CentOS 6 和CentOS 7 中grep命令的递归参数差异
习惯于用grep命令检索文件中是否包含某关键字,对某个目录中所有文件内关键字的检索,习惯于用“-r”参数操作,偶然发现这个参数在CentOS 6和CentOS 7下的意义已经不同了。
先看CentOS 7场景:
~ $ cat /etc/centos-release CentOS Linux release 7.2.1511 (Core) ~ $ ls -al /usr/local/nginx/conf/include/ total 24 drwxr-xr-x 2 root root 4096 Mar 6 2019 ./ drwxr-xr-x 6 root root 4096 Mar 6 2019 ../ -rwxr-xr-x 1 root root 672 Mar 6 2019 default_server.conf* lrwxrwxrwx 1 root root 41 Dec 18 2017 j.conf -> /tmp/j.nginx* ~ $ grep -r -i -P '^([ \t]*)ssl_certificate' /usr/local/nginx/conf/include/ /usr/local/nginx/conf/include/default_server.conf: ssl_certificate certs/default_server.crt; /usr/local/nginx/conf/include/default_server.conf: ssl_certificate_key certs/default_server.key; ~ $ grep -r -i -P '^([ \t]*)ssl_certificate' /usr/local/nginx/conf/include/j.conf ssl_certificate certs/quwenqing.com.crt; ssl_certificate_key certs/quwenqing.com.key;
j.conf文件中明明有ssl_certificate关键字,对目录级检索,却没有找到。
再看一下CentOS 6场景
~ $ cat /etc/centos-release CentOS release 6.8 (Final) ~ $ ls -al /usr/local/nginx/conf/include/ total 24 drwxr-xr-x 2 root root 4096 Mar 6 2019 ./ drwxr-xr-x 6 root root 4096 Mar 6 2019 ../ -rwxr-xr-x 1 root root 672 Mar 6 2019 default_server.conf* lrwxrwxrwx 1 root root 41 Dec 18 2017 j.conf -> /tmp/j.nginx* ~ $ grep -r -i -P '^([ \t]*)ssl_certificate' /usr/local/nginx/conf/include/ /usr/local/nginx/conf/include/default_server.conf: ssl_certificate certs/default_server.crt; /usr/local/nginx/conf/include/default_server.conf: ssl_certificate_key certs/default_server.key; /usr/local/nginx/conf/include/j.conf: ssl_certificate certs/quwenqing.com.crt; /usr/local/nginx/conf/include/j.conf: ssl_certificate_key certs/quwenqing.com.key;
可以在目录级检索中正确查找到关键字。
仔细看上面场景,同样执行 grep -r -i -P '^([ \t]*)ssl_certificate' /usr/local/nginx/conf/include/ 这个命令CentOS 6中可以查到软链文件中的关键字,而CentOS 7中却没有查询到。
最好的解惑方式是看帮助手册,果然有收获。
## CentOS 6 ~ $ man grep -R, -r, --recursive Read all files under each directory, recursively; this is equivalent to the -d recurse option. ## CentOS 7 ~ $ man grep -r, --recursive Read all files under each directory, recursively, following symbolic links only if they are on the command line. This is equivalent to the -d recurse option. -R, --dereference-recursive Read all files under each directory, recursively. Follow all symbolic links, unlike -r.
原来,在CentOS 7中对-r、-R参数功能做了拆分,适用于不同的应用场景。