string 如何在 Bash 或 UNIX shell 中检查字符串中的第一个字符？
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How to check the first character in a string in Bash or UNIX shell?
提问by canecse
I'm writing a script in UNIX where I have to check whether the first character in a string is "/" and if it is, branch.
我正在 UNIX 中编写一个脚本，我必须检查字符串中的第一个字符是否为“/”，如果是，则进行分支。
For example I have a string:
例如我有一个字符串：
/some/directory/file
I want this to return 1, and:
我希望它返回 1，并且：
[email protected]:/some/directory/file
to return 0.
返回 0。
回答by user000001
Many ways to do this. You could use wildcards in double brackets:
有很多方法可以做到这一点。您可以在双括号中使用通配符：
str="/some/directory/file"
if [[ $str == /* ]]; then echo 1; else echo 0; fi
You can use substring expansion:
您可以使用子字符串扩展：
if [[ ${str:0:1} == "/" ]] ; then echo 1; else echo 0; fi
Or a regex:
或正则表达式：
if [[ $str =~ ^/ ]]; then echo 1; else echo 0; fi
回答by konsolebox
Consider the case statement as well which is compatible with most sh-based shells:
还要考虑与大多数基于 sh 的 shell 兼容的 case 语句：
case $str in
/*)
echo 1
;;
*)
echo 0
;;
esac
回答by devnull
$ foo="/some/directory/file"
$ [ ${foo:0:1} == "/" ] && echo 1 || echo 0
1
$ foo="[email protected]:/some/directory/file"
$ [ ${foo:0:1} == "/" ] && echo 1 || echo 0
0
