关于使用grep的问题

Question

 127.0.0.1 - - [08/Mar/2011:00:26:27 +0530] "HEAD /sk/ HTTP/1.1" 200 169 "-" "Python-urllib/2.6"
127.0.0.1 - - [08/Mar/2011:00:26:27 +0530] "HEAD /sk/.treeinfo HTTP/1.1" 404 182 "-" "Python-urllib/2.6"
127.0.0.1 - - [08/Mar/2011:00:26:27 +0530] "HEAD /sk/Fedora HTTP/1.1" 404 182 "-" "Python-urllib/2.6"
127.0.0.1 - - [08/Mar/2011:00:26:27 +0530] "HEAD /sk/Server HTTP/1.1" 404 182 "-" "Python-urllib/2.6"
127.0.0.1 - - [08/Mar/2011:00:26:27 +0530] "HEAD /sk/Client HTTP/1.1" 404 182 "-" "Python-urllib/2.6"
127.0.0.1 - - [08/Mar/2011:00:26:27 +0530] "HEAD /sk/RedHat HTTP/1.1" 404 182 "-" "Python-urllib/2.6"
127.0.0.1 - - [08/Mar/2011:00:26:27 +0530] "HEAD /sk/CentOS HTTP/1.1" 404 182 "-" "Python-urllib/2.6"
127.0.0.1 - - [08/Mar/2011:00:26:27 +0530] "HEAD /sk/SL HTTP/1.1" 404 182 "-" "Python-urllib/2.6"
127.0.0.1 - - [08/Mar/2011:00:26:27 +0530] "HEAD /sk/directory.yast HTTP/1.1" 404 182 "-" "Python-urllib/2.6"
127.0.0.1 - - [08/Mar/2011:00:26:27 +0530] "HEAD /sk/current/images/MANIFEST HTTP/1.1" 404 182 "-" "Python-urllib/2.6"
127.0.0.1 - - [08/Mar/2011:00:26:27 +0530] "HEAD /sk/images/daily/MANIFEST HTTP/1.1" 404 182 "-" "Python-urllib/2.6"
127.0.0.1 - - [08/Mar/2011:00:26:27 +0530] "HEAD /sk/boot/platform/i86xpv/kernel/unix HTTP/1.1" 404 182 "-" "Python-urllib/2.6"
127.0.0.1 - - [08/Mar/2011:00:26:27 +0530] "HEAD /sk/platform/i86xpv/kernel/unix HTTP/1.1" 404 182 "-" "Python-urllib/2.6"
127.0.0.1 - - [08/Mar/2011:00:26:27 +0530] "HEAD /sk/STARTUP/XNLOADER.SYS HTTP/1.1" 404 182 "-" "Python-urllib/2.6"
127.0.0.1 - - [08/Mar/2011:00:26:27 +0530] "HEAD /sk/images/xen/vmlinuz HTTP/1.1" 404 182 "-" "Python-urllib/2.6"
127.0.0.1 - - [08/Mar/2011:00:26:27 +0530] "HEAD /sk/images/boot.iso HTTP/1.1" 404 182 "-" "Python-urllib/2.6"
127.0.0.1 - - [08/Mar/2011:00:26:27 +0530] "HEAD /sk/boot/boot.iso HTTP/1.1" 404 182 "-" "Python-urllib/2.6"
127.0.0.1 - - [08/Mar/2011:00:26:27 +0530] "HEAD /sk/current/images/netboot/mini.iso HTTP/1.1" 404 182 "-" "Python-urllib/2.6"
127.0.0.1 - - [08/Mar/2011:00:26:27 +0530] "HEAD /sk/install/images/boot.iso HTTP/1.1" 404 182 "-" "Python-urllib/2.6"
127.0.0.1 - - [08/Mar/2011:00:26:35 +0530] "HEAD /sk/ HTTP/1.1" 200 169 "-" "Python-urllib/2.6"
127.0.0.1 - - [08/Mar/2011:00:26:35 +0530] "HEAD /sk/.treeinfo HTTP/1.1" 404 182 "-" "Python-urllib/2.6"
127.0.0.1 - - [08/Mar/2011:00:26:35 +0530] "HEAD /sk/Fedora HTTP/1.1" 404 182 "-" "Python-urllib/2.6"
127.0.0.1 - - [08/Mar/2011:00:26:35 +0530] "HEAD /sk/Server HTTP/1.1" 404 182 "-" "Python-urllib/2.6"
127.0.0.1 - - [08/Mar/2011:00:26:35 +0530] "HEAD /sk/Client HTTP/1.1" 404 182 "-" "Python-urllib/2.6"
127.0.0.1 - - [08/Mar/2011:00:26:35 +0530] "HEAD /sk/RedHat HTTP/1.1" 404 182 "-" "Python-urllib/2.6"
127.0.0.1 - - [08/Mar/2011:00:26:35 +0530] "HEAD /sk/CentOS HTTP/1.1" 404 182 "-" "Python-urllib/2.6"
127.0.0.1 - - [08/Mar/2011:00:26:35 +0530] "HEAD /sk/SL HTTP/1.1" 404 182 "-" "Python-urllib/2.6"
127.0.0.1 - - [08/Mar/2011:00:26:35 +0530] "HEAD /sk/directory.yast HTTP/1.1" 404 182 "-" "Python-urllib/2.6"
127.0.0.1 - - [08/Mar/2011:00:26:35 +0530] "HEAD /sk/current/images/MANIFEST HTTP/1.1" 404 182 "-" "Python-urllib/2.6" 

我有一个上面结构的文件,它是名称log.txt.现在我做

 cat log.txt | grep '[*]' 

那时我没有输出

 cat log.txt | grep '\[* \]' 

再次没有输出,但是当我做的时候

 cat log.txt | grep '\[.*\]'

然后有输出这是如何工作的？

UPTADE

我基本上试图在上面的日志中查找时间戳.

Answer 1

cat log.txt | grep '[*]' 

此命令行在文件中搜索log.txt包含*其中一行的行.由于输入中的所有行都没有*得到任何结果.请注意,[..]在正则表达式中称为一个字符类,它匹配其中的任何字符.

cat log.txt | grep '\[* \]' 

此命令行在文件中搜索具有零个或多个文字的行,[后跟一个空格,后跟一个文字].你再也没有这样的台词.在这里,你已经逃脱了[和].这使得它们非特殊.所以他们不再形成一个角色类,而是按字面意思对待.

cat log.txt | grep '\[.*\]'

这个搜索[后跟任何(.*)后跟a的行].由于你有这样的线,你得到输出.

最后

 cat file | grep pattern

被称为无用的猫,可以写成:

grep pattern file