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• 显示 /etc/inittab 文件中以 ‘#’ 号后跟着一个或多个空白字符开头并且之后是任意个非空白字符的行
• 查看/etc/inittab的内容

[04:16:42 rooter@C8-3-55 ~]#cat /etc/inittab# inittab is no longer used.## ADDING CONFIGURATION HERE WILL HAVE NO EFFECT ON YOUR SYSTEM.## Ctrl-Alt-Delete is handled by /usr/lib/systemd/system/ctrl-alt-del.target## systemd uses 'targets' instead of runlevels. By default, there are two main targets:## multi-user.target: analogous to runlevel 3# graphical.target: analogous to runlevel 5## To view current default target, run:# systemctl get-default## To set a default target, run:# systemctl set-default TARGET.target

• 显示#开头的注释行

[04:17:54 rooter@C8-3-55 ~]#cat /etc/inittab | grep ^## inittab is no longer used.## ADDING CONFIGURATION HERE WILL HAVE NO EFFECT ON YOUR SYSTEM.## Ctrl-Alt-Delete is handled by /usr/lib/systemd/system/ctrl-alt-del.target## systemd uses 'targets' instead of runlevels. By default, there are two main targets:## multi-user.target: analogous to runlevel 3# graphical.target: analogous to runlevel 5## To view current default target, run:# systemctl get-default## To set a default target, run:# systemctl set-default TARGET.target

• 敲错了啥都不显示
  没有加-E不支持正则表达式

[04:19:33 rooter@C8-3-55 ~]#cat /etc/inittab | grep ^#[[:blank:]]+[04:20:28 rooter@C8-3-55 ~]#cat /etc/inittab | grep '^#[[:blank:]]+'

• 显示#开头，其后是一个或多个空格的行

[04:20:38 rooter@C8-3-55 ~]#cat /etc/inittab | grep -E '^#[[:blank:]]+'# inittab is no longer used.# ADDING CONFIGURATION HERE WILL HAVE NO EFFECT ON YOUR SYSTEM.# Ctrl-Alt-Delete is handled by /usr/lib/systemd/system/ctrl-alt-del.target# systemd uses 'targets' instead of runlevels. By default, there are two main targets:# multi-user.target: analogous to runlevel 3# graphical.target: analogous to runlevel 5# To view current default target, run:# systemctl get-default# To set a default target, run:# systemctl set-default TARGET.target

• 显示#开头之后是1个或多个空格，之后是非空格的行

[04:21:06 rooter@C8-3-55 ~]#cat /etc/inittab | grep -E '^#[[:blank:]]+[^[:blank:]]+'# inittab is no longer used.# ADDING CONFIGURATION HERE WILL HAVE NO EFFECT ON YOUR SYSTEM.# Ctrl-Alt-Delete is handled by /usr/lib/systemd/system/ctrl-alt-del.target# systemd uses 'targets' instead of runlevels. By default, there are two main targets:# multi-user.target: analogous to runlevel 3# graphical.target: analogous to runlevel 5# To view current default target, run:# systemctl get-default# To set a default target, run:# systemctl set-default TARGET.target

• 显示#开头，之后是一个或多个空格，然后是非空格及任意字符的行

[04:21:56 rooter@C8-3-55 ~]#cat /etc/inittab | grep -E '^#[[:blank:]]+[^[:blank:]]+.*'# inittab is no longer used.# ADDING CONFIGURATION HERE WILL HAVE NO EFFECT ON YOUR SYSTEM.# Ctrl-Alt-Delete is handled by /usr/lib/systemd/system/ctrl-alt-del.target# systemd uses 'targets' instead of runlevels. By default, there are two main targets:# multi-user.target: analogous to runlevel 3# graphical.target: analogous to runlevel 5# To view current default target, run:# systemctl get-default# To set a default target, run:# systemctl set-default TARGET.target

问题：

• #号开头之后紧跟着1个以上空格的及任意字符的行，为啥把#后跟空行也过滤掉了？
  

回答：

• 看起来像#空行，但人家直接#$就结束了！
• 所以用一个以上blank就把看起来像空行的过滤掉了
  

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