Linux string interception and processing commands (cut, printf, awk, sed, sort, wc) notes

Linux string interception and processing commands (cut, printf, awk, sed, sort, wc) Notes

1.cut command

cut [options] filename

-f  列号　　#提取第几列（分隔符默认为\t）
-d  分隔符　　#指定分隔符

For example: cut -f 2 a.txt #Intercept the second column of the content of the file a.txt (column number starts from 1)
　　　cut -f 2,4 a.txt #Intercept the second and fourth columns of the content of the file a.txt Column
　　　cut -d ":" -f 1,3 /etc/passwd #Intercept the first column and the third column of the passwd file to: divide the first and third column

2. printf command

printf'output type output format' output content
output type:

%ns　　输出字符串，n是数字，指代输出几个字符
%ni　　输出整数。n是数字，指代输出几个数字
%m.nf　　位数和小数位数。例如：%8.2f 代表输出8位数，其中2位是小数，6位是整数
输出格式：
\a　　输出警告声音
\b　　输出退格键，也就是BackSpace键
\f　　消除屏幕
\n　　换行
\r　　回撤
\t　　水平制表符
\v　　垂直制表符

For example:
printf'%s %s %s\n' 1 2 3 4 5 6 # means every three digits are output in a group, and a newline character is added
printf'%s\t%s\t%s\t' $( cat a.txt) # means output in 4 columns

3. The awk command

awk.'Condition 1{Action 1}Condition 2{Action 2}...' File name
awk'{printf $2 “\t” $6 “\n”}' a.txt #The second column and the first column of the output file a.txt 6 columns

4. sed command

sed [options]'[action]' filename# Description: Action must be enclosed in quotation marks
Options:

-n　　一般sed命令会把所有数据都输出到屏幕。如果加入此选择，则只会把经过sed命令处理的行输出到屏幕。
-e　　允许对输入数据应用多条sed命令编辑
-i　　用sed的修改结果直接修改读取的数据的文件，而不是修改屏幕输出
动作：
a\　　追加，在当前行后添加一行或多行。添加多行时除最后一行外，每行末尾需要用"\"代表数据未完结。
c\　　行替换，用c后面的字符替换原数据行，替换多行时除最后一行外，每行末尾需要用"\"代表数据未完结。
i\　　插入，在当前插入一行或多行，插入多行时，除最后一行外每行末尾需用"\"代表数据未完结。
d　　删除，删除指定的行
p　　打印，输出指定的行
s　　字符串替换，用一个字符串替换另外一个字符串。格式为"行范围 s/旧字符串/新字符串/g"
sed可以接收管道符的输出结果

For example:

sed '2p' a.txt　　#输出第2行后，又把所有内容输出一遍
sed -n '2p' a.txt　　#只输出第二行
 
sed '2,4d' a.txt　　#删除第2到4行，只删除屏幕输出，不会更改文件本身的内容
sed '2a hello' a.txt　　#在第二行插入一行 hello
sed '2i hello' \
　　word' a.txt　　#在第二行前插入多行 hello 一行 word一行
sed '2c no person' a.txt　　#用no person 替换第二行
sed '4s/99/55/g' a.txt　　#把第4行的99替换为55
sed -i '4s/99/55/g' a.txt　　#把第4行的99替换为55,修改的是原文件而不是屏幕输出
sed -i 's/99/55/g' a.txt　　#s前不加行号时表示替换整个文件中匹配的字符串
sed -e 's/Liming//g;s/Gao//g' a.txt　　#-e表示允许多个条件执行，把Liming替换为空，把Gao替换为空

5. The sort command

sort [option] file name#sort
option:

-f　　忽略大小写
-n　　以数值型进行排序，默认使用字符串型排序
-r　　反向排序
-t　　指定分隔符，默认分隔符是制表符
-k n[,m]　　按照指定的字段范围排序。从第n字段开始，m字段结束（默认到行尾）

6. wc command

wc [options] file name#statistics
options:

-l　　只统计行数
-w　　只统计单词数
-m　　只统计字符数

7. Linux string interception command

Suppose there is a variable var=http://www.google.com/test.htm
1. # interception, delete the left character, and keep the right character.
echo ${var# //}
where var is the name of the variable, # is the operator, // means to delete the first // number and all the characters on the left from the left,
ie delete http://, the
result is: www.google .com/test.htm

2. ## is intercepted, the left character is deleted, and the right character is retained.
echo ${var## /}
## / means to delete the last (far right) / sign and all the characters on the left from the left,
ie delete http://www.google.com/ and the
result is test.htm

3. The% sign is intercepted, the characters on the right are deleted, and the characters on the left are retained.
echo ${var%/ }
%/ means that starting from the right, delete the first / sign and the characters on the right. The
result is: http://www.google.com

4. Intercept the %% sign, delete the right character, keep the left character
echo ${var%%/ }
%%/ means start from the right, delete the last (leftmost) / sign and the right character The
result is: http:

5. Starting from the first character on the left, and the number of characters
echo ${var:0:5},
where 0 means starting from the first character on the left, and 5 means the total number of characters.
The result is: http:

6. Start with the first few characters from the left and continue to the end.
The 7 in echo ${var:7}
means that the 8th character from the left starts and continues to the end.
The result is: www.google.com/test.htm

7. Starting from the first few characters from the right, and the number of characters
echo ${var:0-7:3}
where 0-7 means the seventh character from the right, and 3 means the number of characters.
The result is: test

8. Start with the first few characters from the right and continue to the end.
echo ${var:0-7}
means starting from the seventh character from the right and continuing to the end.
The result is: test.htm
Note: (The first character on the left is represented by 0, and the first character on the right is represented by 0-1)