Certainly, it is the last thing we can see within Windows that reminds us of what was MS-DOS. However, what we do have to disagree on is its usefulness. Indeed, the possibilities it offers are almost endless. In fact, it has an enormous scope, something that many people ignore. But not everything stays there. In fact, it can even be fun to use the Command Prompt, or at least a lot more fun than we might imagine. Let’s take a look at some unexpected, amusing, and even bizarre features hidden in the Command Prompt.

Customize the appearance

Although you may find it strange, the command prompt can be customized: You can change the background color, the tab name, search for text and more. To do so, the following must be done:

• We enter the Command Prompt by typing the same in the search area of the taskbar and clicking Open when the option comes up.
• Right-click on the Command Prompt icon in the upper left corner of the screen.
• We will see how we can select Color (to change the color of the Command Prompt), Rename Tab, Duplicate Tab, Split Table, Export Text and Search (to search for a particular text).

Window title

The title of the window can be changed with one command and, moreover, in an extremely simple way. To do it, we must put title. Then, we will write the word or phrase that we want to appear in the header of the Command Prompt window. It has a limited utility. However, it is true that it is a curious function. Besides that, few people know about the Windows Command Prompt.

Where your data goes

This is a fun and interesting trick. Indeed, it can be used for networking and problem-solving. The tracert command, followed by an IP address or a website, will show a list of where our connection bounces to on the way to that address. It is really curious to see all the stops our connection makes on its way to the destination we have marked.

The normal thing is that the configuration of Internet of our house send us to several addresses related to the ISP to later depend on where we are going to go. In fact, each website transfers data differently. This depends on where the website itself connects from and where we are finally going to get to.

Turning off the computer

We are also going to be able to turn off the computer thanks to the Command Prompt. This can be useful if there is an incident that does not let Windows do it. Also, if we do not want to force it by means of the physical button of the device.

To shut down the computer, we must put the following command: shutdown/s. If what we want is to restart the computer at that precise moment, what we will have to write is: shutdown/r This way of turning off the computer may not be practical. However, it may come in handy at some point. So it is not a bad thing to have this information.

Imagine that this curious Command Prompt trick is the one that allows you to shut down or restart your computer at a time when you have a problem. Then it won’t seem so trivial.

Star Wars

This is a really different trick that will generate a lot of curious looks when we show it to someone. To view Star Wars in the Command Prompt, we must enable a service called Telnet. If you have Windows 10 or 11, press Win + Q, type telnet. Then select Turn Windows features on or off.

After that, we go down to the Telnet Client entry, check the box, then click OK and close the window.

Re-enter the Command Prompt and execute the following commands, pressing Enter after each one:

• telnet telehack.com
• starwars

Then you just have to enjoy looking at the screen, since we will have the story of Star Wars Episode IV totally made by ASCII. Undoubtedly, something curious, fun and, for many users, even entertaining.

Command Prompt Aquarium

If we continue using Telnet we can not only have Star Wars on the screen, but more possibilities. As soon as we start with the telnet command telehack.com, we see that there are many more options, but the one we are going to see next is possibly the best achieved.

The most remarkable thing next to the Star Wars ASCII recreation is the aquarium command. If we put this command as we did in the previous case (instead of putting starwars) we will see an ASCII aquarium that could even be used as a screensaver.

With all these tricks, you will have witnessed that the Windows Command Prompt has many practical functions for the configuration and management of the operating system. In addition to others that are very curious.

That means that the Windows Command Prompt can surprise you much more than you might expect with these curious tricks. The truth is that fun can be found in the most unlikely places.

The post Command Line Magic: Secret Features and Hidden Functions of the Windows Command Prompt appeared first on Linux Windows and android Tutorials.

The cat command is part of GNU CoreUtils and is mainly used to display by standard output the entire contents of a text file. This can be quite useful in many advanced tasks with the system, for example, sysadmin uses it quite a bit to view any file from the terminal.

On the other hand, the cat command is also used to create files because it allows you to capture standard input and assign it to an empty file. Of course, this possibility offered by the cat command is rarely used.

So let’s go for it.

The Linux cat command

Cat is a fairly simple command to use, it is also possible to use it on UNIX based systems such as FreeBSD. It has a basic syntax of use which is as follows:

cat [OPTION]… [FILE]…

However, it has other options that extend the functionality of the command. If you want to show them, just use the following command:

:~$ cat --help
Usage: cat [OPTION]… [FILE]…
 Concatenate FILE(s) to standard output.
 With no FILE, or when FILE is -, read standard input.
 -A, --show-all           equivalent to -vET
   -b, --number-nonblank    number nonempty output lines, overrides -n
   -e                       equivalent to -vE
   -E, --show-ends          display $ at end of each line
   -n, --number             number all output lines
   -s, --squeeze-blank      suppress repeated empty output lines
   -t                       equivalent to -vT
   -T, --show-tabs          display TAB characters as ^I
   -u                       (ignored)
   -v, --show-nonprinting   use ^ and M- notation, except for LFD and TAB
       --help     display this help and exit
       --version  output version information and exit
 Examples:
   cat f - g  Output f's contents, then standard input, then g's contents.
   cat        Copy standard input to standard output.
 GNU coreutils online help: http://www.gnu.org/software/coreutils/
 Full documentation at: http://www.gnu.org/software/coreutils/cat
 or available locally via: info '(coreutils) cat invocation'

But, let’s see the usefulness of the cat command using several useful examples.

Using the cat command

I will create a sample text file called file.txt and add content.

To display the contents of the file, simply use the following command:

:~$ cat file.txt

It is also possible to use an absolute route, for example:

:~$ cat /home/angelo/file.txt

So you can see the contents of a file from another directory.

It is also possible to view the contents of several files, just separate them by a blank space:

:~$ cat file.txt file2.txt

And so on.

It is also possible, to show the content of the file and display the lines it has. To do this, add the -n option.

:~$ cat -n file.txt

So we can quickly identify a particular line.

However, many text files have empty lines. This is common. The cat command also allows us to show only those that have content and are not empty. The -b option is the correct one.

:~$ cat -b file.txt

If you want to know when a line ends, the cat command can help you with the -E option.

:~$ cat -E file.txt

Also, cat can display the non-printable characters with the -v option.

:~$ cat -v file.txt

Or the tabs with the -T option

:~$ cat -T file.txt

Note: I have modified the file to include a tab and show you how it looks.

So, that is it. You already know how to use the cat command.

Conclusion

The cat command is quite simple to use but it can get us out of trouble in many cases. Especially useful if you are sysadmin or a student of some computer-related engineering, the post will help you get familiar with the terminal.

Please share this post and join our Telegram channel.

I invite you to read other posts about Linux commands:

cp command
The Tail command
head command
The wget command

The post The Linux cat command appeared first on Linux Windows and android Tutorials.

If you’re new to Linux you probably won’t like the terminal, and that’s understandable but I’m also telling you that it’s a very powerful tool and it’s not as complicated as it seems. Also, many sysadmin users use it almost every day and this is because it is very efficient.

Yes, it is true, there are more complicated commands to use but in this case, the head command is quite simple.

Introduction

The head command is the complement of the Tail command. It is used to display the first few lines of a text file. Therefore, the use of this command is very useful for sysadmin that needs to check logs constantly.

Like the Tail command, the head command belongs to GNU utils which is a range of tools for processing files and folders by the terminal. So this command is for sure available in your favorite Linux distribution.

Now we will show you how to use it with some simple examples.

Using the Linux Head command

The Head command is one of the simplest there is. The basic syntax of the command is as follows:

~$ head [OPTION]... [FILE]..

As you can see there are options that alter the behavior of the command. To see all the available options, just use this command:

:~$ head --help

And as you can see in the image, they are few and this reaffirms what I said about it being a pretty simple command to use.

To better demonstrate the use of the command, I have created a text file called example.txt and added certain names.

option. For example, display the first 3 lines of the file.

:~$ head -n 3 example.txt

We can even use the head command to display a number of bits of the file. This is made possible by the -c option.

:~$ head -c 10 example.txt

Finally, it is possible to use the -v option to display the title of the file. Use it in some cases.

:~$ head -v example.txt

And well, that’s it. The head command is quite useful and simple to use and using it with the tail command makes an extraordinary combination.

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Introduction

Rsync, remote synchronize is known as a remote synchronization function of the software, it synchronizes files at the same time, can maintain the original file permissions, time, hard and soft links and other additional information. it is a “sync algorithm” that provides a quick way to synchronize files between clients and remote file servers, and can also be transferred via SSH, which is also very confidential, supports breakpoint continuation, data can be pushed or pulled, and is free of chargeS.

Rsync advantages：

• Ability to update entire directories and trees and file systems;
• Selectively maintain symbolic links, hard links, file ownership, permissions, devices, and time for folders and files;
• For installation, there are no special permission requirements;
• For multiple files, the internal pipeline reduces the file wait delay;
• Can use RSH, SSH or direct port as the transfer port;
• Support anonymous Rsync synchronization files are the ideal mirror tool;

Installation

Installing rsync is pretty easy, it doesn’t rely on any special libraries at all, so you can install it directly with yum.

yum install -y rsync 

The command rsync will appear once the installation is complete

Rsync works

Rsync works in three ways：
1.synchronization on the local file system.
2.the local host USES the remote shell to communicate with the remote host.
3.localhost connects rsync daemon on a remote host via network socket.

Here is the syntax works for each rsync:

Local:  
      rsync [OPTION...] SRC... [DEST]   
Access via remote shell:   
      Pull: rsync [OPTION...] [USER@]HOST:SRC... [DEST]   
      Push: rsync [OPTION...] SRC... [USER@]HOST:DEST   
Access via rsync daemon:   
      Pull: rsync [OPTION...] [USER@]HOST::SRC... [DEST]         
            rsync [OPTION...] rsync://[USER@]HOST[:PORT]/SRC... [DEST]   
      Push: 
            rsync [OPTION...] SRC... [USER@]HOST::DEST         
            rsync [OPTION...] SRC... rsync://[USER@]HOST[:PORT]/DEST 

Option

man rsync

Options
 -v, --verbose               increase verbosity
 -q, --quiet                 suppress non-error messages
     --no-motd               suppress daemon-mode MOTD (see manpage caveat)
 -c, --checksum              skip based on checksum, not mod-time & size
 -a, --archive               archive mode; equals -rlptgoD (no -H,-A,-X)
     --no-OPTION             turn off an implied OPTION (e.g. --no-D)
 -r, --recursive             recurse into directories
 -R, --relative              use relative path names
     --no-implied-dirs       don't send implied dirs with --relative
 -b, --backup                make backups (see --suffix & --backup-dir)
     --backup-dir=DIR        make backups into hierarchy based in DIR
     --suffix=SUFFIX         set backup suffix (default ~ w/o --backup-dir)
 -u, --update                skip files that are newer on the receiver
     --inplace               update destination files in-place (SEE MAN PAGE)
     --append                append data onto shorter files
     --append-verify         like --append, but with old data in file checksum
 -d, --dirs                  transfer directories without recursing
 -l, --links                 copy symlinks as symlinks
 -L, --copy-links            transform symlink into referent file/dir
     --copy-unsafe-links     only "unsafe" symlinks are transformed
     --safe-links            ignore symlinks that point outside the source tree
 -k, --copy-dirlinks         transform symlink to a dir into referent dir
 -K, --keep-dirlinks         treat symlinked dir on receiver as dir
 -H, --hard-links            preserve hard links
 -p, --perms                 preserve permissions
 -E, --executability         preserve the file's executability
     --chmod=CHMOD           affect file and/or directory permissions
 -A, --acls                  preserve ACLs (implies --perms)
 -X, --xattrs                preserve extended attributes
 -o, --owner                 preserve owner (super-user only)
 -g, --group                 preserve group
     --devices               preserve device files (super-user only)
     --copy-devices          copy device contents as regular file
     --specials              preserve special files
 -D                          same as --devices --specials
 -t, --times                 preserve modification times
 -O, --omit-dir-times        omit directories from --times
     --super                 receiver attempts super-user activities
     --fake-super            store/recover privileged attrs using xattrs
 -S, --sparse                handle sparse files efficiently
 -n, --dry-run               perform a trial run with no changes made
 -W, --whole-file            copy files whole (without delta-xfer algorithm)
 -x, --one-file-system       don't cross filesystem boundaries
 -B, --block-size=SIZE       force a fixed checksum block-size
 -e, --rsh=COMMAND           specify the remote shell to use
     --rsync-path=PROGRAM    specify the rsync to run on the remote machine
     --existing              skip creating new files on receiver
     --ignore-existing       skip updating files that already exist on receiver
     --remove-source-files   sender removes synchronized files (non-dirs)
     --del                   an alias for --delete-during
     --delete                delete extraneous files from destination dirs
     --delete-before         receiver deletes before transfer, not during
     --delete-during         receiver deletes during the transfer
     --delete-delay          find deletions during, delete after
     --delete-after          receiver deletes after transfer, not during
     --delete-excluded       also delete excluded files from destination dirs
     --ignore-errors         delete even if there are I/O errors
     --force                 force deletion of directories even if not empty
     --max-delete=NUM        don't delete more than NUM files
     --max-size=SIZE         don't transfer any file larger than SIZE
     --min-size=SIZE         don't transfer any file smaller than SIZE
     --partial               keep partially transferred files
     --partial-dir=DIR       put a partially transferred file into DIR
     --delay-updates         put all updated files into place at transfer's end
 -m, --prune-empty-dirs      prune empty directory chains from the file-list
     --numeric-ids           don't map uid/gid values by user/group name
     --timeout=SECONDS       set I/O timeout in seconds
     --contimeout=SECONDS    set daemon connection timeout in seconds
 -I, --ignore-times          don't skip files that match in size and mod-time
     --size-only             skip files that match in size
     --modify-window=NUM     compare mod-times with reduced accuracy
 -T, --temp-dir=DIR          create temporary files in directory DIR
 -y, --fuzzy                 find similar file for basis if no dest file
     --compare-dest=DIR      also compare destination files relative to DIR
     --copy-dest=DIR         … and include copies of unchanged files
     --link-dest=DIR         hardlink to files in DIR when unchanged
 -z, --compress              compress file data during the transfer
     --compress-level=NUM    explicitly set compression level
     --skip-compress=LIST    skip compressing files with a suffix in LIST
 -C, --cvs-exclude           auto-ignore files the same way CVS does
 -f, --filter=RULE           add a file-filtering RULE
 -F                          same as --filter='dir-merge /.rsync-filter'
                             repeated: --filter='- .rsync-filter'
     --exclude=PATTERN       exclude files matching PATTERN
     --exclude-from=FILE     read exclude patterns from FILE
     --include=PATTERN       don't exclude files matching PATTERN
     --include-from=FILE     read include patterns from FILE
     --files-from=FILE       read list of source-file names from FILE
 -0, --from0                 all *-from/filter files are delimited by 0s
 -s, --protect-args          no space-splitting; only wildcard special-chars
     --address=ADDRESS       bind address for outgoing socket to daemon
     --port=PORT             specify double-colon alternate port number
     --sockopts=OPTIONS      specify custom TCP options
     --blocking-io           use blocking I/O for the remote shell
     --stats                 give some file-transfer stats
 -8, --8-bit-output          leave high-bit chars unescaped in output
 -h, --human-readable        output numbers in a human-readable format
     --progress              show progress during transfer
 -P                          same as --partial --progress
 -i, --itemize-changes       output a change-summary for all updates
     --out-format=FORMAT     output updates using the specified FORMAT
     --log-file=FILE         log what we're doing to the specified FILE
     --log-file-format=FMT   log updates using the specified FMT
     --password-file=FILE    read daemon-access password from FILE
     --list-only             list the files instead of copying them
     --bwlimit=KBPS          limit I/O bandwidth; KBytes per second
     --write-batch=FILE      write a batched update to FILE
     --only-write-batch=FILE like --write-batch but w/o updating destination
     --read-batch=FILE       read a batched update from FILE
     --protocol=NUM          force an older protocol version to be used
     --iconv=CONVERT_SPEC    request charset conversion of filenames
     --checksum-seed=NUM     set block/file checksum seed (advanced)
 -4, --ipv4                  prefer IPv4
 -6, --ipv6                  prefer IPv6
     --version               print version number
(-h) --help                  show this help (-h is --help only if used alone)

Although there are many options, the most common combination of options is “avz”, which compresses and displays some information and transmits it in archive mode.

Use of rsync

Synchronize data on the local disk

The following commands synchronize individual files on your local computer from one location to another.

rsync -zvh backup.tar /tmp/backup/

We can use it ‘–progress ‘option. It shows the file that was transferred and the time remaining.

rsync -zvh backup.tar /tmp/backup/ --progress

The commands will transfer or synchronize all files in the same directory to different directories on the same computer.

rsync -avzh /root/tomcat/ /tmp/backup/tomcat/ --progress

Use the –include and –exclude options

These two options allow us to include exclude files and folders by specifying parameters with which these options can help us specify which files and folders to include and exclude during synchronization. You do not want to be moved to these files or directories.
Here, in this example, the rsync command will include only those files and directories that end with a “log” and exclude end with a “war” files and directories.

rsync -avzh  --include '*log' --exclude '*war' /root/tomcat/ /tmp/backup/tomcat/ --progress

Use the –delete

If the file or directory does not exist at the source but already exists at the destination, you may need to delete the existing file/directory at the destination during synchronization.

We can use the ‘–delete’ option to delete files that do not exist in the source directory. Source and target are synchronized. Now, create a new target file, test.txt.

touch /tmp/backup/tomcat/123.txt
ls /tmp/backup/tomcat/          
rsync -avzh --delete  /root/tomcat/ /tmp/backup/tomcat/ --progress
ls /tmp/backup/tomcat/                                            

The target has the name test.txt, and when synchronizing the new file with the source of the ‘-delete’ option, it removes the file test.txt.

Sets the maximum size of the file to transfer

You can do this with the — max-size option. Here, in this example, the maximum file size is 200K, so the command will only pass smaller files equal to or greater than 200K.

rsync -avzh --max-size='200k'  /root/tomcat/ /tmp/backup/tomcat/ --progress

Set bandwidth limits and transfer files

You can transfer data from one machine to another at the same time with the help of the ‘–bwlimit’ option. This option helps limit I/O bandwidth.

rsync -avzh --bwlimit=10  /root/tomcat/ /tmp/backup/tomcat/ --progress
rsync -avzh --bwlimit=50  /root/tomcat/ /tmp/backup/tomcat/ --progress

Remotely synchronize data using ssh-based rsync

Through the introduction of synchronizing data on a local disk, we learned about the most common options. The options for remote transport are the same as for local transport. So we’ll cover only the basic format of remote transmission. If you need to use other options, you can choose according to the above description

Use SSH to copy files from the local server to the remote server

To specify the protocol to use rsync, you need to give the protocol you want to use the “-e” option. Here, in this example, we will use “SSH” with the “-e” option “-p” to specify the transport port and perform the data transfer.

rsync -zvh -e "ssh -p12598" backup.tar root@172.16.6.250:/tmp/backup/ --progress

Copy files from remote server to local server via SSH

rsync -zvh -e "ssh -p12598"  root@172.16.6.250:/tmp/backup/*  /tmp/  --progress

conclusion

The above article introduced two working modes of rsync: local transmission and remote transmission via SSH protocol. The third working mode is transmission via rsync Daemon. Rsync Daemon commands are basically the same as using SSH. The only change is that the destination address is transferred according to the alias defined in Rsync Daemon instead of IP.

If you want to know more about rsync, please leave me a message To learn more about Linux, please follow my link. Thank you

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What is a system service?

A system service is usually an application that runs in the background. That is to say that it is not necessary that they have a constant interaction with the user to be able to work. This concept is vital to any modern operating system. Some of the most essential applications of a server are managed as services, for example, SSH or MySQL.

Well, services are handled in Linux with a command that is systemctl. This is because, since recent versions of the kernel and the main current Linux distributions, Systemd is in charge of managing the services.

So we will see how to use the Linux systemctl command.

The Linux systemctl command

Within our Linux system, the main function of the systemctl command is to administer the system services. Or those applications that are managed as a service.

First, it is a command that requires root privileges to function. This means that either we enable sudo for our user or we will have to be the root user.

How to enable sudo on Debian 10?

How to enable sudo on CentOS 8?

Now, we will be able to list all the services that are in our system, for it uses the following command

:~# systemctl -t list-unit-files --all

It is also useful to list all active services. To do this, just use:

:~# systemctl list-unit

Once we know what the services are, we can work with them.

To start a service that is stopped the syntax is as follows:

:~# systemctl start [service_name]

For example:

:~# systemctl start apache2

To stop it:

:~# systemctl stop [service_name]

Sometimes we make changes to the service and for them to take effect it is necessary to restart it. To do this, we use the following command:

~# systemctl restart [service_name]

However, many of these changes are at the configuration level. In this case, the service has to be recharged.

:~# systemctl reload [service_name]

It is also possible to restart a service that is currently running:

:~# systemctl condrestart [service_name]

And if you want to know the status of a service:

:~# systemctl status [service_name]

This function is quite interesting about the status of the service. Because we will be able to have in detail if a service is running or not. And if at the moment of initiating it gives an error, also with this command we will be able to make the pursuit of him.

If you want a service to run automatically with the system, you can do it with the following command:

:~# systemctl enable [service_name]

If you no longer wish it to be so, reverse it with this other command:

:~# systemctl disable [service_name]

And that is it. I hope this little guide can help you with systemctl.

Conclusion

Using and managing the system’s services on Linux is not a completely simple task, but it is not as difficult as we think. In this sense, systemctl is a relatively simple command that will help us with the management of them.

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NMAP is a popular network scanning and sniffing tools is also a powerful tool for port scanning type safety assessment, is widely used in the security scan, NMAP is a useful online tool, also is often used in the production and development, mainly for port open view of detection and LAN information collection, etc., different Linux distributions generally also with NMAP package management tool, can also choose to go to the website to download the source code package compiled installation.

Install nmap

In case, you are unable to use nmap command, use below command to install it

 centos：yum install nmap
 ubuntu：apt-get install nmap  

Check that the installation is successful

 nmap -v

Nmap usage method

• Scan IP which common TCP port and UDP port are open

nmap 127.0.0.1 or nmap -sS -sU -p 1-65535 127.0.0.1

• Scan multiple IP addresses or subnet

nmap 127.0.0.1 172.16.6.1
nmap 172.16.6.1-100
nmap 172.16.6.0/24  

In the scan result, if the state column is open, it means the state is open; if it is filtered, it may be filtered by a firewall; if it is closed, it means the port is closed.

• Scans which hosts are alive in the subnet

nmap -n -sP 172.16.6.0/24

• Nmap route trace

namp –traceroute 8.8.8.8  

• Scans IP or subnet hosts for port

nmap -p 12598 127.0.0.1
nmap -p 12598 172.16.6.0/24

• An option that goes one step further and gives you more information about the services running on a specific host is ‘-A’.

nmap -A 127.0.0.1

• Nmap scans the operating system type using the -O option

nmap -O 12598 127.0.0.1

• For an in-depth understanding of the use of the nmap command, use it to examine the man pages

man nmap

Conclusions

nmap is one of those utilities that have so many options and capabilities, it can actually be overwhelming. As is the case with those types of utilities, you will end up using only a fraction of its capabilities to help get a specific job done. If you want to use it at its full potential, you’re in for a lot of trial and error and some hands-on experience with real networks.

So, you can read our post abour networks in this link.

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Ss is an abbreviation for Socket Statistics. As the name suggests, the ss command can be used to get socket statistics, which can display something similar to netstat. The advantage of ss is that it can display more detailed information about TCP and connection status, and is faster and more efficient than netstat.

When the number of socket connections on the server becomes very large, either using the netstat command or directly cat /proc/net/tcp, the execution speed will be slow.

The secret of ss is that it uses tcp_diag in the TCP stack. Tcp_diag is a module for analyzing statistics, which can get the first-hand information in the Linux kernel, which ensures the fast and efficient ss.

Intsall ss

In case, you are unable to use ss command, use below command to install it.

 yum install iproute iproute-doc 

Now it is installed and ready to use.
Below are some useful commands to monitor network connections.

List all socket connections

The basic ss command, with no options, lists only all connections, no matter what state they are in.

ss

List only TCP Ports connections

To see all TCP socket connections, use the -lt option

ss -lt 

List only UDP Ports connections

To see all UDP socket connections, use the -ua option

ss -ua

Display socket PID (process ID)

To display the process ID associated with the socket connection, use the -p option

ss -p

Display summary statistics

To list summary statistics, use the -s option

ss -s

Filter connections by port number

The ss command also allows you to filter socket port Numbers or address Numbers

ss -at '( dport = :12598 or sport = :12598 )' 

Check the ss commands in the man page

For an in-depth understanding of the use of the ss command, use it to examine the man pages

man ss

These are some of the common options used with the ss command. This command is considered more advanced than the netstat command and provides detailed information about the network connection.

In conclusion:The ss command is a tool for displaying network socket-related information on a Linux system. The tool displays more details about the netstat command used to display active socket connections.

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CURL is a command line tool and library for transferring data with URLs. Many download scripts or file transfers use CURL as a means to achieve this. In addition, CURL supports FTP, FTPS, Gopher, HTTP, HTTPS, IMAP, IMAPS, LDAP and many other protocols quite popular on networks.

On the other hand, the use of CURL is not limited exclusively to computers but to other devices that use UNIX such as cell phones, cars and is the transfer backend of many of the most popular applications in the world.

Using CURL command on Linux

The idea of this post is to show the use of CURL, not to do it in a theoretical way. The main idea is to do it through examples that demonstrate its use.

So, let’s start.

1. Install CURL

Obviously, the first step is to install CURL. It is really simple as it is available in the official repositories of most Linux distributions. So, its installation is limited to a single command.

For Debian, Ubuntu, Linux Mint and derivates

:~$ sudo apt install curl

If you use Fedora:

:~$ sudo dnf install curl

For CentOS and RHEL:

:~$ yum install curl

2. Check the CURL version

The second thing you should do is, check the CURL version. Important to know what news you have available. While it is not essential to have CURL updated to its latest version, it is also not crazy to do so.

:~$ curl --version

3. Display the content of an HTML

A simple way to display the source code of an HTML site from the terminal is with CURL.

:~$ curl http://website.com/page.html

Of course, it is necessary that you place the complete website of your preference.

4. Download a file with CURL

This is one of the most common uses we give to CURL. Downloading a file is a really simple task.

:~$ curl -O https://pixabay.com/en/photos/download/ocean-3605547_1280.jpg

You can use the -o option to specify the name of the downloaded file.

:~$ curl -o image.jpg https://pixabay.com/en/photos/download/ocean-3605547_1280.jpg

I remind you again that, I’m using test URLs, you have to enter yours.

5. Use a proxy

With CURL it is possible to make connections through a proxy. The proxy may or may not require authentication.

:~$ curl -x your-proxy:8080 -U user_password -O http://domain.com/file

In case the proxy server does not need authentication, you can omit the option -U.

6. Get HTTP header information from a website

There are occasions when it is necessary to know the information stored in the HTTP headers of some website. It is really easy to do it with CURL.

:~$ curl -I http://website.com

7. Limit download rate

If you are connected using mobile data or simply want to limit the CURL download rate, you can do it easily.

:~$ curl --limit-rate 100K -O http://domain.com/file.file

8. Download file from an FTP server

As I said at the beginning of this post, CURL supports many protocols, not only HTTP but also FTP. Now I will show you how to do it.

:~$ curl -u username:password -O ftp://ftpserver/file.zip

In case you do not need authentication, omit the option -u.

9. Upload Files to an FTP server

You can also upload files to an FTP server. The syntax is similar only this time, you should add the -T option.

:~$ curl -u username:password -T myfilepath.jpg ftp://ftpserver/file.zip

Note: I’m using false addresses and that’s why CURL can’t find them. But don’t worry that the commands are correct.

10. Check the CURL help

Of course, the use of the CURL command is very extensive and I only demonstrated some of its uses. For more information about the CURL command, it is convenient to consult its help from the terminal.

:~$ curl --help

And that’s it.

Conclusion

I hope this article has made clear to you the potential of CURL. There is so much potential that there is still so much to show, but I think the objective has been achieved.

CURL is widely used in script automation of content downloads and is not only used in computer equipment but in many others.

So, if you liked the article share it through your social networks.

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