Quick and Easy File Transfer with netrw

Fast Transport

© Lead Image © Tomas Anderson, 123RF.com

© Lead Image © Tomas Anderson, 123RF.com

Article from Issue 163/2014

Even without elaborate infrastructure, you can still push your data across the network with netrw.

If you're looking for a quick and easy tool for transferring files, netrw [1] offers an elegant solution. According to the project website, the purpose of netrw is to "simplify and speed up file transfers to hosts without an FTP server." Netrw is also useful for scenarios where the user transferring the file does not have an account on the target machine.

The netrw project consists of two programs, netread and netwrite. As the names imply, netwrite writes the file from the sending machine and netread reads it on the target. The advantage of this ad hoc solution, compared with solutions in which the daemon listens constantly, is the brief existence of the open channel. This design reduces the likelihood of an attacker accidentally stumbling across the open port.

Netrw gives you the ability to transfer any kind of electronic data. Of course, it's always better to use netrw on a protected network, and you are advised not to use it in an insecure setting. If you do, however, you'll want to protect your privacy by encrypting the payload.

Basic Functions

In the simplest case, start by initializing the reception of data with netread. You only specify the port number and redirect stdout to a file (Listing 1, line 1). The transfer itself is launched in the same style (line 2).

Listing 1

Configuring Data Reception


Figure 1 shows the transfer sequence. The two programs have common options; the most important ones are described in Table 1.

Figure 1: With only a few parameters, you can transfer data using the netread and netwrite tools.

Table 1

Options for netread and netwrite




Uses UDP instead of TCP

-f <Host>

Establishes a connection on the read side

-C <Algorithm>

Uses specified algorithm (sha1, md5, rmd160, none)

-o <File>

Specifies the file

-h <Value>

Outputs the progress of all <Value>s (KB)

-H <Value>

Outputs the progress of all <Value>s (MB)


Specifies speed in bps (instead of Bps)


Suppresses screen output


Outputs detailed messages


Outputs very detailed messages

You can either redirect the payload directly from a file or you can use the -i <file> option in netwrite. On the target system, use the output redirection (>) or the -o <file> option for saving the data.


The progress indicator proves especially useful for transferring large volumes of data; it lets you check to see whether bytes are actually still flowing across the network. You can choose between a display in kilobytes (-h) or megabytes (-H). The option requires you to define the volume of data that triggers a hash mark being written to screen. This can mean that your screen either fills up or shows very little information (Figure  2).

Figure 2: Because the progress indicator responds flexibly to a parameter, it is essential to choose a meaningful value for the data volume.

In a shell script (Listing 2) [2], you could use stat [3] to determine the size of the file and then define a useful integer value for the progress bar. Note that one line is made up of 50 hash marks. Accordingly, you might not see any output for very small volumes of data.

Listing 2

Determining File Size


The receiving side does not know the file size in advance. You can either ask for this value before the transfer is initiated or use a value of 1000; experience has shown that -H produces reasonable output.

Figure 3 shows the flow of the script. For clarity, positional parameters are used in place of input templates. You could extend this script accordingly with the capabilities of Zenity [4] or cdialog  [5].

Figure 3: Script flow.

Firewall Mode

Firewall mode lets you set up a connection in the reverse direction. You can pass in either the IP address or a hostname using the -f option. The following workflow has proved useful in practical terms: Call netwrite with the -f option, then start netread also with -f. This means that you are using firewall mode on both systems, but the startup sequence is the other way around.

In Figure 4, you can see the steps required for the sender (light background in the terminal) and the receiver (dark background). The computers are addressed by their hostnames (ze5 and ZE6). After the call to netwrite, you will see a message that the program is listening on the specified port. The other messages are displayed after calling netread on the target system.

Figure 4: Data transmission flow in the firewall mode. Here, the reading side opens the connection after the program has been started on the sending side.

Buy this article as PDF

Express-Checkout as PDF
Price $2.95
(incl. VAT)

Buy Linux Magazine

Get it on Google Play

US / Canada

Get it on Google Play

UK / Australia

Related content

  • System Monitoring

    Off-the-rack monitoring tools often offer too many functions or fail to offer precisely what you need, but shell scripts let you create individual monitoring routines.

  • Zenity Dialogs

    The Zenity command-line utility lets you create simple dialog boxes with your own data or with the output of utilities and applications.

  • TGXf Project Warns of File Transfer through Screen Pixels

    Weird data transfer technique avoids all standard security measures.

  • ExifTool and jExifToolGUI

    ExifTool lets you modify and analyze metadata in multimedia files from the command line, but its comprehensive feature set results in a lengthy learning curve. Luckily, jExiftoolGUI offers an intuitive interface that makes using ExifTool easier, even for less experienced users.

  • Zenity and KDialog

    Zenity and KDialog let you integrate your scripts with the native KDE or Gnome environment.

comments powered by Disqus
Subscribe to our Linux Newsletters
Find Linux and Open Source Jobs
Subscribe to our ADMIN Newsletters

Support Our Work

Linux Magazine content is made possible with support from readers like you. Please consider contributing when you’ve found an article to be beneficial.

Learn More