Nine shell solutions to practical Linux O & M Problems

Source: Old Boy's Linux blog Author: Old Boy

The problem is:
4) known: the content of/etc/hosts is
192.168.1.11 oldboy11.etiantian.org
192.168.1.21 oldboy21.etiantian.org
192.168.1.31 oldboy31.etiantian.org

#192.168.1.111 oldboy111.etiantian.org
Please use shell scripts. How can I find the unique hostname in/etc/hosts after entering the IP address?
Answer:
Method 1) script Filtering# Cat judgehost. Sh

1. #! /Bin/bash
2. echo "Please input IP Address:"
3. Read ip address
4. [-n "'grep" $ IP "/etc /hosts' ".
5. echo "the hostname is: 'grep " $ IP "/etc/hosts | awk '{print $2} ''" | \
6. echo "the IP is invalid"

Tip:
1) This is an implementation syntax for grep filtering and conditional judgment:
2) The condition judgment syntax is [-n "DDD"] & Echo 1 | Echo 0
3) [-n "'grep" $ IP "/etc/hosts. Here, we want to exclude the following duplicates.
192.168.1.11 oldboy11.etiantian.org
192.168.1.111 oldboy111.etiantian.org
---------------- I am a separator for each method ---------------
Method 2) exact script matching:

2. #! /Bin/bash
4. # Author oldboy
6. # QQ 1, 31333741
8. # Judge Input
10. If [$ #-ne 1]
12. Then 
14. Echo"Input error! " 
16. Exit 1
18. Fi
20.  
22. Flag = 0
24. Exec</Etc/hosts
26. WhileReadLine
28. Do
30. If ["$1"="'Echo $ Line | awk' {print $1 }''"]
32. Then 
34. Flag = 1
36. Echo"The $1's hostname is 'echo $ Line | awk '{print $2 }''"
38. Break;
40. Fi
42. Done
44. [$ Flag-EQ 0] & Echo"Sorrry, not find $1's hostname! " 
46.  

Tip: For this question, please learn how to use while and how to set flag.

Execution result:
# Sh oldboy. Sh 192.168.1.11
The 192.168.1.11's hostname is oldboy11.etiantian.org
# Sh oldboy. Sh 192.168.1.21
The 192.168.1.21's hostname is oldboy21.etiantian.org
# Sh oldboy. Sh 192.168.1.311
Sorrry, not find 192.168.1.311's hostname!
---------------- I am a separator for each method ---------------

Note: In the following method, the old boys and teachers use different awk methods to implement the same function in large numbers to tell you That awk is very powerful, I hope that the students will be proficient in teaching.

Method 3) awk exact match:
Preparation:
# Tail-4/etc/hosts
192.168.1.11 oldboy11.etiantian.org
192.168.1.111 oldboy111.etiantian.org
192.168.1.21 oldboy21.etiantian.org
192.168.1.31 oldboy31.etiantian.org
Script:

1. [Root @ old_boy Scripts] # Cat awkhost1.sh
2. Awk'Begin{ A = "'$1'"} {If ($1 = A) Print $2 ;}'/Etc/hosts

Execution result:
# Sh awkhost1.sh 192.168.1.21
Oldboy21.etiantian.org
# Sh awkhost1.sh 192.168.1.31
Oldboy31.etiantian.org
# Sh awkhost1.sh 192.168.1.11
Oldboy11.etiantian.org
Tip: Pay attention to the usage of a = "'$ 1'". $1 is a command line parameter. AwkProgramA = "'$1 '".
---------------- I am a separator for each method ---------------
Method 4) awk exact match

1. [Root @ old_boy Scripts] # Cat awkhost2.sh
2. Awk'{If ($1 = "'$1'") Print $2 }'/Etc/hosts

Execution result:
# Awkhost2.sh 192.168.1.11
Oldboy11.etiantian.org
# Awkhost2.sh 192.168.1.21
Oldboy21.etiantian.org
# Awkhost2.sh 192.168.1.311
---------------- I am a separator for each method ---------------
Method 5) awk Filtering

1. # Cat awkhost4.sh
2. Awk'/'"$ {1 }"'/''{Print $2 }'/Etc/hosts
3. Execution result:
4. # Awkhost4.sh 192.168.1.21
5. Oldboy21.etiantian.org
6. # Awkhost4.sh 192.168.1.11
7. Oldboy11.etiantian.org
8. # Awkhost4.sh 192.168.1.31
9. Oldboy31.etiantian.org
10. Tip: apart from the syntax, this question is learned, that is, when filtering, passing parameters should end with a space to filter out duplicate IP addresses.
11. For example:
12. 192.168.1.11 oldboy11.etiantian.org
13. 192.168.1.111 oldboy111.etiantian.org

---------------- I am a separator for each method ---------------
Method 6) awk Filtering

2. # Cat awkhost5.sh
4. Awk'{If ($1 ~ /'$1'/) Print $2 }'/Etc/hosts # print the second column if the first column of the file contains the first parameter character of the command line
6. Execution result:
8. # Awkhost5.sh 192.168.1.31
10. Oldboy31.etiantian.org
12. # Awkhost5.sh 192.168.1.11
14. Oldboy11.etiantian.org
16. Oldboy111.etiantian.org------> A bug exists here. 
18. # Awkhost5.sh 192.168.1.21
20. Oldboy21.etiantian.org
22. Fix bugs after improvement:
24. # Cat awkhost5-1.sh
26. Awk'{If ($1 ~ /'$1'/) Print $2 }'/Etc/hosts ==> it is incorrect to add spaces above.
28. # Cat awkhost5-1.sh
30. Awk'{If ($1 ~ /'$1'$/) Print $2 }'/Etc/hosts # Add a regular expression $
32. Execution result:
34. # Awkhost5-1.sh 192.168.1.21
36. Oldboy21.etiantian.org
38. # Awkhost5-1.sh 192.168.1.11
40. Oldboy11.etiantian.org
42. # Awkhost5-1.sh 192.168.1.31
44. Oldboy31.etiantian.org

---------------- I am a separator for each method ---------------
Method 7) awk-V exact match
 

2. Command Line test:
4. # Awk-V p = 192.168.1.21'$1 = P {print $2 }'/Etc/hosts
6. Oldboy21.etiantian.org
8. # Awk-V p = 192.168.1.11'$1 = P {print $2 }'/Etc/hosts
10. Oldboy11.etiantian.org
12. # Awk-V p = 192.168.1.11'$1 = P {print $2 }'/Etc/hosts
14. Oldboy11.etiantian.org
16. Actual script:
18. # Cat awkhost6.sh
20. #! /Bin/bash
22. # P = $1
24. # Awk-V p ="$ P" '$1 = P {print $2 }'/Etc/hosts
26. Awk-V p ="$1" '$1 = P {print $2 }'/Etc/hosts

execution result:
# sh awkhost6.sh 192.168.1.11
oldboy11.etiantian.org
# sh awkhost6.sh 192.168.1.21
oldboy21.etiantian.org
tip:
1) if the parameter is not an awk program, P = "$1"
2) man awk
-V Var = Val
-- assign Var = Val
assign the value Val to the variable VAR, before execution of the program begins. such vari-
able values are available to the begin block of an awk program.
---------------- I am the separator of each method ---------------
Method 8: simple Method of exact match

1. # Cat awkhost9.sh
2. Awk'$1 = "'$1'"{Print $2 }'/Etc/hosts
3. Execution result:
4. # Sh awkhost9.sh 192.168.1.11
5. Oldboy11.etiantian.org
6. # Sh awkhost9.sh 192.168.1.21
7. Oldboy21.etiantian.org
8. # Sh awkhost9.sh 192.168.1.31
9. Oldboy31.etiantian.org
10. Note: here, the old boys and teachers use different awk methods to implement the same function. It is very powerful,
11. I hope that the students will be proficient in teaching.

---------------- I am a separator for each method ---------------
Method 9: an immature Implementation Method for students

2. #! /Bin/bash
4. B =/$ PWD/wang.txt
6. Echo-n"Plase input IP :" 
8. ReadA
10. If [$ A ="192.168.1.11"]
12. Then 
14. Cat $ B | grep $ A | awk-F'' '{Print $2 }' 
16.  
18. Elif [$ A ="192.168.1.21"]
20. Then 
22. Cat $ B | grep $ A | awk-F'' '{Print $2 }' 
24.  
26. Elif [$ A ="192.168.1.31"]
28. Then 
30. Cat $ B | grep $ A | awk-F'' '{Print $2 }' 
32. Else 
34. Echo"Plase input the correct IP Address"& Exit 1
36. Fi
38. Tip: Let's see where the problem is? The script is not common.
40.  

---------- After the improvement

2. #! /Bin/bash
4. # Author oldboy
6. # QQ 1, 31333741
8. Hosts_file ="$ PWD/oldboy.txt" 
10. # Judge File
12. [! -F $ hosts_file] & Echo"No test file! "& Exit 1
14. Echo-n"Plase input IP :" 
16. ReadIP
18. # Judge IP Format
20. ["$ {# }"-Lt 8] & ["'Echo $ IP | SED's/[0-9] // g ''"! ="..."] & \
22. Echo"Plase input the correct IP Address"& Exit 1
24.  
26. # Start
28. Result1 = $ (grep"$ IP"$ Hosts_file | awk'{Print $1 }')
30. If ["$ IP"="$ Result1"]
32. Then
34. Grep"$ IP"$ Hosts_file | awk'{Print $2 }' 
36. Exit 0
38. Else 
40. Echo"Not find the hostname of $ IP" 
42. Exit 1
44. Fi
46. Tip: This method is not advisable.