#!/bin/bash
#shellcheck disable=2154,SC2020
mkfile(){
    :>/tmp/test"$1"
    for (( i=0;i<="$1";i++ )); do
        unset str
        for (( j=0;j<=10;j++ )); do
            str=$str${var:$((RANDOM%20)):1}
        done
        echo "$str">>/tmp/test"$1"
    done
}
testfile(){
    hyperfine -w 3 -r 1000 -i \
    "tr -d '\\.' </tmp/test$1 | cut -b1-3" \
    "sed -r 's/\\.//g;s/(...).*/\\1/' /tmp/test$1" \
    "while IFS= read -r line; do unset res; while read -r -n 1 c ; do [[ $c =~ [0-9] ]] && res+=$c; done <<<$line; echo ${res:0:3}; done </tmp/test$1"
}
testcmd(){
    tr -d '\.' </tmp/test10 | cut -b1-3
    sed -r 's/\.//g;s/(...).*/\1/' /tmp/test10
    while IFS= read -r line; do unset res; while read -r -n 1 c ; do [[ $c =~ [0-9] ]] && res+=$c; done <<<"$line"; echo "${res:0:3}"; done </tmp/test10
}

var='0.1.2.3.4.5.6.7.8.9.'
mkfile 10
testcmd
mkfile 1000
testfile 1000
exit

#!/bin/bash
mkfile(){
    :>/tmp/test"$1"
    for (( i=0;i<="$1";i++ )); do
        unset str
        for (( j=0;j<=10;j++ )); do
            str=$str${var:$((RANDOM%20)):1}
        done
        echo "$str">>/tmp/test"$1"
    done
}

test_tr(){
    tr -d '\.' </tmp/test"$count" | cut -b1-3 >/dev/null
}

test_sed(){
    sed -r 's/\.//g;s/(...).*/\1/' /tmp/test"$count" >/dev/null
}

test_while(){
    while IFS= read -r line; do
        unset res
        while read -r -n 1 c ; do
            [[ $c =~ [0-9] ]] && res+=$c
        done <<<"$line"
        echo "${res:0:3}"
    done </tmp/test"$count" >/dev/null
}

var='0.1.2.3.4.5.6.7.8.9.'
count=100000
echo mkfile
mkfile "$count"
echo test_tr
time test_tr
echo test_sed
time test_sed
echo test_while
time test_while
echo hyperfine test_*
hyperfine -w 3 -r 1000 -i test_tr test_sed test_while
exit