Intel XENIX 286 Programmers Guide (86) - Tenox.tc

XENIX Programming csh: C Shell
the C shell translates this to
Is -s /usr/bill
Note that the tilde (-) is a special C shell symbol that represents the user's home
directory.
Thus the alias command can be used to provide short names for commands, to provide
default arguments, and to define new short commands in terms of other commands. You
can also define aliases that contain multiple commands or pipelines, showing where the
arguments to the original command are to be substituted using the facilities of the
history mechanism. Thus the definition
alias cd 'cd \!* ; Is '
specifies an Is command after each cd command. We enclosed the entire alias definition
in single quotation marks (') to prevent most substitutions from occurring and to prevent
the semicolon (;) from being recognized as a metacharacter. The exclamation mark (!)
is escaped with a backslash (\) to prevent it from being interpreted when the alias
command is typed in. The "\!*" here substitutes the entire argument list to the
prealiasing cd com mand; no error is given if there are no arguments. The semicolon
separating commands is used here to indicate that one command is to be done and then
the next. Similarly, the following example defines a command that looks up its first
argument in the password file.
alias whois 'grep \! " /etc/passwd'
The C shell reads the .cshrc file each time it starts up. If you place a large number of
aliases there, C shells will tend to start slowly. You should try to limit the number of
aliases you have to a reasonable number (10 or 15). Having too many aliases causes
delays and makes the system seem sluggish when you execute commands from within an
editor or other programs.
Redirecting Input and Output
In addition to the standard output, commands also have a standard error output that is
normally directed to the terminal even when the standard output is redirected to a file
or a pipe. It is occasionally useful to redirect the standard error output along with the
standard output. For instance, if you want to redirect the output of a long-running
command into a file and wish to have a record of any error message it produces, you can
type
command >& file
The ">&" here tells the C shell to route both the standard error output and the standard
output into file. Similarly, you can give a command of the form
command I& lpr
to route both standard output and standard error output through the pipe to the line
printer.
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