Bash Shell: Check If A Function Exists Or Not (Find Out If a Function Is Defined Or Not)

foo(){ echo "Hello"; }

type foo &>/dev/null && echo "foo() found." || echo "foo() not found."

type foo &>/dev/null && foo

bar(){ echo "Hello, World."; }

declare -F bar &>/dev/null && echo "bar() found." || echo "bar() not found."

declare -F bar && bar

patch_etc_files(){
	local d="${_JAIL_DIR:-/nginx}"
 
        # remove / from each etc/file and build jail specific paths 
	local _passwd="${d}${_passwddb#/}"
	local _shadow="${d}${_shadowdb#/}"
	local _group="${d}${_groupsdb#/}"
	local _hosts="${d}${_hostsdb#/}"
 
	echo 'root:x:0:0:root:/root:/bin/bash' >${_passwd}
	grep "^{$_nginx_user}" ${_passwddb} >>${_passwd} 
 
	echo 'root:!!:14611:0:99999:7:::' >${_shadow}
	grep "^{$_nginx_user}" ${_shadowdb}  >>${_shadow}
 
	egrep "root|{$_nginx_group}" ${_groupsdb} >${_group}
 
        # Call __patch_etc_hosts_file() only if it is defined.
        # Patch /etc/hosts in $d jail, this is a system specific and should be added 
        # in $BASEDIR/hooks.sh (see /usr/local/nixcraft/docs/nginx.README.txt for more info)
	declare -F __patch_etc_hosts_file &>/dev/null && __patch_etc_hosts_file
}