Article directory
1. Awk
How Awk works:
Read text line by line, separated by space or tab key as the separator by default, save the separated fields into built-in variables, and execute editing commands according to mode or condition.
The sed command is often used to process a whole line, while awk tends to divide a line into multiple "fields" and then process it. The reading of awk information is also read line by line, and the execution result can be printed and displayed by the function of print day. In the process of using the awk command, you can use logical operators "&&"表示"与"、"| |"表示"或"、"！"表示"非"and perform simple mathematical operations
Awk command format:
awk 选项 '模式或条件 [操作]' 文件1 文件2 ...
awk -f 脚本文件 文件1 文件2 ...
Awk's common built-in variables (which can be used directly) are as follows:
| character | explain |
|---|---|
| FS | Column separator. Specifies the field separator for each line of text, defaults to spaces or tabs.与"-F"作用相同 |
| NF | Fields of the currently processed row个数 |
| NR | currently processed 行的行号(ordinal) |
| $0 | of the currently processed row整行内容 |
| $n | Fields of the currently processed 第n个row (column n) |
| FILENAME | the filename being processed |
| RS | line separator. When awk reads data from a file, it will cut the data into many records according to the definition of RS, and awk only reads one record at a time for processing. The default value is '\n' |
2. Awk output text by line
1. Output everything:
awk '{print}' shicao1.txt //输出所有内容
awk '{print $0}' shicao1.txt //输出所有内容
2. Output the contents of lines 4~6
awk 'NR==4,NR==6 {print $0}' shicao1.txt
3. Output the content of lines 4~6 (logical AND)
awk 'NR>=4&&NR<=6 {print $0}' shicao1.txt
4. Output the contents of line 4 and line 6 (logic or)
awk 'NR==4||NR==6{print}' shicao1.txt
5. Output the contents of all odd/even lines:
awk '(NR%2)==1 {print $0}' shicao1.txt //输出所有奇数行的内容
awk '(NR%2)==0 {print $0}' shicao1.txt //输出所有偶数行的内容
5. Output all even lines and display the line number
awk '(NR%2)==0 {print NR,$0}' shicao1.txt
6. Output lines starting with root
awk '/root/ {print $0}' /etc/passwd
7. Do not display the content of the tenth line
awk 'NR!=10{print $0}' shicao1.txt
8. The output ends with bash:
awk '/bash$/ {print}' /etc/passwd
9. Before processing files. The operation performed by processing the file, the END operation
awk 'BEGIN {x=0}; /nologin$/ {x++;print x,$0}; END {print x}' /etc/passwd
3. Awk outputs text by field
awk -F: '/^root/ {print $1}' /etc/passwd //output the first field in each line (separated by spaces or tabs)
awk -F: '/^root/ {print $3}' /etc/passwd //output the third field in each line (separated by spaces or tabs)
awk -F: '/^root/ {print $1,$3}' /etc/passwd //Output the contents of the first and third fields in each line
awk -F: ‘/^root/ {print $1, 3 , 3, 3 , NF}' /etc/passwd //Output the 1st, 3rd, and last field content in each line
awk -F: '$3<5 {print $0}' /etc/passwd //Output the content of the third field whose value is less than 5
awk -F: ‘$3<5 {print $3, $1}’ /etc/passwd
awk -F: '!($3>10) {print $3,$1}' /etc/passwd //Output the content of the third field whose value is less than 5
awk 'BEGIN {FS=":"};{if($3>=1000){print}}' /etc/passwd //First process the content of BEGIN, and then print the content in the text
awk -F ":" '{max=($3>=$4)?$3:$4;{print max}}' /etc/passwd //($3>$4)?$3:$4; ternary operator, if the first If the value of the 3 fields is greater than or equal to the value of the 4th field, then assign the value of the 3rd field to max, otherwise assign the value of the 4th field to max
awk -F ":" '{print NR,$0}' /etc/passwd //Output the content and line number of each line, and add 1 to the NR value after processing a record
awk -F ":" '$7~"/bash"{print $1}' /etc/passwd //Output the first field of the line separated by colons and the seventh field contains /bash
awk -F ":" '($1~"root")&&(NF==7){print $1,$2}' /etc/passwd //Output the 1st and 2nd fields of the row containing root and 7 fields in the 1st field
awk -F ":" '($7!="/bin/bash")&&($7!="/sbin/nologin"){print}' /etc/passwd //output the seventh field is neither / bin /bash, nor for all lines of /sbin/nologin
4. Call the shell command through the pipeline and double quotes
awk '{print NR}' shicao1.txt //print line number
awk ‘{print NR,$0}’ shicao1.txt
free -m | awk '/Mem:/ {print int($3/($3+$4)*100)“%”}’ // View the current memory usage percentage
awk 'BEGIN {n=0 ; while ("w" | getline) n++ ; {print n-2}}' // call the w command and use it to count the number of online users
CPU usage:
Check the current cpu usage: top | awk '{print $0}' (dynamic)
execute only once: top -b -n1
Check cpu usage:
top -b -n1 | awk '/%Cpu/ {print $8}'
top -b -n1 | awk -F, '/%Cpu/ {print $4}' | awk '{print $1}
top -b -n1 | awk -F, '/%Cpu/ {print $4}' | awk '{print 100-$1"%"}'
View the usage of the root directory:
df | awk ‘{print $5}’
df | awk ‘$NF==“/”{print $5}’
cat /proc/uptime | awk -F, '{print $1}'
date -d "$(cat /proc/uptime | awk -F. '{print $1}') second ago" //开机时长
cat shicao2.txt | sort | uniq -c //statistics
方法1：cat shicao2.txt | awk '{a[$1]++}; END{for(i in a){print i,a[i]}} ’
方法2：cat shicao2.txt | sort | uniq -c
echo “A B C D” | awk ‘BEGIN{OFS=“,”}; {print $0}’
echo “A B C D” | awk ‘BEGIN{OFS=“,”}; {$1=$1; print $0}’$1=$1 is used to activate the re-assignment of $0, that is to say, the change of the field $1... and the number of fields NF will prompt awk to recalculate the value of $0, which is usually done when $0 needs to be output after changing OFS
awk ‘BEGIN{a[0]=1; a[1]=2; a[2]=3; print a[1]}’
awk ‘BEGIN{a[0]=1; a[1]=2; a[2]=3; print a[0]}’
awk ‘BEGIN{a[0]=1; a[1]=2; a[2]=3; print a[2]}’
awk 'BEGIN{a[“abc”]=10; a[“def”]=20; a[“xyz”]=30; print a[“abc”]}
awk ‘BEGIN{a[“abc”]=10; a[“def”]=20; a[“xyz”]=30; print a[“xyz”]}’
awk ‘BEGIN{a[“abc”]=10; a[“def”]=20; a[“xyz”]=30; print a[“def”]}’
awk ‘BEGIN{a[0]=1; a[1]=2; a[2]=3; for(i in a){print i,a[i]}}’PS1: The command in BEGIN is only executed once
PS2: The subscript of the awk array can use numbers or strings, and strings need to use double quotes
5. Summary:
awk 选项 '条件 {操作}'
awk -F '分隔符' 'NR==X {print $n}'
!= > >= < <= || &&
'/字符串或正则/ {....}'
'Sn~"字符串" {...]'
!~ == != > >= < <=
awk 'BEGIN{...}; 条件{...}; END{...}'
BEGIN{
...};处理文件前的操作
条件{
...};按照条件处理文件行内突的操作
END{
...} 处理完文件所有行内容后的操作