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This article will explain in detail what are the basics of Linux system shell scripts, the quality of the article content is high, so Xiaobian shares it for everyone to make a reference, I hope you have a certain understanding of relevant knowledge after reading this article.

Shell scripts also act like interpreters on Linux systems, but they are usually used to invoke external compiled programs. It then captures the output, exit code, and processes as appropriate.

Basics of Linux shell scripting

\1. Linux Scripting Basics

1.1 Introduction to grammar

1.1.1 Beginning

The program must begin with the following line (it must be on the first line of the file):

#!/ bin/sh

Symbol #! Used to tell the system that the parameters following it are the programs used to execute the file. In this example we use/bin/sh to execute the program.

When you edit a script, you must also make it executable if you want to execute it.

To make a script executable:

Compile chmod +x filename so you can use./ filename to run

1.1.2 Notes

In shell programming, comments are expressed in sentences beginning with #until the end of the line. We sincerely recommend that you use comments in your programs.

If you use comments, you can see what the script does in a short time even if you haven't used it for a long time

And how it works.

1.1.3 Variables

In other programming languages you must use variables. In shell programming, all variables consist of strings, and you don't need to specify variables.

Make a statement. To assign a variable, you can write:

#!/ bin/sh

#Assign values to variables:

a="hello world"

#Now print the contents of variable a:

echo "A is:"

echo $a

Sometimes variable names are easily confused with other words, such as:

num=2

echo "this is the $numnd"

Instead of printing "this is the 2nd," it just prints "this is the," because the shell searches for the value of the variable numnd,

But this variable has no value. You can use curly braces to tell the shell that we are printing num variables:

num=2

echo "this is the ${num}nd"

This is the 2nd.

1.1.4 Environmental variables

Variables that are processed by the export keyword are called environment variables. We don't discuss environment variables, because it's usually just a matter of logging in

Use environment variables in scripts.

1.1.5 Shell commands and flow control

There are three types of commands available in shell scripts:

1)Unix commands:

Although any unix command can be used in shell scripts, there are some relatively common commands. These commands are usually used

File and text manipulation.

Common command syntax and function

echo "some text": Print text on screen

ls: file list

wc-l filewc -w filewc -c file: Count the number of lines in a file Count the number of words in a file Count the number of characters in a file

cp sourcefile destfile: file copy

mv oldname newname : rename or move files

rm file: Delete file

grep 'pattern' file: Search for strings in a file e.g. grep 'searchstring' file.txt

cut -b colnum file: Specifies the range of file contents to be displayed and outputs them to standard output devices such as: Output

The fifth to ninth characters of each line, cut-b5 -9 file.txt, must not be confused with the cat command,

These are two completely different orders.

cat file.txt: Output file contents to standard output device (screen)

file somefile: Get file type

var read: prompts user for input and assigns input to variables

sort file.txt: Sort lines in a file.txt file

uniq: Delete rows and columns appearing in text files such as sort file.txt| uniq

expr: perform mathematical operations Example: add 2 and 3expr 2 "+" 3

find: search for files e.g. search by file name find . -name filename -print

tee: outputs data to standard output devices (screens) and files such as somecommand| tee outfile

basename file: Returns a file name without a path e.g. basename /bin/tux returns tux

dirname file: Returns the path where the file is located e.g. dirname /bin/tux will return/bin

head file: Print the first few lines of a text file

tail file : Print the last few lines of a text file

sed: Sed is a basic finder and replacement program. You can read in text from standard input, such as a command pipeline, and put

The result is output to the standard output (screen). This command searches using regular expressions (see Reference).

Don't confuse this with wildcards in shell. For example, replace linuxfocus with

LinuxFocus ：cat text.file | sed ‘s/linuxfocus/LinuxFocus/’ > newtext.file

awk: awk is used to extract fields from text files. By default, field separators are spaces, and other separators can be specified using-F.

cat file.txt |awk -F,'{print 3 }' here we use, as a field delimiter, and print at the same time

The first and third fields. Adam Bor, 34, IndiaKerry Miller, 22, USA

Adam Bor, IndiaKerry Miller, USA

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