Empty function in BASH - bash

Question

I'm using FPM tool to create .deb package. This tool create before/after remove package from supported files.
Unfortunatly the bash script generated by FPM contains such function
dummy() {
}
And this script exit with an error:
Syntax error: "}" unexpected
Does BASH doesn't allow empty functions? Which version of bash/linux have this limitation?

Answer 1

You could use : that is equivalent to true and is mostly used
as do nothing operator...
dummy(){
:
}

Answer 2

A one liner
dummy(){ :; }
: is the null command
; is needed in the one line format

Answer 3

An empty bash function may be illegal. function contains only comments will be considered to be empty too.
a ":" (null command) can be placed in function if you want to "DO NOTHING"
see: http://tldp.org/LDP/abs/html/functions.html

Answer 4

I recommend this one:
dummy(){ unused(){ :;} }
If you use : null command, it will be printed by xtrace option:
(
set -o xtrace
dummy(){ :; }
dummy "null command"
)
echo ------
(
set -o xtrace
dummy(){ unused(){ :;} }
dummy "unused function"
)
output:
+ dummy 'null command'
+ :
------
+ dummy 'unused function'
For debug I use wrapper like this:
main() {(
pwd # doing something in subshell
)}
print_and_run() {
clear
(
eval "$1() { unused() { :; } }"
set -o xtrace
"$#"
)
time "$#"
}
print_and_run main aaa "bb bb" ccc "ddd"
# output:
# + main aaa 'bb bb' ccc ddd
# ..

Answer 5

dummy_success(){ true; } #always returns 0
dummy_fail(){ false; } #always returns 1
minimal functions returning always OK or ERROR status..
also useful to redefine missing functions with empty function
(or update it with some default action, for example - debug warning):
#!/bin/sh
#avoid error if calling unimportant_func which is underfined
declare -F unimportant_func >/dev/null || unimportant_func() { true; }
#get error if calling important_func which is underfined
declare -F important_func >/dev/null || important_func() { false; }
# print debug assert if function not exists
declare -F some_func >/dev/null || some_func() {
echo "assert: '${FUNCNAME[0]}() is not defined. called from ${BASH_SOURCE[1]##*/}[${BASH_LINENO[0]}]:${FUNCNAME[1]}($#)" 1>&2; }
my_func(){
echo $(some_func a1 a2 a3)
important_func && echo "important_func ok" || echo "important_func error"
unimportant_func && echo "unimportant_func ok" || echo "unimportant_func error"
}
my_func
output:
$> testlib.sh
assert: 'some_func() is not defined. called from testlib.sh[15]:my_func(a1 a2 a3)
important_func error
unimportant_func ok