Why is my bash function returning the wrong value?

Question

fact() 
{
    if [ $1 -eq 1 ]
    then
        return 1
    else
        y=`expr $1 - 1`
        fact $y
        b=$(($1 * $?))
        return $b
    fi
}
echo "enter"
read n
fact $n
echo "$?"

This is a program for finding factorial numbers. The output is correct to 5. Pin 6 gives a value of 208, but the correct answer is 720. What causes this error?

Answer 1

Function return values ​​can reach 255:

a()
{
        return 255
}

a
echo $?

b()
{
        return 256
}

b
echo $?

It produces:

$ bash x.sh
255
0

returnsimilar to exit, and exitcan take values ​​up to 255 ( http://www.unix.org/whitepapers/shdiffs.html ).

One option is to switch to an iterative sentence, as described in another answer. Alternatively, you can use the echo and write the recursive output in this way:

#!/bin/bash

fact() 
{
    if [ $1 -eq 1 ]
    then
        echo 1
    else
        y=$(expr $1 - 1)
        f=$(fact $y)
        b=$(($1 * $f))
        echo $b
    fi
}
echo "enter"
read n
fact $n

Answer 2

bourne shell can not $? ( ). 255.

n=0
on=0
fact=1 

echo -n "Enter number to find factorial : "
read n

on=$n

while [ $n -ge  1 ]
do
  fact=`expr $fact \* $n`
  n=`expr $n - 1`
done

echo "Factorial for $on is $fact"

Answer 3

, , - 256. 720 mod 256 is 208 (256 + 256 + 208 = 720).

, , :

#!/bin/bash
fact()
{
    if [ "$1" -eq "1" ]
    then
        echo 1
        return
    fi
    y=`expr $1 - 1`
    z=$(fact $y)
    echo $(($1 * $z))
}
echo "enter"
read n
echo "$(fact $n)"

, .

, , :

pax> echo 'define f(x) {if (x>1){return x*f(x-1)};return 1}
           f(6)' | bc
720
pax> echo 'define f(x) {if (x>1){return x*f(x-1)};return 1}
           f(500)' | BC_LINE_LENGTH=99999 bc
12201368259911100687012387854230469262535743428031928421924135883858
45373153881997605496447502203281863013616477148203584163378722078177
20048078520515932928547790757193933060377296085908627042917454788242
49127263443056701732707694610628023104526442188787894657547771498634
94367781037644274033827365397471386477878495438489595537537990423241
06127132698432774571554630997720278101456108118837370953101635632443
29870295638966289116589747695720879269288712817800702651745077684107
19624390394322536422605234945850129918571501248706961568141625359056
69342381300885624924689156412677565448188650659384795177536089400574
52389403357984763639449053130623237490664450488246650759467358620746
37925184200459369692981022263971952597190945217823331756934581508552
33282076282002340262690789834245171200620771464097945611612762914595
12372299133401695523638509428855920187274337951730145863575708283557
80158735432768888680120399882384702151467605445407663535984174430480
12893831389688163948746965881750450692636533817505547812864000000000
00000000000000000000000000000000000000000000000000000000000000000000
00000000000000000000000000000000000000000000000

bash - 500: -)

Answer 4

, , , bash. , , .

#!/bin/dash

, !

Answer 5

Bash Bash , , , , . grater, 127 ( , , , 127 - 255 - ).

fact $y
b=$(($1 * $?))

$? fact, , 255.

Bash - , .