Bash函数参数不适用于范围

Question

I'm trying to make a bash function argument work with ranges.

The following working code which gives the desired results:

ddos_attack_mirroring_defense() {
    echo $1;
}

ddos_attack_mirroring_defense() Hi NSA

gives:

Hi NSA

But the following with ranges is not working:

ddos_attack_mirroring_defense() {
    printf "regx32%0.s" {1..$1};
}

ddos_attack_mirroring_defense 5 returns:

regx32

instead of:

regx32regx32regx32regx32regx32

I've tried spaces and other different enclosures such as but they still don't work:

$(1) ${1}

What am I doing wrong here and how can I solve this?

Answer 1

Brace expansion happens before variable expansion. As a result, you can't use variables in ranges, you can only use literals.

See man bash :

The order of expansions is: brace expansion, tilde expansion, parameter, variable and arithmetic expansion and command substitution (done in a left-to-right fashion), word splitting, and pathname expansion.

Answer 2

Try this:

ddos_attack_mirroring_defense() {
     eval printf "regx32%0.s" {1..$1};
}

ddos_attack_mirroring_defense 5

Answer 3

您可以使用Unix实用程序seq产生数字范围。

printf "regx32%0.s" $(seq $1)

Answer 4

You should let the variable expand first before brace expansion. You can use a safe eval to fix that:

ddos_attack_mirroring_defense() {
    eval "printf 'regx32%0.s' {1..$1}"
}

Answer 5

Another way of achieving this:

ddos_attack_mirroring_defense() {
    perl -e "print 'regx32'x$1"
}

Answer 6

A safer alternative to using eval is

ddos_attack_mirroring_defense() {
    printf "regx32"
    for ((i=1; i<=$1; i++)); do
        printf "%0.s" "$i"
    done
}