The Shell Game 151Simple quoting barely works in the C Shell because no contract exists
between the shell and the programs it invokes on the users’ behalf. For
example, consider the simple command:
grep string filename:The string argument contains characters that are defined by grep, such
as?, [, and], that are metasyntactic to the shell. Which means that you
might have to quote them. Then again, you might not, depending on the
shell you use and how your environment variables are set.
Searching for strings that contain periods or any pattern that begins with a
dash complicates matters. Be sure to quote your meta character properly.
Unfortunately, as with pattern matching, numerous incompatible quoting
conventions are in use throughout the operating system.
The C Shell’s metasyntatic zoo houses seven different families of metasyn-
tatic operators. Because the zoo was populated over a period of time, and
the cages are made of tin instead of steel, the inhabitants tend to stomp over
each other. The seven different transformations on a shell command line
are:
As a result of this “design,” the question mark character is forever doomed
to perform single-character matching: it can never be used for help on the
command line because it is never passed to the user’s program, since Unix
requires that this metasyntactic operator be interpreted by the shell.
Having seven different classes of metasyntactic characters wouldn’t be so
bad if they followed a logical order of operations and if their substitution
rules were uniformly applied. But they don’t, and they’re not.
Aliasing alias and unalias
Command Output Substitution `
Filename Substitution *, ?, []
History Substitution !, ^
Variable Substitution $, set, and unset
Process Substitutuion %
Quoting ',"