linux – Shell =检查变量是否以#开头

发布时间：2020-12-13 18:26:56 所属栏目：Linux 来源：网络整理

导读：如果你能帮助我弄清楚如何确定变量的内容是否以井号开头,我将感激不尽： #!bin/sh myvar="#comment asfasfasdf"if [ myvar = #* ] 这不起作用. 谢谢！ JANS 解决方法一种方法是使用“子串扩展”来切掉变量内容的第一个字符： if [[ ${x:0:1} == '#' ]]then

如果你能帮助我弄清楚如何确定变量的内容是否以井号开头,我将感激不尽：

#!bin/sh    

myvar="#comment asfasfasdf"

if [ myvar = #* ]

这不起作用.

谢谢！

JANS

解决方法

一种方法是使用“子串扩展”来切掉变量内容的第一个字符：

if [[ ${x:0:1} == '#' ]]
then
    echo 'yep'
else
    echo 'nope'
fi

yep

从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.

编辑：

当然,如果您转义哈希,您的原始方法会正常工作：

$[[ '#snort' == #* ]]; echo $?
0

（编辑：李大同）

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