3.1.2 Bash - Quoting.md

3.1.2 Quoting(Escape)

Quoting is used to remove the special meaning of certain character or words to the shell

引号用于防止一些特殊的字符被 Shell 扩展

Quoting

Single Quotes

'(单引号)用于保留字符的字面意思，包括各种特殊字符($,*,\)

例如

[0x00@0xff1 tmp]$ a=1
[0x00@0xff1 tmp]$ echo "${a}"
1
[0x00@0xff1 tmp]$ echo '${a}'
${a}

需要注意的一点是单引号内不能出现单引号，即使单引号使用了 \ 来转义

[0x00@0xff1 tmp]$ echo '\''
> ^C

Double Quotes

“(双引号)保留大多数字符的字面意思，除了 $, ` , \ 会被 Bash 扩展

[0x00@0xff1 tmp]$ a=1
[0x00@0xff1 tmp]$ echo "${a}"
1
[0x00@0xff1 tmp]$ echo "`whoami`"
0x00

Escape

A non-quoted backslash \ is the Bash escape character. It preserves the literal value of the next character that follows

和其他大部分编程语言一样 \ (backslash) 都表示转义

[0x00@0xff1 tmp]$ a=1
[0x00@0xff1 tmp]$ echo "\${a}"
${a}
[0x00@0xff1 tmp]$ echo "${a}"
1