我有一个shell脚本与这段代码:
var=`hg st -R "$path"`
if [ -n "$var" ]; then
echo $var
fi
但是条件代码总是执行，因为hg st总是打印至少一个换行符。
是否有一个简单的方法从$var中剥离空白(如PHP中的trim())?
or
有没有处理这个问题的标准方法?
我可以使用sed或AWK，但我认为有一个更优雅的解决方案来解决这个问题。
当前回答
还有一个单元测试的解决方案，它从stdin中删除$IFS，并适用于任何输入分隔符(甚至$'\0'):
ltrim()
{
# Left-trim $IFS from stdin as a single line
# $1: Line separator (default NUL)
local trimmed
while IFS= read -r -d "${1-}" -u 9
do
if [ -n "${trimmed+defined}" ]
then
printf %s "$REPLY"
else
printf %s "${REPLY#"${REPLY%%[!$IFS]*}"}"
fi
printf "${1-\x00}"
trimmed=true
done 9<&0
if [[ $REPLY ]]
then
# No delimiter at last line
if [ -n "${trimmed+defined}" ]
then
printf %s "$REPLY"
else
printf %s "${REPLY#"${REPLY%%[!$IFS]*}"}"
fi
fi
}
rtrim()
{
# Right-trim $IFS from stdin as a single line
# $1: Line separator (default NUL)
local previous last
while IFS= read -r -d "${1-}" -u 9
do
if [ -n "${previous+defined}" ]
then
printf %s "$previous"
printf "${1-\x00}"
fi
previous="$REPLY"
done 9<&0
if [[ $REPLY ]]
then
# No delimiter at last line
last="$REPLY"
printf %s "$previous"
if [ -n "${previous+defined}" ]
then
printf "${1-\x00}"
fi
else
last="$previous"
fi
right_whitespace="${last##*[!$IFS]}"
printf %s "${last%$right_whitespace}"
}
trim()
{
# Trim $IFS from individual lines
# $1: Line separator (default NUL)
ltrim ${1+"$@"} | rtrim ${1+"$@"}
}
其他回答
我总是用sed来做
var=`hg st -R "$path" | sed -e 's/ *$//'`
如果有更优雅的解决方案，我希望有人能发布出来。
Python有一个函数strip()，它的工作原理与PHP的trim()相同，因此我们可以使用一点内联Python来创建一个易于理解的实用程序:
alias trim='python -c "import sys; sys.stdout.write(sys.stdin.read().strip())"'
这将删除开头和结尾的空白(包括换行符)。
$ x=`echo -e "\n\t \n" | trim`
$ if [ -z "$x" ]; then echo hi; fi
hi
var=" a b "
echo "$(set -f; echo $var)"
>a b
#!/bin/bash
function trim
{
typeset trimVar
eval trimVar="\${$1}"
read trimVar << EOTtrim
$trimVar
EOTtrim
eval $1=\$trimVar
}
# Note that the parameter to the function is the NAME of the variable to trim,
# not the variable contents. However, the contents are trimmed.
# Example of use:
while read aLine
do
trim aline
echo "[${aline}]"
done < info.txt
# File info.txt contents:
# ------------------------------
# ok hello there $
# another line here $
#and yet another $
# only at the front$
#$
# Output:
#[ok hello there]
#[another line here]
#[and yet another]
#[only at the front]
#[]
var=' a b c '
trimmed=$(echo $var)
