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Basic logging commands for Linux shell scripts
#!/bin/bash
##
## Simple logging mechanism for Bash
##
## Author: Michael Wayne Goodman <goodman.m.w@gmail.com>
## Thanks: Jul for the idea to add a datestring. See:
## http://www.goodmami.org/2011/07/simple-logging-in-bash-scripts/#comment-5854
## Thanks: @gffhcks for noting that inf() and debug() should be swapped,
## and that critical() used $2 instead of $1
##
## License: Public domain; do as you wish
##
exec 3>&2 # logging stream (file descriptor 3) defaults to STDERR
verbosity=3 # default to show warnings
silent_lvl=0
crt_lvl=1
err_lvl=2
wrn_lvl=3
inf_lvl=4
dbg_lvl=5
notify() { log $silent_lvl "NOTE: $1"; } # Always prints
critical() { log $crt_lvl "CRITICAL: $1"; }
error() { log $err_lvl "ERROR: $1"; }
warn() { log $wrn_lvl "WARNING: $1"; }
inf() { log $inf_lvl "INFO: $1"; } # "info" is already a command
debug() { log $dbg_lvl "DEBUG: $1"; }
log() {
if [ $verbosity -ge $1 ]; then
datestring=`date +'%Y-%m-%d %H:%M:%S'`
# Expand escaped characters, wrap at 70 chars, indent wrapped lines
echo -e "$datestring $2" | fold -w70 -s | sed '2~1s/^/ /' >&3
fi
}
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@goodmami goodmami commented Sep 13, 2013

To make the above working example, append the following to the bottom of the file:

### EXAMPLE COMMAND LINE ARGUMENTS ###

usage() {
    echo "Usage:"
    echo "  $0 [OPTIONS]"
    echo "Options:"
    echo "  -h      : display this help message"
    echo "  -q      : decrease verbosity level (can be repeated: -qq, -qqq)"
    echo "  -v      : increase verbosity level (can be repeated: -vv, -vvv)"
    echo "  -l FILE : redirect logging to FILE instead of STDERR"
}

while getopts "hqvl:" opt; do
    case "$opt" in
       h) usage; exit 0 ;;
       q) (( verbosity = verbosity - 1 )) ;;
       v) (( verbosity = verbosity + 1 )) ;;
       l) exec 3>>$OPTARG ;;
       *) error "Invalid options: $1"; usage; exit 1 ;;
    esac
done
shift $((OPTIND-1))
args="$@"

notify "This logging system uses the standard verbosity level mechanism to choose which messages to print. Command line arguments customize this value, as well as where logging messages should be directed (from the default of STDERR). Long messages will be split at spaces to wrap at a character limit, and wrapped lines are indented. Wrapping and indenting can be modified in the code."

inf "Inspecting argument list: $args"

if [ ! "$args" ]; then
    warn "No arguments given"
else
    for arg in $args; do
        debug "$arg"
    done
fi
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@gffhcks gffhcks commented Sep 21, 2015

Shouldn't "debug" be at a higher level of verbosity than "info"?

Also, why does $2 get used instead of $1 for critical()?

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@goodmami goodmami commented Jul 22, 2016

@gffhcks, sorry to be so late to respond. I didn't get any notification for your comment.

And thanks for pointing these out. Debug and Info are in the unconventional order because I didn't closely check with what other logging frameworks do. I'm not sure why I used $2 in critical(); that's just a bug. I'll fix both of these.

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@MapleLove2014 MapleLove2014 commented Sep 20, 2021

Hello, what does this statement means: sed '2~1s/^/ /' ?

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@goodmami goodmami commented Sep 20, 2021

@MapleLove2014, that indents the wrapped lines. 2~1 means to perform the following operation on every line starting from the 2nd (every 1 line after line 2), then s/^/ / is a substitution operation that matches the beginning of each line (^) and inserts two spaces. In a terminal you might try man sed to get more info about the command.

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