The Jargon File (version 4.4.7, 29 Dec 2003):

sharchive
 /shar?ki:v/, n.

    [Unix and Usenet; from /bin/sh archive] A flattened representation of a
    set of one or more files, with the unique property that it can be
    unflattened (the original files restored) by feeding it through a standard
    Unix shell; thus, a sharchive can be distributed to anyone running Unix,
    and no special unpacking software is required. Sharchives are also
    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. Sharchives are also commonly
    referred to as ?shar files? after the name of the most common program for
    generating them.

    The downsides 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. For these reasons, this technique has
    largely fallen out of use since the mid-1990s.


The Free On-line Dictionary of Computing (30 December 2018):

shar
sharchive
shar file

    ("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 Unix shell.  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
   commands.

   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
   unpacked.

   The unshar utility strips off mail and news headers before
   passing the remainder of its input to sh.

   (1996-10-18)