Trim whitespaces from a string with pure bash

trim-string.sh

trim_l() {
    local str="$1"
    if [[ $str =~ ^[[:space:]]*(|[^[:space:]].*)$ ]]; then
        str="${BASH_REMATCH[1]}"
    fi
    echo "$str"
}

trim_r() {
    local str="$1"
    if [[ $str =~ ^(|.*[^[:space:]])[[:space:]]*$ ]]; then
        str="${BASH_REMATCH[1]}"
    fi
    echo "$str"
}

trim() {
    local str="$1"
    if [[ $str =~ ^[[:space:]]*(|[^[:space:]]|[^[:space:]].*[^[:space:]])[[:space:]]*$ ]]; then
        str="${BASH_REMATCH[1]}"
    fi
    echo "$str"
}

result_ok=0
result_fail=0
test() {
    local method="$1"
    local test_data="$2"
    local expected="$3"

    local result="$($method "$test_data")"

    if [[ $result == $expected ]]; then
        echo "OK:   ${method}:   |${test_data}|   =>   |${result}|"
        let result_ok++
        return
    fi

    echo "FAIL: ${method}:   |${test_data}|   =>   |${result}|   (expected: |${expected}|)"
    let result_fail++
    return 1
}

test trim   "" ""
test trim_l "" ""
test trim_r "" ""
echo ""

test trim   "a" "a"
test trim_l "a" "a"
test trim_r "a" "a"
echo ""

test trim   "ab" "ab"
test trim_l "ab" "ab"
test trim_r "ab" "ab"
echo ""

test trim   "abc" "abc"
test trim_l "abc" "abc"
test trim_r "abc" "abc"
echo ""

test trim   "abcd" "abcd"
test trim_l "abcd" "abcd"
test trim_r "abcd" "abcd"
echo ""

test trim   "  abcd" "abcd"
test trim_l "  abcd" "abcd"
test trim_r "  abcd" "  abcd"
echo ""

test trim   "abcd  " "abcd"
test trim_l "abcd  " "abcd  "
test trim_r "abcd  " "abcd"
echo ""

test trim   "  abcd   " "abcd"
test trim_l "  abcd   " "abcd   "
test trim_r "  abcd   " "  abcd"
echo ""

test trim   "  ab cd   " "ab cd"
test trim_l "  ab cd   " "ab cd   "
test trim_r "  ab cd   " "  ab cd"
echo ""

test trim   "  ab x   y cd   " "ab x   y cd"
test trim_l "  ab x   y cd   " "ab x   y cd   "
test trim_r "  ab x   y cd   " "  ab x   y cd"
echo ""

echo "Result:"
echo "  OK:   ${result_ok}"
echo "  FAIL: ${result_fail}"