The shell referred to in these pages is always a Bourne-type shell;
that is, a shell whose syntax is based on the Unix
shell introduced by Steven Bourne in 1978 (or thereabouts), with
some later improvements. On all Unix systems, a Bourne-type shell
can be found in /bin/sh. On most modern systems, this will be somewhat
better than the Bourne shell — it will be a POSIX shell. If it
is not, there should be a POSIX-compliant shell elsewhere on the
system.
A POSIX shell is a Bourne shell with a number of extensions (which
are mostly derived from the Korn
Shell). The most important ones perform string manipulation and
integer arithmetic. In a Bourne shell, arithmetic operations require
an external program (e.g., expr, awk or
bc) as does finding the length of a string, or cutting
a string into pieces. POSIX has $((...)) for integer
arithmetic and parameter expansions for string operations.
Generally, scripts and snippets published here are designed to run in a POSIX shell. Some will run in a Bourne shell, and those that will not should not be hard to convert (in the unlikely event that you find it necessary). A few scripts require added extensions found in bash and ksh.
csh?Before POSIX shells became generally available, many people used the C shell as their interactive shell. It has a number of features that were lacking in the Bourne shell, including arithmetic and command history. However, when it comes to writing scripts, it has many drawbacks that are discussed in these three articles:
Since, as Bruce Barnett says in the first of the above articles,
"UNIX was hard enough to learn, and spending months to learn two
shells seemed silly", I recommend using a Bourne-type interactive
shell, and I specifically recommend bash.
If you need help with a csh problem, try Bruce Barnett's
csh page.
basename, dirname, grep, expr, wc...