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This article mainly introduces the relevant knowledge of "what are the special uses of AWK commands?". The editor shows you the operation process through actual cases. The operation method is simple, fast and practical. I hope this article "what are the special uses of AWK commands" can help you solve the problem.

Basic usage the awk command format is as follows: awk [- F field-separator] 'commands' input-file (s)

The [- F delimiter] is optional because awk uses spaces and tabs as the default field delimiters, so you don't need to specify this option if you want to browse for spaces between fields and the text of tabs, but if you want to browse files such as / etc/passwd, where fields are separated by colons, you must specify the-F option

Echo "this is a test" | awk'{print $0}'# # output to this is a test

Shell reads the string entered by the user and finds that |, indicates that there is a pipeline. | left or right is understood as a simple command, that is, the standard output of the previous (left) simple command points to the standard input of the next (right) standard command, awk divides the line into several fields according to the delimiter, 1 is the first field, $2 is the second sector, and so on. To print one or all fields, use the print command. This is an awk action

Echo "this is a test" | awk'{print $1}'# # output as this echo "this is a test" | awk'{print $1, $2}'# # output as this is

The contents of the / etc/passwd file are as follows

Root:x:0:0:root:/root:/bin/bash bin:x:1:1:bin:/bin:/sbin/nologin daemon:x:2:2:daemon:/sbin:/sbin/nologin adm:x:3:4:adm:/var/adm:/sbin/nologin lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin instance 1. Only show / etc/passwd account awk-F:'{print $1}'/ etc/passwd # # output as root bin daemon adm lp

2. Display the first and seventh columns of / etc/passwd, separated by commas, add the column name start1,start7 before all rows start, and add the last row, end1 End7awk-F': 'BEGIN {print "start1,start7"} {print $1 "," $7} END {print "end1,end7"}' / etc/passwd # # output as start1,start7 root,/bin/bash bin,/sbin/nologin daemon,/sbin/nologin adm,/sbin/nologin lp,/sbin/nologin end1,end7

BEGIN statements are executed before all text processing actions are executed, and END is executed after all text processing actions are executed

3. Statistics / etc/passwd file, the line number of each line and the number of columns per line The corresponding full line content awk-F:'{print NR "" NF "" $0}'/ etc/passwd # # is output as 1 7 root:x:0:0:root:/root:/bin/bash 2 7 bin:x:1:1:bin:/bin:/sbin/nologin 3 7 daemon:x:2:2:daemon:/sbin:/sbin/nologin 4 7 adm:x:3:4:adm:/var/ Adm:/sbin/nologin 5 7 lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin1 、 Support for built-in variables

In the above example, NR and NF are actually built-in variables for awk. Some of the built-in variables are as follows

Variable name explains the file name of FILENAMEawk browsing FS sets the input field separator, which is equivalent to the command line-F option NF browsing record number of fields NR read records 2, support function

The length of the output string

Awk 'BEGIN {print length ("this is a text")}'

# # change the user name of / etc/passwd to uppercase output when output is 14

Awk-F':'{print toupper ($1)}'/ etc/passwd

# # output as

ROOT BIN DAEMON ADM LP

The common functions are as follows

Function name function toupper (s) returns s uppercase tolower (s) returns s lowercase length (s) returns s length substr (sforce p) returns the suffix part of the string s starting from p, supports conditional operations, and regular expression matching

Show lines with daemon in / etc/passwd

Awk-F':'$0 ~ / daemon/' / etc/passwd # # output as

Daemon:x:2:2:daemon:/sbin:/sbin/nologinawk conditional operator describes if while do/while for break continue

Output the line where the first character of the first field is greater than d

Awk-F':'{if ($1 > "d") {print $1} else {print "-"}'/ etc/passwd

# # output as

Root-daemon-lp

You can put the flow control statement into a script, and then call the script for execution, such as the content of test.sh

{if ($1 > "d") {print $1} else {print "-"}}

Execute in the following way, and the effect is the same

Awk-F':'- f test.sh / etc/passwd

# # output as

Root-daemon-lp application scenario

The editor seldom uses awk for text analysis, and is mainly used to write scripts such as a weibo-interface-1.0.jar application. The startup script is as follows

Start.shnohup java-jar weibo-interface-1.0.jar > out 2 > & 1 &

The shutdown script is as follows, kill.sh

Kill-9 `jps-l | grep 'weibo-interface-1.0.jar' | awk' {print $1}'`

The output of jps-l is as follows

70208 com.st.kmp.main.KmpService 31036 com.st.cis.main.BaiduAnalysisService 66813 weibo-interface-1.0.jar

Also, close all the DataNode nodes of the hadoop cluster (those who don't know the hadoop can be considered as a cluster application), if each machine jps, check the pid,kill. It is troublesome to write a script directly, ssh to each node in turn, and then execute the following command

Kill `jps | grep 'DataNode' | awk' {print $1}'`

The output of jps is

508 DataNode 31481 JournalNode 31973 NodeManager about "what are the special uses of the AWK command"? thank you for your reading. If you want to know more about the industry, you can follow the industry information channel. The editor will update different knowledge points for you every day.

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