;
        G)
                verbosity=$dbg_lvl
                edebug "-G specified: Debug mode"
                ;;
        esac
done

ewarn "this is a warning"
eerror "this is an error"
einfo "this is an information"
edebug "debugging"
ecrit "CRITICAL MESSAGE!"
edumpvar ORACLE_SID

Example:

$ example.sh -s

$ example.sh

$ example.sh -V

$ example.sh -G

It does not take into account the output file. That will be part of the next tip