trim spaces from a shell string

how to remove leading and trailing spaces from a shell variable?
如何删除shell字符串变量中的前缀的和后缀的空格?

var="   hello world!    "
echo "var=\"$var\""

var="   hello world!    "

1. echo

newvar=$(echo $var)
echo "newvar=\"$newvar\""

newvar="hello world!"

2. Parameter Substitution

newvar=${var#"${var%%[![:blank:]]*}"}
newvar=${newvar%"${newvar##*[![:blank:]]}"}
echo "newvar=\"$newvar\""

newvar="hello world!"

3. Pattern Matching

shopt -s extglob
newvar=${var##+( )}
newvar=${newvar%%+( )}
shopt -u extglob
echo "newvar=\"$newvar\""

newvar="hello world!"

4. sed

newvar=$(echo "$var"|sed 's/\(^[[:blank:]]\+\|[[:blank:]]\+$\)//g')
echo "newvar=\"$newvar\""

newvar="hello world!"

5. awk

newvar=$(echo "$var"|awk 'gsub(/^[[:blank:]]+|[[:blank:]]+$/,"")')
echo "newvar=\"$newvar\""

newvar="hello world!"

-fin-