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Monday, November 23, 2009

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-

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