Question

I have bash script where i have echo before every command showing what is happening.

But i need to disbale echo when setting as cron job and then enable again if do some testing.

i find it very hard to go to each line and then add/remove comment

is there anything which i can include at top something like

enable echo or disable echo

so that i don’t have to waste time

Answer 1

The absolute easiest would be to insert the following line after the hashbang line:

echo() { :; }

When you want to re-enable, either delete the line or comment it out:

#echo() { :; }

If you’re not using echo but printf, same strategy, i.e.:

printf() { :; }

If you absolutely need to actually echo/printf something, prepend the builtin statement, e.g.:

builtin echo "This 'echo' will not be suppressed."

This means that you can do a conditional output, e.g.:

echo () {
  [[ "$SOME_KIND_OF_FLAG" ]] && builtin echo $@
}

Set the SOME_KIND_OF_FLAG variable to something non-null, and the overridden echo function will behave like normal echo.

---

EDIT: another alternative would be to use echo for instrumenting (debugging), and printf for the outputs (e.g., for piping purposes). That way, no need for any FLAG. Just disable/enable the echo() { :; } line according to whether you want to instrument or not, respectively.

---

Enable/Disable via CLI Parameter

Put these lines right after the hashbang line:

if [[ debug == "$1" ]]; then
  INSTRUMENTING=yes  # any non-null will do
  shift
fi
echo () {
  [[ "$INSTRUMENTING" ]] && builtin echo $@
}

Now, invoking the script like this: script.sh debug will turn on instrumenting. And because there’s the shift command, you can still feed parameters. E.g.:

• Without instrumenting: script.sh param1 param2
• With instrumenting: script.sh debug param1 param2

The above can be simplified to:

if [[ debug != "$1" ]]; then
  echo () { :; }
  shift
fi

if you need the instrumenting flag (e.g. to record the output of a command to a temp file only if debugging), use an else-block:

if [[ debug != "$1" ]]; then
  echo () { :; }
  shift
else
    INSTRUMENTING=yes
fi

REMEMBER: in non-debug mode, all echo commands are disabled; you have to either use builtin echo or printf. I recommend the latter.