Sed combined with regular expression hardening exercises

1. Delete all whitespace characters from the beginning of lines in the/etc/grub2.conf file that begin with whitespace

[[email protected] ~]# sed -r  ' s#^[[:space:]]+# #g '  /etc/grub2.cfg## do  NOT EDIT THIS FILE## It is automatically generated by  grub2-mkconfig using templates# from /etc/grub.d and settings from / etc/default/grub#### begin /etc/grub.d/00_header ## #set  pager=1if [ -s $ prefix/grubenv ]; thenload_envfiif [  "${next_entry}"  ] ; thenset  default= "${next_entry}" Set next_entry=save_env next_entryset boot_once=trueelseset default = "${saved_entry}" Fiif [ x "${feature_menuentry_id}"  = xy ]; thenmenuentry_id_ option= "--id" elsemenuentry_id_option= "" fiexport menuentry_id_optionif [  "${prev_saved_entry}"  ]; thenset saved_entry= "${prev_saved_entry}" save_env saved_entryset prev_saved_entry =save_env prev_saved_entryset&nBsp;boot_once=truefi 

2, delete all # and white-space characters at the beginning of the line beginning with # in the/etc/fstab file followed by at least one white-space character  

[[email protected] ~]# sed -r  ' s/^#[[:space:]]+//g '  /etc/fstab#/etc/fstabcreated  by anaconda on tue jul 19 14:39:24 2016#accessible filesystems,  by reference, are maintained under  '/dev/disk ' see man pages  Fstab (5),  findfs (8),  mount (8)  and/or blkid (8)  for more info#uuid= f83c52ce-5740-4f02-bb87-6e190360dc30 /                        xfs      defaults  0 0uuid=c98144e4-d1b4-45b1-bb22-3112420ea487 /boot                    xfs      defaults  0 0UUID=dbf5c483-133e-4888-bbb1-a9622d83a930 swap                     swap    defaults   0 0#end[[email protected] ~]#

2.1, delete all # and white space characters beginning with # at the beginning of the line in the/etc/fstab file followed by at least one white-space character, and delete the line followed by # that is full of whitespace characters

[[email protected] ~]# sed -r -e  ' s/^#[[:space:]]+//g '  -e  '/^#/d '  /etc/fstab/etc/fstabCreated by anaconda on Tue Jul 19 14:39:24  2016accessible filesystems, by reference, are maintained under  '/dev/disk ' See man pages fstab (5),  findfs (8),  mount (8)  and/or blkid (8)  for  more infouuid=f83c52ce-5740-4f02-bb87-6e190360dc30 /                        xfs      defaults  0 0UUID=c98144e4-d1b4-45b1-bb22-3112420ea487 /boot                    xfs      defaults  0 0uuid=dbf5c483-133e-4888-bbb1-a9622d83a930 swap                     swap     defaults  0 0[[email protected] ~]#

3. Add # At the beginning of each line of/etc/issue

[Email protected] ~]# cat-n/etc/issue 1\s 2Kernel \ r on a \m 3[[email protected] ~]# sed-r ' [email Protec Ted] (. *) @#&@g '/etc/issue#\s#kernel \ r on an \m#[[email protected] ~]# sed-r ' [email protected] (. *) @#\[email PROTECTE d] '/etc/issue#\s#kernel \ r on an \m#[[email protected] ~]# sed-r ' [email protected]^@#@g '/etc/issue#\s#kernel \ R on an \m#[[email protected] ~]#

4. Add # to the beginning of the line in the/etc/fstab file that does not begin with #

[[email protected] ~]# sed -r  ' s/^[^#]/#/g '  /etc/fstab## /etc/fstab#  Created by anaconda on tue jul 19 14:39:24 2016## accessible  filesystems, by reference, are maintained under  '/dev/disk ' # see  man pages fstab (5),  findfs (8),  mount (8)  and/or blkid (8)  for more  info# #UID =f83c52ce-5740-4f02-bb87-6e190360dc30 /                        xfs      defaults#UID=c98144e4-d1b4-45b1-bb22-3112420ea487 /boot                    xfs      defaults#UID=dbf5c483-133e-4888-bbb1-a9622d83a930 swap             &nbSp;       swap    defaults#end[[email protected]  ~]#

5, processing/etc/fstab path, use sed command to take out its directory name and base name

[[email protected] packages]# Cd[[email protected] ~]# echo "/etc/hosts" |sed-r ' s#/.*/([^/]+] #\1#g ' Hosts[[email Protected] ~]# echo "/etc/hosts" |sed-r ' s# (/.*/) [^/]+/?#\1#g '/etc/[[email protected] ~]# echo "/etc/issue" |sed-r ' s# (. * /)([^/]+/?) $#\1#g '/etc/[[email protected] ~]# echo "/etc/issue" |sed-r ' s# (. */) ([^/]+/?) $#\2#g ' Issue[[email protected] ~]#

6. Use SED to remove the IPv4 address of the ifconfig command

[Email protected] ~]# ifconfig |sed-n 2p inet 192.168.226.138 netmask 255.255.255.0 broadcast 192.168.226.255[[ Email protected] ~]# ifconfig |sed-n 2p|sed-r ' s/.*net//g ' 192.168.226.138 netmask 255.255.255.0 broadcast 192.168.226  .255[[email protected] ~]# ifconfig |sed-n 2p|sed-r ' s/.*net//g ' |sed-r ' s/net.*//g ' 192.168.226.138[[email protected] ~]# ifconfig |sed-nr ' 2s#^.*net (. *) NETM.*$#\1#GP ' 192.168.226.138[[email protected] ~]#

7. Statistics of all RPM files in the package directory on the CentOS installation CD. Number of repetitions of the second-to-last field

[email protected] packages]# ls *.rpm |sed-r ' s/^.*\. (. *) \.rpm/\1/g ' |sort |uniq-c |sort-i686 2938 noarch 4069 x86_64[[email protected] packages]# ls *.rpm |rev |cu t-d.-f2 |sort|uniq-c|uniq 4069 46_68x 686i 2938 hcraon[[email protected] packages]#

This article is from "Wake up your not alarm clock but dream" blog, please be sure to keep this source http://purify.blog.51cto.com/10572011/1836292

Sed combined with regular expression hardening exercises