10 Linux commands programmers need to know

As a programmer, you will use the Linux system more or less in your software development career, and you may use Linux commands to retrieve the required information. This article will share 10 useful Linux commands for developers. I hope it will be helpful to you.

The following are the Linux commands we will introduce today:

man touch, cat and less sort and grep cut sed tar find diff uniq chmod

Let us introduce them in detail one by one.

1.man command

The first Linux command you need to know is the man command, which can display the usage and description of the specified command. For example, if you want to know the usage and options of the ls command, you can execute "man ls" in the terminal:

Syntax: man man ls

~# man ls LS(1) User Commands LS(1) NAME ls - list directory contents SYNOPSIS 
ls [OPTION]... [FILE]... DESCRIPTION List information about the FILEs (the curren
t directory by default). Sort entries alphabetically if none of -cftuvSUX nor --sort is speciâ fied. Mandatory arguments to long options are mandatory for short op
tions too. -a, --all do not ignore entries starting with .

2. touch, cat and less commands

The touch command can create any type of file with a size of 0 in a Linux system. As a program developer, when you need to create a file on a Linux server, you can use the touch command:

Syntax: touch touch demo.txt

~# touch demo.txt root@devopscube:~# ls demo.txt

The cat command is used to view the contents of the file, but the cat command cannot edit the contents of the file. It can only browse the file contents. The cat command does not support the up and down keys on the keyboard to turn pages.

Syntax: cat cat demo.txt

The same less command also allows you to browse files. The less command is very fast and supports the up and down keys to view the beginning and end of the file. However, the more command is similar to it, except that the more command can only use the enter key to page forward the file, and does not support going back.

Grammar: less more

less demo.txt more demo.txt

3, sort and grep commands

The sort command is used to sort file contents. Create a file named test.txt and copy the following content into the file:

1 mike level intermediate jan 10 lucy level beginer mar 45 Dave level expert
 dec 4 dennis start beginner jul 7 Megan employee trainee feb 58 Mathew Head CEO nov

In the above example, the second column is the name, so if you want to sort the name column alphabetically, you can use the "-k" option and mark the column number, such as "-k2":

Syntax: sort sort -k2 test.txt

Sort results

~# sort -k2 test.txt 45 Dave level expert dec 4 dennis start beginner jul 10 lucy l
evel beginer mar 58 Mathew Head CEO nov 7 Megan employee trainee feb 1 mike level in
termediate jan

The first column is numbers. If you want to sort by numbers, you can use the "-h" option. If the numbers are on different columns, you can use the "-k" option after the "-h" option:

~# sort -h test.txt 1 mike level intermediate jan 4 dennis start beginner jul 7 Megan employ
ee trainee feb 10 lucy level beginer mar 45 Dave level expert dec 58 Mathew Head CEO nov

The last column is the month, you can use the "-M" option to sort the file contents by month:

~# sort -k5 -M test.txt 1 mike level intermediate jan 7 Megan employee trainee feb 10 l
ucy level beginer mar 4 dennis start beginner jul 58 Mathew Head CEO nov 45 Dave level e
xpert dec

Note: If you want to eliminate duplicate lines, you can use the "-u" option after the sort command.

Use the "-r" option to sort the files in reverse order:

~# sort -h -r test.txt 58 Mathew Head CEO nov 45 Dave level expert dec 10 lucy level beginer mar
 7 Megan employee trainee feb 4 dennis start beginner jul 1 mike level intermediate jan

Grep command:

The Grep command is very powerful and is often used by system administrators. The grep command can search for a string in a specified format in a file and output it to standard.

Syntax: grep “” grep “Mathew” test.txt

~# grep "dennis" test.txt 4 dennis start beginner jul

The output of the above command contains this substring. If you want to retrieve the complete word, you need to add the "-i" option. At the same time, you can also use the grep command to search for strings in multiple files. The command code is as follows:

while(!game_over) { for each possible move: count_no_of_merges_for_2-tiles and 4-tiles choose the move with large number of merges }
grep "dennis" test1.txt test2.txt test3.txt

Of course you can also use regular expressions to match strings.

4. cut command

cut command allows you to extract specified parts of a file using columns or delimiters. If you want to list the entire contents of a column in the file, you can use the "-c" option. For example, the following will extract the entire contents of columns 1 and 2 from the test.txt file.

cut -c1-2 test.txt
~# cut -c1-2 test.txt 1 10 45 4 7 58

If you wish to extract a specified string from the file, then you can use the delimiter options "-d" and "-f" options to select the columns. For example, we can use the cut command to extract the names column:

cut -d' ' -f2 test.txt
~# cut -d' ' -f2 test.txt mike lucy Dave dennis Megan Mathew

The following example extracts the users column from the /etc/passd file:

cut -d':' -f1 /etc/passwd

5. sed command

sed is an online editor that processes content one line at a time. During processing, the currently processed line is stored in a temporary buffer, called "pattern space", and then the sed command is used to process the contents of the buffer. After the processing is completed, the contents of the buffer are sent to the screen. Then process the next line, and repeat until the end of the file. The file contents are not changed unless you use redirection to store the output.

If you want to search and replace specific content in a file, you can use the "s" option to retrieve it and replace it.

Syntax: sed ‘s///’ test.txt

For example, replace "mike" with "michael" in the test.txt file:

sed 's/mike/michael/' test.txt
~# sed 's/mike/michael/' test.txt 1 michael level intermediate jan 10 lucy
 level beginer mar 45 Dave level expert dec 4 dennis start beginner jul 7 Megan employee 
trainee feb 58 Mathew Head CEO nov

6. tar command

The tar command is used to compress and decompress files, in which the "-cf" and "-xf" options are often used.

Syntax: tar

Let’s package the test.txt file:

tar -cf test.tar test.txt
~# tar -cf test.tar test.txt root@devopscube:~# ls test.tar test.txt

Use the "-C" option to decompress the test.tar file just packaged to the "demo" directory:

tar -xf test.tar -C /root/demo/
~# tar -xf test.tar -C /root/demo/ root@devopscube:~# cd demo/ root@devopscube:~/demo# ls test.txt

7. find command

The find command is used to retrieve files. You can use the "-name" option to retrieve files with a specified name:

find -name find -name test.txt
~#/home/ubuntu# cd ~ root@devopscube:~# find -name test.txt ./demo/test.txt ./test.txt

You can also use "/ -name" to retrieve the folder with the specified name:

find / -name passwd
~# find / -name passwd /etc/cron.daily/passwd /etc/pam.d/passwd /etc/passwd /usr/share/lintian/o
verrides/passwd

8. diff command

The diff command is used to find the differences between two files. The diff command analyzes the file content and then prints out different lines. The following example can find the differences between the two files test and test1

Syntax: diff diff test.txt test1.txt

~# diff test.txt test1.txt 7c7  59 sdfsd CTO dec

9、Uniq命令

uniq命令用来过滤文件中的重复行：

语法: uniq uniq test.txt

~# uniq test.txt 1 mike level intermediate jan 10 lucy level beginer mar 45 Da
ve level expert dec 4 dennis start beginner jul 7 Megan employee trainee feb 58 Mathew 
Head CEO nov

10、chmod命令

chmod命令用来改变文件的读/写/执行权限，权限数值如下所示：

4 – read permission 2 – write permission 1 – execute permission 0 – no permission

下面的命令可以给test.txt文件赋最高的权限：

chmod 755 test.txt

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