How to make permutation in bash with N! input?

Question

I have to make a permutation in bash with \"eval\" and \"seq\" commands. So I have to make first a permutation that could contain the same numbers, then I have to filter it

Answer 1

I understand this isn't the seq+eval solution the OP wants but in case anyone in future is looking for an alternative, here's an implementation of the generate() function described in the Wikipedia article on Heap's Algorithm written in awk to solve this problem:

$ cat tst.awk
function generate(n,A,  i) {
    if (n == 1) {
        output(A)
    }
    else {
        for (i=0; i<(n-1); i++) {
            generate(n-1, A)
            swap(A, (n%2?0:i), n-1)
        }
        generate(n-1, A)
    }
}

BEGIN{
    if (n>0) {
        for (i=1; i<=n; i++) {
            A[i-1] = i
        }
        generate(n, A)
    }
}

function output(a, i,g) {g=length(a); for (i=0;i<g;i++) printf "%s%s",a[i],(i<(g-1)?"":ORS)}
function swap(a,x,y, t) {t=a[x]; a[x]=a[y]; a[y]=t }

$ awk -v n=3 -f tst.awk | sort
123
132
213
231
312
321

I stuck to the Wikipedia article naming and other conventions as much as possible, including starting the array at zero instead of the typical awk 1, for ease of comparison between that article and the awk code.

Answer 2

If someones curious, heres the solution:

input=3
for i in $(eval echo " {1..$input}{1..$input}{1..$input} "); do
    OK=yes
    for pos1 in $(seq 0 $((x,1)) ); do
        for pos2 in $(seq 0 $((x,1)) ); do
            if [ $pos1 != $pos2 ]; then
                if [ ${i:$pos1:1} == ${i:$pos2:1} ]; then
                    OK=no
                fi
            fi
        done
    done
    if [ $OK = yes ]; then
        echo $i
    fi

done

Answer 3

It is a permutation problem, so I have found some others have did it. You can see the answer Generating permutations using bash

So through the answer, you can write the code like this:

perm() {
    local items="$1"
    local out="$2"
    local i
    [[ "$items" == "" ]] && echo "$out" && return
    for (( i=0; i<${#items}; i++ )) ; do
        perm "${items:0:i}${items:i+1}" "$out${items:i:1}"
    done
}

test() {
    local number="$1"
    local iniitem="$(seq -s' ' 1 ${number} | sed -n 's/ //g;p')"
    perm "$iniitem"
}

Then you can use the function like this:
test 3:
the output:

123
132
213
231
312
321