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sed sed中文命令基础 good reference
• sed替换变量${var}用双引号""; 变量$ or ${} are the same;
• sed replace using s:$old:$new: pattern --
• The syntax of the s (as in substitute) command is ‘s/regexp/replacement/flags’. The / characters may be uniformly replaced by any other single character within any given s command. The / character (or whatever other character is used in its stead) can appear in the regexp or replacement only if it is preceded by a \ character.
• .* 多个字符
• e.g.: sed -e "s:installationRoot\">.*<:installationRoot\">$installLocation<:" \ -e "s:environmentName\">.*<:environmentName\">$envName<:" \ filetoreplace-bk.txt > filetoreplace.txt

• shell变量是全局的
• 引用命令行用``
• 调用当前时间：date + (format)
• After each command, the exit code can be found in the $? Exit status
• man bash --> get $?
• 接收参数方法： Shell预定义变量有:

$# 位置参数的数量.

$* 所有位置参数的内容.

$? 命令执行后返回的状态. A successful command returns a 0

$$ 当前进程的进程号.

$! 后台运行的最后一个进程号.

$0 当前执行的进程名.

$@ 类似java得所有得自变量数组

• >2>&1 -> & is the syntax to redirect a stream to another file descriptor - 0 is stdin. 1 is stdout. 2 is stderr.

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