如果您能帮助我弄清楚如何确定变量的内容是否以井号开头,我将不胜感激:
#!bin/sh
myvar="#comment asfasfasdf"
if [ myvar = #* ]
这不起作用。
谢谢!
詹斯
答案1
如果你的原始方法逃脱哈希:
$ [[ '#snort' == \#* ]]; echo $?
0
另一种方法是使用“子字符串扩展”切掉变量内容的第一个字符:
if [[ ${x:0:1} == '#' ]]
then
echo 'yep'
else
echo 'nope'
fi
yep
来自 Bash 手册页:
${parameter:offset}
${parameter:offset:length}
Substring Expansion. Expands to up to length characters of
parameter starting at the character specified by offset. If
length is omitted, expands to the substring of parameter start-
ing at the character specified by offset. length and offset are
arithmetic expressions (see ARITHMETIC EVALUATION below).
length must evaluate to a number greater than or equal to zero.
If offset evaluates to a number less than zero, the value is
used as an offset from the end of the value of parameter. If
parameter is @, the result is length positional parameters
beginning at offset. If parameter is an array name indexed by @
or *, the result is the length members of the array beginning
with ${parameter[offset]}. A negative offset is taken relative
to one greater than the maximum index of the specified array.
Note that a negative offset must be separated from the colon by
at least one space to avoid being confused with the :- expan-
sion. Substring indexing is zero-based unless the positional
parameters are used, in which case the indexing starts at 1.
答案2
POSIX 兼容版本:
[ "${var%${var#?}}"x = '#x' ] && echo yes
或者:
[ "${var#\#}"x != "${var}x" ] && echo yes
或者:
case "$var" in
\#*) echo yes ;;
*) echo no ;;
esac
答案3
我知道这可能有点离经叛道,但对于这种事情,我宁愿使用 grep 或 egrep,而不是在 shell 中执行。这有点昂贵(我猜),但对我来说,这个解决方案的可读性弥补了这一点。当然,这只是个人喜好的问题。
所以:
myvar=" #comment asfasfasdf"
if ! echo $myvar | egrep -q '^ *#'
then
echo "not a comment"
else
echo "commented out"
fi
带或不带前导空格都可以。如果您还想考虑前导制表符,请使用 egrep -q '^[ \t]*#'。
答案4
这是另一种方法...
# assign to var the value of argument actual invocation
var=${1-"#default string"}
if [[ "$var" == "#"* ]]
then
echo "$var starts with a #"
fi
只需将内容复制粘贴到文件中,授予执行权限,然后观察其如何工作;)。
希望能帮助到你!
问候。