Portable Shell Syntax is the scripting language syntax used by the System V Bourne shell. This syntax is compatible with the heirloom shell and is the syntax documented in most Unix books. Examples marked "Works with: Bourne Shell" should work in any of the Bourne-compatible shells.
A Bourne Shell script begins with a shebang (also known as a hashbang) like this, which tells the operating system to use the Bourne compatible shell interpreter:
In 2009, Computerworld published an in-depth interview with Steve Bourne, The A-Z of Programming Languages: Bourne shell, or sh, which details the Bourne shell origins and design decisions.
Bourne Shell and Heirloom Shell have problems with here documents. Here is one such problem. A substitution, inside a here document, inside backquotes, inside double quotes, does insert too many backslashes.
expr "`f string`"
# Output from Bourne Shell: here \s\t\r\i\n\g
# Correct output: here string
The workaround is to move the backquotes to an assignment.
# Output: here string