Essential Linux Commands Every Programmer Should Know

Source: Frontend Dissuader | ID: quantuishiAuthor: Frontend Dissuader

Introduction

Programmer: “I’m out of here, be careful with the person who told me the command line is rm -rf /*.”

“rm -rf” has caused disasters among novice programmers, as those new to the field often lack a solid foundation.

It’s easy to feel helpless without a graphical user interface (GUI), leading to embarrassing situations where one doesn’t even know how to deploy an application.

I believe that mastering Vim and common commands in Linux is a compulsory course for every programmer.

Moreover, even Microsoft has embraced Linux terminal by launching Windows Terminal. What other reasons do you have not to learn?

1. grep: Find Keywords in Files

$ grep "string" [options] file

Use the grep command to find all React keywords in a file:

• The -i option allows case-insensitive searching in the file. It matches words like “REACT“, “REact“, and “react“.

  $ grep -i "REact" file

• The -c (count) option finds the number of lines matching a given string/pattern.

  $ grep -c "react" index.js

For more options, see the image below:

2. ls: List Files and Directories in Current Path

$ ls

ls lists files and directories in the current path.

• If it’s a folder, it appears in blue.
• If it’s a file, it appears in gray.

3. pwd: Display Current Working Directory

$ pwd

4. cat: View File Contents

$ cat somefile.js

The cat command primarily has three functions:

1. Display the entire file at once.

$ cat filename

1. Create a file and fill it with the output of the previous command.

$ cat > filenamebr

Can only create new files, cannot edit existing ones.

1. Combine several files into one file.

   $ cat file1 file2 > file

The following example copies index.js to index2.js

5. echo: Output a String

$ echo "some text"

This is a built-in command mainly used in Shell scripts and batch files to output status text to the screen or a file.

6. touch: Create a File

$ touch somefile

The touch command is used to create an empty file.

Note that in the image above, we used touch to create a file and cat to view its contents. Since the newly created index2.js file is empty, cat returns no output.

Here are the main differences between cat and touch:

• cat is used to create files with content.
• touch creates an empty file with no content.

7. mkdir: Create a New Empty Directory

$ mkdir some-directory

The mkdir command creates a new empty directory in the current path.

8.rm: Delete Files/Directories

$ rm [options] someFile

The rm command is used to delete a file or directory.

Options:

• -i prompts for confirmation before deleting each file.
• -f forces deletion without prompting for confirmation, even if the file is read-only.
• -r recursively deletes directories and their contents.

8.1 rmdir: Delete Empty Directories

$ rmdir some-directory

If the directory is empty, this command will delete the directory. Otherwise, it will return a prompt xxx not empty:

9. tail: View Contents of a Document

$ tail [options] somefile

By default, it displays the last 10 lines of the document.

Common parameters include:

• -f, which reads continuously.

  tail -f notes.log

  This command displays the last 10 lines of the notes.log file. As lines are added to notes.log, tail will continue to display them. The display continues until you press (Ctrl-C) to stop.

• +, shows from a specific line to the end.

  tail +20 notes.log

  Displays the contents of notes.log from line 20 to the end of the file.

• -c, shows the last xx lines.

  tail -c 10 notes.log

  Displays the last 10 characters of the notes.log file:

The tail command is useful for viewing crash reports or historical logs:

# tail /var/log/messagesMar 20 12:42:22 hameda1d1c dhclient[4334]: DHCPREQUEST on eth0 to 255.255.255.255 port 67 (xid=0x280436dd)Mar 20 12:42:24 hameda1d1c avahi-daemon[2027]: Registering new address record for fe80::4639:c4ff:fe53:4908 on eth0.*.Mar 20 12:42:28 hameda1d1c dhclient[4334]: DHCPREQUEST on eth0 to 255.255.255.255 port 67 (xid=0x280436dd)Mar 20 12:42:28 hameda1d1c dhclient[4334]: DHCPACK from 10.76.198.1 (xid=0x280436dd)Mar 20 12:42:30 hameda1d1c avahi-daemon[2027]: Joining mDNS multicast group on interface eth0.IPv4 with address 10.76.199.87.Mar 20 12:42:30 hameda1d1c avahi-daemon[2027]: New relevant interface eth0.IPv4 for mDNS.Mar 20 12:42:30 hameda1d1c avahi-daemon[2027]: Registering new address record for 10.76.199.87 on eth0.IPv4.Mar 20 12:42:30 hameda1d1c NET[4385]: /sbin/dhclient-script : updated /etc/resolv.confMar 20 12:42:30 hameda1d1c dhclient[4334]: bound to 10.76.199.87 -- renewal in 74685 seconds.Mar 20 12:45:39 hameda1d1c kernel: usb 3-7: USB disconnect, device number 2

10. find: Search for Files

$ find path -name filename

The find command can quickly locate files or directories. This feature is useful when you are working on large projects with hundreds of files and multiple directories.

To find all files named index.js:

To find files of a specific type:

$ find . -name "*.js"

11. mv: Move Files

$ mv somefile /to/some/other/path

The mv command moves a file or directory from one location to another.

It supports moving single files, multiple files, and directories.

12. wget: File Downloading Tool

$ wget someurl

wget is a free software package for retrieving files using HTTP, HTTPS, FTP, and FTPS (the most widely used Internet protocols).

It is a non-interactive command-line tool, making it easy to call from scripts, CRON jobs, and terminals that do not support X-Windows.

wget has many features that make it easy to retrieve large files or mirror entire Web or FTP sites, including:

• Can resume aborted downloads using REST and RANGE.
• Can use filename wildcards and recursively mirror directories.
• NLS-based message files for multiple languages.
• Can convert absolute links in downloaded documents to relative links so that downloaded documents can link locally.
• Runs on most UNIX-like operating systems as well as Microsoft Windows.
• Supports HTTP proxies, cookies, and persistent HTTP connections.
• Unattended/background operation.

13. tree: List Directory Contents in Tree Format

When writing documentation, you often need to list the file directory structure, and the tree command can help with that. The tree command may not be available on some Linux and macOS systems, and you need to install it:

1. First, ensure that Homebrew is installed; if not, run:

   /usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"

2. Install the tree command

brew install tree

Results:

(base) xxx$ tree.├── djangoStudy│   ├── __init__.py│   ├── settings.py│   ├── urls.py│   └── wsgi.py└── manage.py
1 directory, 5 files

14. “|“: Pipe Command

Usually, we can only execute one command in the terminal and press enter to execute it. So how do we execute multiple commands?

• To execute multiple commands in sequence: command1;command2;command3; simple sequential instructions can be achieved using ;.
• To conditionally execute multiple commands: which command1 && command2 || command3
• &&: If the previous command succeeds, execute the next command, consistent with usage in JavaScript.
• ||: Opposite to &&, executes the next command if the previous one fails.
• $?: Stores the return result of the last command.

// Example: $ which git>/dev/null && git --help  // If the git command exists, execute git --help command$ echo $?

The pipe command can link the output of various commands as input for the next, making chained operations simple.

A pipe is a communication mechanism, usually used for inter-process communication (it can also be done via sockets for network communication). It manifests as the output (stdout) of each preceding process directly as the input (stdin) for the next process.

 $ command1 | command2 | …

Considerations for pipe commands:

• Can only handle the correct output of the previous command, cannot handle error output;
• The last command must be able to receive standard input stream commands to execute.

Examples: 1. Display detailed information about the contents of the /etc directory:

$ ls -l /etc | more

2. Input a string into a file:

$ echo "Hello World" | cat > hello.txt

Conclusion & References

• Here Are 11 Console Commands Every Developer Should Know^[1]
• Linux Pipe Command^[2]
• Using the Tree Command on macOS^[3] Here’s a powerful Linux command table

References

[1]

Here Are 11 Console Commands Every Developer Should Know: https://medium.com/better-programming/here-are-11-console-commands-every-developer-should-know-54e348ef22fa

[2]

Linux Pipe Command: https://www.jianshu.com/p/9c0c2b57cb73

[3]

Using the Tree Command on macOS: https://www.jianshu.com/p/f540e8b6e53f

Author: Frontend Dissuader, Full Stack Developer, focused on sharing knowledge in frontend & Python domains, with a blog accumulating over 1 million views. Gold Digger Community, Zhihu Column, WeChat Official Account 【Frontend Dissuader】

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