AWK introduction and use

1, Introduction to awk

awk is a programming language used to process text and data under linux/unix.

The data can come from standard input, one or more files, or the output of other commands.

It supports advanced functions such as user-defined functions and dynamic regular expressions. It is linux/unix
A powerful programming tool under.

It is used on the command line, but it is more used as a script.

awk processes text and data in such a way that it scans the file line by line, from the first line to the last line, looks for lines matching a specific pattern, and performs the operation you want on these lines. If no processing action is specified, the matching lines are displayed to the standard output (screen). If no mode is specified, all the lines specified by the operation are processed.

awk stands for the first letter of the author's last name. Because it is written by three people, Alfred Aho, Brian Kernighan and Peter Weinberger.

gawk is the GNU version of awk, which provides some extensions of Bell Labs and GNU.

2, Two formal syntax formats of awk

awk [options] 'commands' file1 file2

awk [options] -f awk-script-file filenames

options:

-F for the content processed each time, you can specify a sub defined separator. The default separator is a blank character (space or tab key)

command:

BEGIN{}                        {}               END{}

Action before processing all content       Actions in processing content actions after processing all content

Examples

 awk 'BEGIN{print "----Start processing---"} {print "ok"} END{print "----All processed---"}' /etc/hosts
----Start processing---
ok
ok
ok
----All processed---

BEGIN {} is usually used to define some variables, such as BEGIN{FS=":";OFS = "---"}

3, awk working principle

[root@5e4b448b73e5 ~]# awk -F:  '{print $1,$3}' /etc/passwd
root 0
bin 1
daemon 2
adm 3
...slightly...

(1)awk will process each line of the file. Each time, it uses one line as input and assigns this line to the internal variable $0. Each line can also be called a record and ends with a newline character

(2) Then, the line is** 😗* (space or tab by default) is broken down into fields (or fields), and each field is stored in a numbered variable, starting with $1,
Up to 100 fields

(3) How does awk know how to separate fields with white space characters? Because there is an internal variable fs to determine the field separator. Initially, FS is assigned as a blank character

(4) When awk prints fields, it will print with the built-in method using the print function. Awk adds a space between the printed fields. This space is an internal variable. The separator and comma of OFS output field will be mapped with OFS. The value of this output separator can be controlled through OFS.

(5) After awk output, another line will be obtained from the file and stored in $0, overwriting the original content, and then the new string will be separated into fields and processed. This process will continue until all rows are processed

4, Record internal variables related to fields:

View help:

man awk

$0: the awk variable $0 holds the contents of the line currently being processed
NR: the line currently being processed is awk the total number of lines processed.
FNR: the line number of the line currently being processed in its file.
NF: the total number of fields when each row is processed
$NF: the value of the last field after the separation of the current processing line
FS: field separator when entering a line. The default is blank character (space tab)

OFS: output field separator, which is a space by default

awk 'BEGIN{FS=":"; OFS="+++"} /^root/{print $1,$2,$3,$4}' /etc/passwd

ORS output record separator. The default is newline

Examples

Merge each line of the file into one line

ORS outputs a record by default and should enter, but a space is added here

awk 'BEGIN{ORS="  "} {print $0}' /etc/passwd

Output:

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  sync:x:5:0:sync:/sbin:/bin/sync  shutdown:x:6:0:shutdown:/sbin:/sbin/shutdown  halt:x:7:0:halt:/sbin:/sbin/halt  mail:x:8:12:mail:/var/spool/mail:/sbin/nologin  operator:x:11:0:operator:/root:/sbin/nologin  games:x:12:100:games:/usr/games:/sbin/nologin  ftp:x:14:50:FTP User:/var/ftp:/sbin/nologin  nobody:x:99:99:Nobody:/:/sbin/nologin  systemd-network:x:192:192:systemd Network Management:/:/sbin/nologin  dbus:x:81:81:System message bus:/:/sbin/nologin  tss:x:59:59:Account used by the trousers package to sandbox the tcsd daemon:/dev/null:/sbin/nologin  [root@5e4b448b73e5 ~]#

5, Format output:

printf function

awk -F: '{printf "%-15s %-10s %-15s\n", $1,$2,$3}' /etc/passwd
awk -F: '{printf "|%-15s| %-10s| %-15s|\n", $1,$2,$3}' /etc/passwd

%s character type
%d decimal integer
%f floating point type, with 2 digits after the decimal point reserved. printf "%.2f\n" 10
%-15s takes up 15 characters - indicates left alignment, and the default is right alignment
printf will not automatically wrap at the end of the line by default, plus \ n

6, awk mode and action

Any awk statement consists of patterns and actions.

The mode section determines when an action statement is triggered.
If the mode part is omitted, the action in the command will act on each line.

The mode can be

regular expression
Logical expression
Compound statement containing regular expression and logical expression

1 regular expression:

Regular matching the whole row (including):

Is whether the currently processed row contains the specified pattern (written regular expression)
/Regular / regular needs to be written in double slash

! Used for negation, which is to find rows that do not match the regular pattern

The default action of AWK is to print the whole line, so when printing the whole line, the action command of printing can be omitted.

awk '/^root/' /etc/passwd
awk '!/^root/' /tec/ passwd

Regular match a field:

Matching operators that can be used (~ and! ~)
Field ~ / regular/

awk -F: '$3 ~ /^1/' /etc/passwd
awk -F: '$NF !~ /bash$/' /etc/passwd

Match lines that start with bin or start with root

awk -F: '/^(bin|root)/' /etc/passwd
# output
root:x:0:0:root:/root:/bin/zsh
bin:x:1:1:bin:/bin:/sbin/nologin

2 logical expression

The logical expression uses to compare the text. The specified action is executed only when the condition is true.
Logical expressions use * * * relational operator * * * to compare two values, which can be used to compare numbers with strings.

To achieve the exact equality of strings, you need to use = = and=

The string needs to be enclosed in double quotation marks

awk -F: '$NF == "/bin/bash"' /etc/passwd
awk -F: '$1 == "root"' /etc/passwd

Other operation symbols:

Relational operators have
< less than, e.g. x < y
>Greater than, for example, x > y
< = less than or equal to, e.g. x < = y
==Equal to e.g. x==y
!= Not equal to, for example, X= y
>=Greater than or equal to, e.g. x > = y`

Examples

awk -F: '$3 == 0' /etc/passwd
awk -F: '$3 < 10' /etc/passwd

df -P | grep '/' |awk '$4 > 25000 {print $0}'

Arithmetic operations: +, -, *, /,% (modulus: remainder), ^ (Power: 2 ^ 3)

You can perform calculations in logical expressions, and awk will perform arithmetic operations as floating-point numbers

awk -F: '$3 * 10 > 5000{print $0}' /etc/passwd

Compound mode 3

In coincidence mode, logical operation symbols are usually used

&&Logical and, equivalent to and
||Logical or, equivalent to or
! Logical negation

awk -F: '$1~/root/ && $3<=15' /etc/passwd
awk -F: '$1~/root/ || $3<=15' /etc/passwd
awk -F: '!($1~/root/ || $3<=15)' /etc/passwd

4 range mode

The patterns are separated by commas

The syntax used is: start expression and end expression

The following meaning is: from the beginning of the line with bin to the end of the line with adm
That is, all contents from the line beginning with bin to the line containing adm meet the matching conditions.

awk -F: '/^bin/,/adm/ {print $0 }' /etc/passwd
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

The range mode is not combined with other modes

The following d operation is invalid

[root@shark ~]# echo Yes | awk '/1/,/2/ || /Yes/'
[root@shark ~]#

Comprehensive practice

Organization No. organization name        Province    Trunk No. trunk status receiving teller No. receiving teller name    currency    balance
11007eee        Beijing Dongcheng District Street sub branch    03      Unclaimed           one hundred and fifty-six     nineteen thousand and one.68
11007fff        Beijing Dongcheng District Street sub branch    03      Unclaimed           eight hundred and forty     two thousand six hundred and seventy-two.00
11007aaa        Beijing Dongcheng District Street sub branch    04      Unclaimed           one hundred and fifty-six     seven thousand two hundred and sixty-one.31
11007ccc        Beijing Chaoyang District Road sub branch    02      Unclaimed           one hundred and fifty-six     one hundred and sixty-one thousand four hundred and ninety.08
110088ee        Beijing Chaoyang District Road sub branch    03      Unclaimed           eight hundred and forty     nineteen thousand seven hundred and eleven.00
34009eff         Shanxi Coal Mine Road sub branch    03      Unclaimed           one hundred and fifty-six     two hundred and eighty-two thousand three hundred and seventy.23
11007eee        Shanxi colliery District Road sub branch    03      Unclaimed           one hundred and fifty-six     two hundred and eighty-two thousand three hundred and seventy.23
11007eee        Shanxi colliery District Road sub branch    03      Unclaimed           one hundred and fifty-six     two hundred and eighty-two thousand three hundred and seventy.23
11007264        Shandong Pingyin County sub branch     Shandong    02      Unclaimed          one hundred and fifty-six     three hundred and four thousand five hundred and sixteen.23
11007889        Shandong Jiyang County sub branch Beijing    04      Unclaimed           eight hundred and forty     twenty-four thousand five hundred and fifty-one.00
11007264        Beijing Chaoyang District sub branch     Beijing    02      Unclaimed           one hundred and fifty-six     three hundred and four thousand five hundred and sixteen.23
11007284        Beijing Chaoyang District sub branch     Beijing    02      Requisition     1002 Lich King           one hundred and fifty-six     three hundred and four thousand five hundred and sixteen.23
11007194        Beijing Chaoyang District Bank       Beijing    02      Unclaimed           one hundred and fifty-six     three hundred and four thousand five hundred and sixteen.23
11007264        Henan Zhongyuan District sub branch     Henan    02      Unclaimed          one hundred and fifty-six     three hundred and four thousand five hundred and sixteen.23
11007284        Henan Erqi sub branch     Henan    03      Requisition     1003 Zhong Kui     one hundred and fifty-six     nine thousand and forty-six.23

Find the unclaimed, organization number and balance of the trunk in Henan Province#
Find all the structure numbers in Beijing,
Find the organization in Beijing and the trunk is not collected
Find county-level sub branch#
Find Pingyin County sub branch
Find Beijing branch with balance greater than 8000#
Find out which tellers have used the trunk, and print out the teller number and teller name
All require formatted output#

7, awk scripting

1 if statement

Format {if (expression) {statement; statement;...}}

awk -F: '{ if ($3==0) {print $1 " is administrator."}}' /etc/passwd
 Output: root is administrator.

# Count the number of system level users
awk -F: '{ if ($3>0 && $3<1000) {count++}  } END{print count}' /etc/passwd 
Output: 22

2. If... else statement

Format {if (expression) {statement; statement;...} else {statement; statement;...}}

awk -F: '{ if ($3==0){print $1} else {print $7} }' /etc/passwd

awk -F: '{ if ($3==0){count++} else{i++} } END{print "Number of administrators: "count "Number of system users: "i}' /etc/passwd
 Input:
Number of administrators: 1 Number of system users: 24

awk -F: '{ if($3==0){count++} else{i++} } END{print "Number of administrators: "count ; print  "Number of system users: "i}' /etc/passwd
 Output:
Number of administrators: 1
 Number of system users: 24

3 if... else if... else statement

format
{if (expression 1) {statement; statement;...} else if (expression 2) {statement; statement;...} else if (expression 3) {statement; statement;...} else {statement; statement;...}}

awk -F: '{if($3==0){i++} else if($3>999){k++} else{j++}} END{print i; print k; print j}' /etc/passwd

Output:
1
2
22

awk -F: '{if($3==0){i++} else if($3>999){k++} else{j++}} END{print "Number of administrators: "i; print "Number of ordinary: "k; print "System user: "j}' /etc/passwd

Output:
Number of administrators: 1
 Number of ordinary: 2
 System user: 22

8, awk uses external variables:

1 use custom shell variables

Method 1: awk parameter - v (recommended and easy to read)

[root@shark ~]# read -p ">>:" user
>>:root
[root@shark ~]# awk -F: -v awk_name=$user '==awk_name {print "user exists"} '/ etc/passwd
 User presence
[root@shark ~]#

2 use the environment variables of the shell

[root@shark ~]# read -p ">>:" user
>>:root
[root@shark ~]# export user
[root@shark ~]# awk -F: '==ENVIRON["user"] {print "user exists"}' / etc/passwd
 User presence
[root@shark ~]# unset user

9, Specify multiple delimiters: []

echo "a b|c d| ||||e | |" |awk -F'[ |]' '{print $10}'
e
echo "a b|c d| ||||e | |" |awk -F'[ |]+' '{print $5}'
e

[root@shark ~]# echo "110.183.58.144 - - [10/May/2018:23:49:27 +0800] GET http://app." |awk -F'[][ ]'  '{print $5 }'
10/May/2018:23:49:27
[root@shark ~]# echo "110.183.58.144 - - [10/May/2018:23:49:27 +0800] GET http://app." |awk -F'[][ ]+'  '{print $4 }'
10/May/2018:23:49:27

Note: any characters in brackets are regarded as ordinary characters, such as* Are regarded as ordinary characters.
For example:

$ echo "a.b*c" |awk -F'[.*]' '{print $1, $2,$3}'
a b c

Job:
1. Obtain network card IP (all IP except ipv6)
2. Get the memory usage
3. Get disk usage
5. Print out the last field of / etc/hosts file (separated by spaces)
6. Print the directory name under the specified directory

10, Production example:

Count and sort the IP accesses in a certain time range in the log

Partial log

110.183.58.144 - - [10/May/2018:23:49:27 +0800] "GET http://app.znds.com/html/20180504/y222sks_2.2.3_dangbei.dangbei HTTP/1.1" 200 14306614 "-" "okhttp/3.4.1"
1.69.17.127 - - [10/May/2018:23:49:31 +0800] "GET http://app.znds.com/down/20180205/ttjs_3.0.0.1_dangbei.apk HTTP/1.1" 200 13819375 "-" "okhttp/3.4.1"
1.69.17.127 - - [10/May/2018:23:49:40 +0800] "GET http://app.znds.com/down/20180416/ttyj_1.1.6.0_dangbei.apk HTTP/1.1" 200 16597231 "-" "okhttp/3.4.1"
1.69.17.127 - - [10/May/2018:23:50:00 +0800] "GET http://app.znds.com/down/20170927/jydp_1.06.00_dangbei.apk HTTP/1.1" 200 36659203 "-" "okhttp/3.4.1"

Concrete implementation

Log file name: app log

$ start_dt='10/May/2018:23:47:43
$ end_dt='10/May/2018:23:49:05'
$ awk -v st=${start_dt} -v ent=${end_dt} -F'[][ ]' '$5 == st,$5 == ent  {print $1}' app.log  |sort |uniq -c |sort -nr |head -n 10
     66 223.13.142.15
      6 110.183.13.212
      4 1.69.17.127
      1 113.25.94.69
      1 110.183.58.144

Time conversion tool

[root@shark ~]# unset months_array
[root@shark ~]# declare -A month_array
[root@shark ~]# month_array=([01]="Jan" [02]="Feb" [03]="Mar" [04]="Apr" [05]="May" [06]="Jun" [07]="Jul" [08]="Aug" [09]="Sept" [10]="Oct" [11]="Nov" [12]="Dec")
[root@shark ~]# echo ${month_array[01]}
[root@shark ~]# Jan
[root@shark ~]# m=10
[root@shark ~]# echo ${month_array[$m]}
[root@shark ~]# Oct

String slicing

Syntax: ${var: start with this index number: how many characters to take out:}

Index numbers start at 0

[root@shark ~]# st="20180510234931"
[root@shark ~]# m=${st:4:2}
[root@shark ~]# echo $m
[root@shark ~]# 05

Common log analysis statements

# TOP 20 IP access
16348 58.16.183.52
awk  '$9==200 {print $1}'  2018-05-10-0000-2330_app.log | sort |uniq -c |sort -r |head -20


# Access the IP address of TOP 10 with status code 20X
2097 125.70.184.99
2000 183.225.69.158
awk  '$9 > 200 && $9 < 300{print $1}' 2018-05-10-0000-2330_app.log  | sort |uniq -c |sort -r |head


# url to access TOP 20
250563 http://app.xxx.com/update/2018-04-04/dangbeimarket_4.0.9_162_znds.apk
awk  '$9 == 200{print $7,$9}' 2018-05-10-0000-2330_app.log | sort |uniq -c |sort -r |head -20

# Access the url of TOP 10 with status code 20X
248786 http://app.znds.com/update/2018-04-04/dangbeimarket_4.0.9_162_znds.apk
awk  '$9 > 200 && $9 < 300{print $7,$9}' 2018-05-10-0000-2330_app.log | sort |uniq -c |sort -r |head


# IP with more than 1W accesses
58.16.184.247
58.16.183.52
awk  '{print $1}' 2018-05-10-0000-2330_app.log| sort |uniq -c |sort -r |awk '$1 > 10000 {print $1}'


# Access the url of TOP 10 with status code 404
1017 http://app.xxx.com/update/fixedaddress/kuaisou_qcast.apk.md5
awk  '$9 == 404 {print $1}' 2018-05-10-0000-2330_app.log | sort |uniq -c |sort -r |head

11, Improve article

1 split information into files

awk splitting files is very simple, just use redirection.

The following example is to separate files according to the third example, which is quite simple (NR!=1 means that the header is not processed).

$ awk 'NR!=1{print > $3}' gy.txt
$ ls
gy.txt  Beijing Shanxi     Shandong Henan

You can also output the specified columns to a file:

awk 'NR!=1{print $2,$3,$4,$5 > $3}' gy.txt

A little more complicated: (note the if else if statement. It can be seen that awk is actually a script interpreter)

$ awk 'NR!=1 {if($3 ~ /Beijing|Shandong/) print > "1.txt";
else if($3 ~ /Shanxi/) print > "2.txt";
else print > "3.txt" }' gy.txt
 
$ ls ?.txt
1.txt  2.txt  3.txt

2 AWK array

Syntax: array_name[index]=value

array_name array name
Index index
Value value

The array in awk is the same as the associative array in shell. The index can be any string, and the index can also use the corresponding valid variables.

[root@shark ~]# awk 'BEGIN{
arr["a"]=1;
arr["b"]=2+3;
print arr["a"];
print arr["b"]
}'
1
5
[root@shark ~]# echo "a b" |awk 'BEGIN{
arr["a"]=1;
arr["b"]=2+3;
print arr["a"];
print arr["b"]
}'
1
5

Sample file

Void Walker mathematics 68
 Void Walker English 88
 Dark girl language 98
 Dark girl math 68
 Wuji swordsman language 78
 Wuji Jiansheng mathematics 48
 Zither fairy language 90
 Harp fairy mathematics 68
 Harp fairy English 61
 Main language of shadow stream 68
 Master of shadow flow 88
 Main English 98

[root@shark ~]# awk '{arr[$1]++;print $1,arr[$1]}' hero
 Void Walker 1
 Void Walker 2
 Daughter of darkness 1
 Daughter of darkness 2
 Limitless swordsman 1
 Limitless swordsman 2
 Harp fairy 1
 Harp fairy 2
 Harp Fairy 3
 Master of shadow stream 1
 Master of shadow flow 2
 Master of shadow flow 3

[root@shark ~]# awk '{arr[$1]++} END{print $1,arr[$1]}' hero
 Master of shadow flow 3

[root@shark ~]# awk '{arr[$1]++} END{for (i in arr) print i, arr[i]}' hero
 Daughter of darkness 2
 Void Walker 2
 Harp Fairy 3
 Master of shadow flow 3
 Limitless swordsman 2
[root@shark ~]#

Let's take another look at the usage of counting the number of outlets in each province:

$ awk 'NR!=1 {a[$3]++;} END {for (i in a) print i ", " a[i];}' gy.txt
 Beijing, 69
 Shanxi, 20
 Jiangsu, 10
 Shandong, 16

3 examples of built-in functions

#Find a line with a length greater than 80 from the file
awk 'length>80' file

# Length is the built-in function of awk, and the job is to count the string length of each line

4 casual play

The following command calculates the total file size of all txt files.

$ ls -l  *.txt | awk '{sum+=$5} END {print sum}'
2511401

other

# Let's take a look at how much memory each user's process occupies (Note: RSS column of sum)

$ ps aux | awk 'NR!=1 {a[$1]+=$6;} END { for(i in a) print i ", " a[i]"KB";}'

#View client IP by number of connections
netstat -ntu | awk '{print $5}' | cut -d: -f1 | sort | uniq -c | sort -nr
 
#Print 99 multiplication table
seq 9 | sed 'H;g' | awk -v RS='' '{for(i=1;i<=NF;i++)printf("%dx%d=%d%s", i, NR, i*NR, i==NR?"\n":"\t")}'

Sample data

110.183.58.144 - - [10/May/2018:23:49:27 +0800] "GET http://app.znds.com/html/20180504/y222sks_2.2.3_dangbei.dangbei HTTP/1.1" 200 14306614 "-" "okhttp/3.4.1"
1.69.17.124 - - [10/May/2018:23:49:31 +0800] "GET http://app.znds.com/down/20180205/ttjs_3.0.0.1_dangbei.apk HTTP/1.1" 200 13819375 "-" "okhttp/3.4.1"
1.69.17.125 - - [10/May/2018:23:49:40 +0800] "GET http://app.znds.com/down/20180416/ttyj_1.1.6.0_dangbei.apk HTTP/1.1" 200 16597231 "-" "okhttp/3.4.1"
1.69.17.126 - - [10/May/2018:23:50:00 +0800] "GET http://app.znds.com/down/20170927/jydp_1.06.00_dangbei.apk HTTP/1.1" 200 36659203 "-" "okhttp/3.4.1"
1.69.17.127 - - [10/May/2018:23:50:00 +0800] "GET http://app.znds.com/down/20170927/jydp_1.06.00_dangbei.apk HTTP/1.1" 200 36659203 "-" "okhttp/3.4.1"
1.69.17.128 - - [10/May/2018:23:50:00 +0800] "GET http://app.znds.com/down/20170927/jydp_1.06.00_dangbei.apk HTTP/1.1" 200 36659203 "-" "okhttp/3.4.1"
1.69.17.129 - - [10/May/2018:23:50:00 +0800] "GET http://app.znds.com/down/20170927/jydp_1.06.00_dangbei.apk HTTP/1.1" 200 36659203 "-" "okhttp/3.4.1"

#!/bin/bash

declare -A month_array

month_array=([01]="Jan" [02]="Feb" [03]="Mar" [04]="Apr" [05]="May" [06]="Jun" [07]="Jul" [08]="Aug" [09]="Sept" [10]="Oct" [11]="Nov" [12]="Dec")

st=$1
end=$2
logfile=$3

start_yer=${st:0:4}
start_month=${st:4:2}
start_day=${st:6:2}
start_h=${st:8:2}
start_m=${st:10:2}
start_s=${st:12:2}

# Get mapped month
start_month=${month_array[$start_month]}

# Replace the date and time entered by the user with the format in the log: 10/May/2018:23:49:31
start_dt="$start_day/$start_month/${start_yer}:${start_h}:${start_m}:$start_s"

echo $start_dt

end_yer=${end:0:4}
end_month=${end:4:2}
end_day=${end:6:2}
end_h=${end:8:2}
end_m=${end:10:2}
end_s=${end:12:2}

end_month=${month_array[$end_month]}
end_dt="$end_day/$end_month/${end_yer}:${end_h}:${end_m}:$end_s"

echo $end_dt
echo $logfile

export start_dt end_dt

awk -F '[][  ]+' '{
if ($4==ENVIRON["start_dt"]){flag=1}
else if($4==ENVIRON["end_dt"]){flag=0};
if (flag || $4==ENVIRON["end_dt"]){print $1}
}'   $logfile

unset start_dt
unset end_dt

[root@shark ~]# sh search-log.sh 20180510234931 20180510235000 access.log
10/May/2018:23:49:31
10/May/2018:23:50:00
access.log
1.69.17.124
1.69.17.125
1.69.17.126
1.69.17.127
1.69.17.128
1.69.17.129

12, References

Built in variables, see: http://www.gnu.org/software/gawk/manual/gawk.html#Built_002din-Variables

For flow control, see: http://www.gnu.org/software/gawk/manual/gawk.html#Statements

Built in functions, see: http://www.gnu.org/software/gawk/manual/gawk.html#Built_002din

Regular expressions, see: http://www.gnu.org/software/gawk/manual/gawk.html#Regexp

Keywords: Linux

Added by deadparrot on Thu, 17 Feb 2022 22:37:17 +0200

Programming VIP

AWK introduction and use

1, Introduction to awk

2, Two formal syntax formats of awk

awk [options] 'commands' file1 file2

awk [options] -f awk-script-file filenames

options:

command:

Examples

3, awk working principle

4, Record internal variables related to fields:

Examples

5, Format output:

6, awk mode and action

1 regular expression:

2 logical expression

Compound mode 3

4 range mode

Comprehensive practice

7, awk scripting

1 if statement

2. If... else statement

3 if... else if... else statement

8, awk uses external variables:

1 use custom shell variables

2 use the environment variables of the shell

9, Specify multiple delimiters: []

10, Production example:

11, Improve article

1 split information into files

2 AWK array

3 examples of built-in functions

4 casual play

12, References

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