shar

tool, file format ("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)