Add debug mode to bash script - bash

Question

first of all, sorry for my bad english.
I want to enbale debug mode, with date. I was thinkging in a variable that use one type of redirection, or another, like this:
#!/bin/bash
DEBUG_MODE=1
if [ $CHAMAC_DEBUG = 0 ]; then
output=/dev/null
elif [ $CHAMAC_DEBUG = 1 ]; then
output=>( while read line; do echo "$(date): ${line}"; done >> ~/output.log )
fi
echo "hi, im a echo" &> $output
But it dont work for me.... how can do it¿?¿?

Answer 1

I'm not quite sure what you mean by "debug mode", but if you want to print additional output only when a particular variable is defined you could do something like this:
#!/bin/bash
function print_debug {
[ $DEBUG_MODE -eq 1 ] && echo "$(date) $1"
}
DEBUG_MODE=0
print_debug "Test 1"
DEBUG_MODE=1
print_debug "Test 2"
Output:
$ ./test.sh
Test 2
You could also separate debug output from regular output by echoing debug messages to a different file descriptor:
function print_debug {
[ $DEBUG_MODE -eq 1 ] && echo "$1" 1>&3
}
That way you can redirect STDOUT, STDERR and debug output to different files if needed.

Answer 2

Your question is hard to understand, but perhaps you are looking for something like this?
debug () {
date +"[%C] $*" >&2
}
if ... whatever ...; then
dbg=debug
else
dbg=:
fi
$dbg "script started"
:
Wherever you want to output a diagnostic, use $dbg instead of echo.
(You have to double any literal percent sign in your debug prints, or make the function slightly more complex.)

Answer 3

You can use an alternate file descriptor for this (along with a few other fixes):
if [[ "${CHAMAC_DEBUG}" == "1" ]]
then
exec 3>> ~/output.log
else
exec 3>> /dev/null
fi
{ echo "$(date) : hi, im a echo"; } >&3
The process substitution syntax wants to see the name of a program, not a bash internal command like while. You could maybe get it to work using something like >(bash -c 'some stuff here'), but the above is simpler, I think. The only downside is you have to do your own date-stamping... If that's a problem, you could look into submitting your debug messages to syslog (via logger) and configure that to dump those specific messages in a file of their own...