Trim()删除空白(以及制表符、不可打印字符;为了简单起见，我正在考虑使用空格)。我的解决方案是:

var="$(hg st -R "$path")" # I often like to enclose shell output in double quotes
var="$(echo "${var}" | sed "s/\(^ *\| *\$\)//g")" # This is my suggestion
if [ -n "$var" ]; then
 echo "[${var}]"
fi

sed命令只修剪开头和结尾的空白，但它也可以被输送到第一个命令，导致:

var="$(hg st -R "$path" | sed "s/\(^ *\| *\$\)//g")"
if [ -n "$var" ]; then
 echo "[${var}]"
fi

赋值函数忽略前导和后面的空格，因此可以用于修剪:

$ var=`echo '   hello'`; echo $var
hello

使用AWK:

echo $var | awk '{gsub(/^ +| +$/,"")}1'

要做到这一点，最简单和最便宜的方法是利用回声忽略空格。所以，就用

dest=$(echo $source)

例如:

> VAR="   Hello    World   "
> echo "x${VAR}x"
x   Hello    World   x
> TRIMD=$(echo $VAR)
> echo "x${TRIMD}x"
xHello Worldx

注意，这也将多个空格合并为一个空格。

如果启用了shop -s extglob，那么下面是一个简洁的解决方案。

这招对我很管用:

text="   trim my edges    "

trimmed=$text
trimmed=${trimmed##+( )} #Remove longest matching series of spaces from the front
trimmed=${trimmed%%+( )} #Remove longest matching series of spaces from the back

echo "<$trimmed>" #Adding angle braces just to make it easier to confirm that all spaces are removed

#Result
<trim my edges>

用更少的行数来获得相同的结果:

text="    trim my edges    "
trimmed=${${text##+( )}%%+( )}

使用这个简单的Bash参数展开:

$ x=" a z     e r ty "
$ echo "START[${x// /}]END"
START[azerty]END