# FUNCTIONS -- using functions in shell scripts

# $Id$
# Carlos Duarte <cgd@mail.teleweb.pt>, 981006/990220


USING FUNCTIONS
---------------

If /bin/sh support functions, then each function act as "an internal
program": it is called like an external program, it returns a status
like a command, and it interacts with main program by reading from stdin,
and writing to stdout.

my_func() {
	# variables local to my_func, this is not support by every
	# shells that support functions
	local vars

	# code
	# use $1 .. $9, for local arguments (passed as: my_func arg1 ...)
	# $0 for name of the file

	# return status code
	return 1
}

my_func arg1 arg2 ...		# like a command
if test $? -eq 0; then		# status code returned, like a command
	echo ok
else
	echo bad
fi

my_func aa && echo ok

if my_func aa; then :; else
	echo bad
fi

	
EMULATING FUNCTIONS
-------------------

If functions are not available, the best we can do, is: 

my_func='
	# code. 

	# no args -- direct use of shell variables.
	# return status, is the status of last executed command
'

# call with ...
eval "$my_func"

# or ... 
x=`eval "$my_func"`


EXAMPLES
--------

compute factorial of a number... 

  ... emulating a function

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fact='
	eval n=$1
	res=1
	while test $n -gt 1; do
		res=`expr $res \* $n`
		n=`expr $n - 1`
	done
	echo $res
'

set -- 7
echo -n $1! ... ""
eval "$fact"
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  ... with a real function

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
set -- 6
x=`eval "$fact"`
echo $1! =  $x

fact_f() {
	n=$1
	res=1
	while test $n -gt 1; do
		res=`expr $res \* $n`
		n=`expr $n - 1`
	done
	echo $res
}

echo -n 7! ... ""
fact_f 7
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