Sending Files by E-mail

 in
When it's time to send those source files to your project leader, Linux has the commands you need.

Often, we have files we wish to send colleagues and friends by e-mail. Depending on the type of file you wish to send, there is a Linux command to make the process easy for you.

Plaintext Files

The shell archive file command shar is very useful for combining plaintext files into one file, which can then be sent by e-mail. shar writes shell commands for unpacking the output file inside the file itself, as well as code to verify the content using an MD5 checksum. It is much easier to use than the archive command tar, whose complexities can trip up even an expert. All you have to do to run shar is type:

shar input_filenames > filename.shar

It will take all the input files and write them to the output file, embedding the unpacking commands as it goes. The extension conventionally used with shar output files is .shar. To unpack the file, you don't need to know the embedded commands or retrieve them from the file yourself. Instead, use the command sh. The first argument to uuencode is the input file name; the second is the name to put in the output file header. We will use the same name for both. Type:

sh filename.shar
The sh command will do the work for you by reading the file, extracting the commands and executing them to unpack the archive.

It is permissible to use wild cards in naming your shar input files, so you can easily pack all the files in one or more directories. Just remember, the files must all be plaintext—no binaries.

The purpose of the shar command is quite similar to that of tar. However, the command and its format are much easier to remember, and since the output is plaintext instead of binary, it does not need to be encoded to send it as e-mail.

Binaries and Graphics

Non-plaintext files such as binaries and graphics must be encoded before e-mailing them. First, pack and compress your files using tar, which outputs a binary file. We won't go into tar in detail here, since it has been discussed before: see “Tar and Taper for Linux” by Yusuf Nagree, Linux Journal, February 1996 (http://www.linuxjournal.com/lj-issues/issue22/1216.html). A simple command to pack and compress all the files in the current directory would look like this:

tar -cvzf tar_files.tgz *

Now, the tar file can be encoded using the command uuencode by typing:

uuencode tar_file.tgz tar_file.tgz > mail_file
The output file can now be put into e-mail and sent off into the ether.

The recipient can save the e-mail (perhaps as mail.save) and decode the file easily—no need to even remove mail headers. Simply use the command uudecode by typing:

uudecode mail.save

uudecode will do just what its name says: decode the mail file, leaving a file called tar_file.tgz in the current directory. To unpack the tar file, type:

tar -xvzf tar_file.tgz
A single graphics file can be encoded and decoded in the same way, skipping the tar step since an archive file is not needed.

Conclusion

No matter what type of files you have, sending them to others is not a chore using these simple Linux commands.

Marjorie Richardson is Editor in Chief of Linux Journal. She has been a programmer for many years and enjoys her role as Linux advocate very much.

______________________

Webinar
One Click, Universal Protection: Implementing Centralized Security Policies on Linux Systems

As Linux continues to play an ever increasing role in corporate data centers and institutions, ensuring the integrity and protection of these systems must be a priority. With 60% of the world's websites and an increasing share of organization's mission-critical workloads running on Linux, failing to stop malware and other advanced threats on Linux can increasingly impact an organization's reputation and bottom line.

Learn More

Sponsored by Bit9

Webinar
Linux Backup and Recovery Webinar

Most companies incorporate backup procedures for critical data, which can be restored quickly if a loss occurs. However, fewer companies are prepared for catastrophic system failures, in which they lose all data, the entire operating system, applications, settings, patches and more, reducing their system(s) to “bare metal.” After all, before data can be restored to a system, there must be a system to restore it to.

In this one hour webinar, learn how to enhance your existing backup strategies for better disaster recovery preparedness using Storix System Backup Administrator (SBAdmin), a highly flexible bare-metal recovery solution for UNIX and Linux systems.

Learn More

Sponsored by Storix