Linux Series-shell Learning notes

First record

1, the simple HelloWorld writing

Input command under Shell input:VI helloworld.sh

Then enter the text editor:

#!/bin/shell#this is Ahelloworld testa= "HelloWorld" echo $a

Execute helloworld.sh File

Command:

# sh helloworld.sh

2, the variable assignment method is

# variable_name = Variable_value

If you assign a value to a variable that already has a value, the new value supersedes the old value. To take a value in front of the variable name plus $, $variable _name can be used in quotation marks, if there is confusion, you can use curly braces to distinguish, for example:

# echo "Hi, $as"

Will not output "Hi, helloworlds", but output "Hi,". This is because the shell treats $as as a variable, and $as is not assigned a value, and its value is empty. The correct method is:

$ echo "Hi, ${a}s"

Variables in single quotes do not perform variable substitution operations.

3.who command to see who has logged in to the system

who| Wc–l Computing total number of users

4.cat > Nusers Creating File Nusers, using cat copy terminal input

echo "haha"

Then ctrl+d represents the end of the file

Use chmod +x nesers to let the file have permission to execute

Test:./nusers

Shell recognizes three types of commands: Built-in commands, shell functions, and external commands

The difference between 5.printf and Echo

printf does not have the ability to wrap lines like echo

6. Redirection and piping

7.shell command

# who see who's logged in # Date view current date # chmod +x file to modify file to make it executable # echo Display text string Contents # Cat file shows the contents of the file, and more almost #./file Execute File # s ET shows the complete environment variable configuration list # testing= ' Date ' action: output value; The date value is output and assigned to testing# $testing $ for the value of the output variable # command > OutputFile writes the results of command commands to the outputfile file (overwrite write) # command >> OutputFile writes the results of command commands to the OutputFile file (append write) # The WC << EOF prompt always prompts for input data, knows the input EOF, and then the WC command begins the inline input redirection provided by the Data execution line, Word, and byte count. # RPM–QA > Rpm.list to enter the installed package list data into rpm.list# sort rpm.list sorting rpm.list# Rpm–qa | Sort by pipe | Add two commands to a # expr 1 + 5expr to perform the addition operation, resulting in a floating-point arithmetic command # $6#BC? View exit status code for the last command

Second note

1.for command

Format:

for Var in listdocommandsdone

Write a program that iterates through the list, as follows:

[[Email protected] test]# VI sh1201#!/bin/shfor i in liudiwei haha xiaoli liangliang xuxudo        echo ' This is my friend $i "Done

Test

[Email protected] test]#./sh1201this is my friend liudiweithis are my friend Hahathis is my friend Xiaolithis is my Frien D liangliangthis is my friend Xuxu

If the list contains single quotes, such as I ' m a student.

There are two ways to fix it:

(1) using the escape character I\ ' m a student

(2) Use double quotation marks to define the value used in single quotation marks. "I ' m" a student.

2.while command

The format of the while command:

While Test Commanddo other Commandsdone

Writing Testwhile

[Email protected] test]# VI testwhile#!/bin/shi=0while [$i-le]do        echo "i= $i"        i=$[$i + 1]done

Test:

[Email protected] test]#./testwhilei=0i=1i=2i=3i=4i=5i=6i=7i=8i=9i=10

3.util command

Command format

Until Test commandsdo other Commandsdone

Note: Until commands is true, the other commands is always executed.

4. Nested loop output 99 multiplication table

Edit a new file

[Email protected] test]# VI mutil99

99 Multiplication Table Code:

#/bin/shfor ((i=1;i<=9;i++)) do for        ((j=1;j<=i;j++))        do                echo-n "$j * $i =$[$i * $j]"        done Echodone

Results:

[Email protected] test]#/mutil991*1=11*2=2 2*2=41*3=3 2*3=6 3*3=91*4=4 2*4=8 3*4=12 4*4=161*5=5 2*5=10 3*5=15 4*5=20 5* 5=251*6=6 2*6=12 3*6=18 4*6=24 5*6=30 6*6=361*7=7 2*7=14 3*7=21 4*7=28 5*7=35 6*7=42 7*7=491*8=8 2*8=16 3*8=24 4*8=32 5*8= 40 6*8=48 7*8=56 8*8=641*9=9 2*9=18 3*9=27 4*9=36 5*9=45 6*9=54 7*9=63 8*9=72 9*9=81

5.break and Continue

6. Processing the loop output

Iterate through the folder and determine whether it is a directory or a file

[Email protected] test]# vi isdirorfile#/bin/shfor file In/root/*do        if [-D "$file] then                echo" $file is a directory! "        else                echo "$file is a file!"        Fidone    > Output.txt  #讲结果输出到output. txt file

Results

[Email protected] test]# More output.txt/root/anaconda-ks.cfg are a file!/root/dead.letter is a file!/root/downloads is a Directory!/root/hadoop is a directory!/root/hello.sh is a file!/root/initial-setup-ks.cfg are a file!/root/src is a directo Ry!/root/test is a DIRECTORY!/ROOT/TESTQ is a file!

Linux Series-shell Learning notes