The Free On-line Dictionary of Computing (30 December 2018):
("Shell archive", after ar and tar)
Any of the many Unix programs that creates a flattened
representation of one or more files, with the unique property
that it can be unflattened (the original files extracted)
merely by feeding it through a standard Unixshell. The
output of shar, known as a "shar file" or "sharchive", can be
distributed to anyone running Unix, and no special unpacking
software is required.
Sharchives are intriguing in that they are typically created
by shell scripts; the script that produces sharchives is thus
a script which produces self-unpacking scripts, which may
themselves contain scripts. The disadvantage of sharchives
are that they are an ideal venue for Trojan horse attacks
and that, for recipients not running Unix, no simple
un-sharchiving program is possible; sharchives can and do make
use of arbitrarily-powerful shell features and other Unix
Different implementations of shar vary in sophistication.
Some just uuencode each input file and output commands to
uudecode the result, others include extensive checking to
make sure the files have been transferred without corruption
and that all parts of a multi-file sharchive have been
The unshar utility strips off mail and news headers before
passing the remainder of its input to sh.