which()
{
	# on some systems 'which' command is considered deprecated and not installed by default
	# 'command -v' replacement does not work exactly the same way. it outputs shell aliases if present
	# $1 - executable name
	local IFS=:
	for p in $PATH; do
	    [ -x "$p/$1" ] && {
		echo "$p/$1"
		return 0
	    }
	done
	return 1
}
exists()
{
	which "$1" >/dev/null 2>/dev/null
}
existf()
{
	type "$1" >/dev/null 2>/dev/null
}
whichq()
{
	which $1 2>/dev/null
}
exist_all()
{
	while [ -n "$1" ]; do
		exists "$1" || return 1
		shift
	done
	return 0
}
on_off_function()
{
	# $1 : function name on
	# $2 : function name off
	# $3 : 0 - off, 1 - on
	local F="$1"
	[ "$3" = "1" ] || F="$2"
	shift
	shift
	shift
	"$F" "$@"
}
contains()
{
	# check if substring $2 contains in $1
	[ "${1#*$2}" != "$1" ]
}
find_str_in_list()
{
	[ -n "$1" ] && {
		for v in $2; do
			[ "$v" = "$1" ] && return 0
		done
	}
	return 1
}
end_with_newline()
{
	local c=$(tail -c 1)
	[ "$c" = "" ]
}

append_separator_list()
{
	# $1 - var name to receive result
	# $2 - separator
	# $3 - quoter
	# $4,$5,... - elements
	local _var="$1" sep="$2" quo="$3" i

	eval i="\$$_var"
	shift; shift; shift
	while [ -n "$1" ]; do
		if [ -n "$i" ] ; then
			i="$i$sep$quo$1$quo"
		else
			i="$quo$1$quo"
		fi
		shift
	done
	eval $_var="\$i"
}
make_separator_list()
{
	eval $1=''
	append_separator_list "$@"
}
make_comma_list()
{
	# $1 - var name to receive result
	# $2,$3,... - elements
	local var="$1"
	shift
	make_separator_list $var , '' "$@"
}
make_quoted_comma_list()
{
	# $1 - var name to receive result
	# $2,$3,... - elements
	local var="$1"
	shift
	make_separator_list $var , '"' "$@"
}
unique()
{
	local i
	for i in "$@"; do echo $i; done | sort -u | xargs
}

is_linked_to_busybox()
{
	local IFS F P
	
	IFS=:
	for path in $PATH; do
		F=$path/$1
		P="$(readlink $F)"
		if [ -z "$P" ] && [ -x $F ] && [ ! -L $F ]; then return 1; fi
		[ "${P%busybox*}" != "$P" ] && return
	done
}
get_dir_inode()
{
	local dir="$1"
	[ -L "$dir" ] && dir=$(readlink "$dir")
	ls -id "$dir" | awk '{print $1}'
}

linux_min_version()
{
	# $1 - major ver
	# $2 - minor ver
	local V1=$(sed -nre 's/^Linux version ([0-9]+)\.[0-9]+.*$/\1/p' /proc/version)
	local V2=$(sed -nre 's/^Linux version [0-9]+\.([0-9]+).*$/\1/p' /proc/version)
	[ -n "$V1" -a -n "$V2" ] && [ "$V1" -gt "$1" -o "$V1" -eq "$1" -a "$V2" -ge "$2" ]
}
linux_get_subsys()
{
	local INIT=$(sed 's/\x0/\n/g' /proc/1/cmdline | head -n 1)

	[ -L "$INIT" ] && INIT=$(readlink "$INIT")
	INIT=$(basename "$INIT")
	if [ -f "/etc/openwrt_release" ] && [ "$INIT" = "procd" ] ; then
		SUBSYS=openwrt
	else
		# generic linux
		SUBSYS=
	fi
}
openwrt_fw3()
{
	[ ! -x /sbin/fw4 -a -x /sbin/fw3 ]
}
openwrt_fw4()
{
	[ -x /sbin/fw4 ]
}
openwrt_fw3_integration()
{
	[ "$FWTYPE" = iptables ] && openwrt_fw3
}

create_dev_stdin()
{
	[ -e /dev/stdin ] || ln -s /proc/self/fd/0 /dev/stdin
}

call_for_multiple_items()
{
	# $1 - function to get an item
	# $2 - variable name to put result into
	# $3 - space separated parameters to function $1

	local i item items
	for i in $3; do
		$1 item $i
		[ -n "$item" ] && {
			if [ -n "$items" ]; then
				items="$items $item"
			else
				items="$item"
			fi
		}
	done
	eval $2=\"$items\"
}

fix_sbin_path()
{
	local IFS=':'
	printf "%s\n" $PATH | grep -Fxq '/usr/sbin' || PATH="/usr/sbin:$PATH"
	printf "%s\n" $PATH | grep -Fxq '/sbin' || PATH="/sbin:$PATH"
	export PATH
}

fsleep_setup()
{
    [ -n "$FSLEEP" ] || {
	if sleep 0.001 2>/dev/null; then
		FSLEEP=1
	elif busybox usleep 1 2>/dev/null; then
		FSLEEP=2
	else
		local errtext=$(read -t 0.001 2>&1)
		if [ -z "$errtext" ]; then
			FSLEEP=3
		# newer openwrt has ucode with system function that supports timeout in ms
		elif ucode -e "system(['sleep','1'], 1)" 2>/dev/null; then
			FSLEEP=4
		# older openwrt may have lua and nixio lua module
		elif lua -e 'local nixio  = require "nixio"; nixio.nanosleep(0,1);' 2>/dev/null ; then
			FSLEEP=5
		else
			FSLEEP=0
		fi
	fi
    }
}
minsleep()
{
    case "$FSLEEP" in
	1)
		sleep 0.1
		;;
	2)
		busybox usleep 100000
		;;
	3)
		read -t 0.1
		;;
	4)
		ucode -e "system(['sleep','1'], 100)"
		;;
	5)
		lua -e 'local nixio  = require "nixio"; nixio.nanosleep(0,100000000);'
		;;
    	*)
		sleep 1
    esac
}