Sed replacement and modification of link files

Sed replacement and modification of link files

1. Sed replacement and modification of link files
   
2. 
   
3. # System and version
   
4. [Root @ localhost ~] # Cat/etc/redhat-release
   
5. CentOS release 6.8 (Final)
   
6. [Root @ localhost ~] # Sed -- version
   
7. GNU sed version 4.2.1
   
8. Copyright (C) 2009 Free Software Foundation, Inc.
   
9. This is free software; see the source for copying conditions. There is NO
   
10. Warranty; not even for MERCHANTABILITY or fitness for a particle PURPOSE,
    
11. To the extent permitted by law.
    
12. 
    
13. Because sed-I/etc/sysconfig/selinux (The selinux file is a soft link of/etc/selinux/config), SELINUX is not closed after the configuration file is restarted, only then can we find that the sed-I cannot directly modify the soft link file. The following is the consequence of my modifications:
    
14. [Root @ localhost ~] # Ll/etc/sysconfig/selinux
    
15. Lrwxrwxrwx. 1 root 17 Dec 20 :31/etc/sysconfig/selinux-> ../selinux/config
    
16. [Root @ localhost ~] # Ll/etc/selinux/config
    
17. -Rw-r --. 1 root 458 Dec 20 :31/etc/selinux/config
    
18. 
    
19. 
    
20. [Root @ localhost ~] # Sed-I "s/SELINUX = enforcing/SELINUX = disabled/g"/etc/sysconfig/selinux
    
21. [Root @ localhost ~] # Ll/etc/sysconfig/selinux
    
22. -Rw-r --. 1 root 457 Dec 22 19: 18/etc/sysconfig/Selin
    
23. 
    
24. We found that the linked file is no longer a linked file. Later we checked the sed -- help option and found the following options.
    
25. 
    
26. -- Follow-symlinks
    
27. Follow symlinks when processing in place; hard links will still be broken.
    
28. 
    
29. -I [SUFFIX], -- in-place [= SUFFIX]
    
30. Edit files in place (makes backup if extension supplied). The default operation mode is
    
31. Break symbolic and hard links. This can be changed with -- follow-symlinks and -- copy.
    
32. 
    
33. -C, -- copy
    
34. Use copy instead of rename when shuffling files in-I mode. While this will avoid breaking
    
35. Links (symbolic or hard), the resulting editing operation is not atomic. This is rarely
    
36. Desired mode; -- follow-symlinks is usually enough, and it is both faster and more secure.
    
37. 
    
38. 
    
39. 
    
40. # Test
    
41. [Root @ localhost ~] # Echo "test"> test
    
42. [Root @ localhost ~] # Ln-s test-zsq
    
43. [Root @ localhost ~] # Ll-I test-zsq # Link file
    
44. 260727 lrwxrwxrwx. 1 root 4 Dec 22 test-zsq-> test
    
45. [Root @ localhost ~] # Cat test-zsq
    
46. Test
    
47. 
    
48. # If you delete the link directly, the linked file will become invalid.
    
49. [Root @ localhost ~] # Sed-I "s/test // g" test-zsq
    
50. [Root @ localhost ~] # Ll-I test-zsq
    
51. 260726-rw-r --. 1 root 1 Dec 22 19: 29 test-zsq
    
52. 
    
53. # Re-add and re-test, and add the-c option
    
54. [Root @ localhost ~] # Rm-rf test-zsq
    
55. [Root @ localhost ~] # Ln-s test-zsq
    
56. [Root @ localhost ~] # Ll-I test-zsq
    
57. 260726 lrwxrwxrwx. 1 root 4 Dec 22 test-zsq-> test
    
58. [Root @ localhost ~] # Echo "test"> test
    
59. [Root @ localhost ~] # Sed-I-c '/test/d' test-zsq
    
60. [Root @ localhost ~] # Ll-I test-zsq
    
61. 260726 lrwxrwxrwx. 1 root 4 Dec 22 test-zsq-> test
    
62. 
    
63. # -- Follow-symlinks Option
    
64. [Root @ localhost ~] # Rm-rf test-zsq
    
65. [Root @ localhost ~] # Ln-s test-zsq
    
66. [Root @ localhost ~] # Echo "test"> test
    
67. [Root @ localhost ~] # Cat test
    
68. Test
    
69. [Root @ localhost ~] # Sed-I -- follow-symlinks '/test/d' test
    
70. [Root @ localhost ~] # Ls-l test-zsq
    
71. Lrwxrwxrwx. 1 root 4 Dec 22 19: 50 test-zsq-> test
    
72. [Root @ localhost ~] # Cat test
    
73. 
    
74. 
    
75. -- Follow-symlinks is faster and safer than-c.
    
76. -C, -- copy
    
77. Use copy instead of rename when shuffling files in-I mode.
    
78. While this will avoid breaking links (symbolic or hard),
    
79. Resulting editing operation is not atomic. This is rarely
    
80. The desired mode; -- follow-symlinks is usually enough, and
    
81. It is both faster and more secure.
    
82. 
    
83. 
    
84. The connection file/etc/rc. local is also a soft connection of/etc/rc. d/rc. local. Use sed to add or delete the startup service.
    
85. It is possible that the configured link file becomes invalid and the service cannot be started.
    
86. 
    
87. 
    
88. Running the same operations in the centos 5.x series does not produce similar results.
    
89. It is found that the sed version is different, and the centos 5 series still uses the old version of sed, without the -- follow-symlinks similar options.
    
90. 
    
91. [Root @ DNS ~] # Sed -- version
    
92. GNU sed version 4.1.5
    
93. Copyright (C) 2003 Free Software Foundation, Inc.
    
94. This is free software; see the source for copying conditions. There is NO
    
95. Warranty; not even for MERCHANTABILITY or fitness for a particle PURPOSE,
    
96. To the extent permitted by law.
    
97. [Root @ DNS ~] # Sed -- help
    
98. Usage: sed [OPTION]... {script-only-if-no-other-script} [input-file]...
    
99. 
    
100. -N, -- quiet, -- silent
     
101. Suppress automatic printing of pattern space
     
102. -E script, -- expression = script
     
103. Add the script to the commands to be executed
     
104. -F script-file, -- file = script-file
     
105. Add the contents of script-file to the commands to be executed
     
106. -I [SUFFIX], -- in-place [= SUFFIX]
     
107. Edit files in place (makes backup if extension supplied)
     
108. -C, -- copy
     
109. Use copy instead of rename when shuffling files in-I mode
     
110. (Avoids change of input file ownership)
     
111. -L N, -- line-length = N
     
112. Specify the desired line-wrap length for the 'l' command
     
113. -- Posix
     
114. Disable all GNU extensions.
     
115. -R, -- regexp-extended
     
116. Use extended regular expressions in the script.
     
117. -S, -- separate
     
118. Consider files as separate rather than as a single continuous
     
119. Long stream.
     
120. -U, -- unbuffered
     
121. Load minimal amounts of data from the input files and flush
     
122. The output buffers more often
     
123. -- Help display this help and exit
     
124. -- Version output version information and exit