Chapter Summary


Like the Bourne Again Shell, the TC Shell is both a command interpreter and a programming language. The TC Shell, which is based on the C Shell that was developed at the University of California at Berkeley, includes popular features such as history, alias, and job control.

You may prefer to use tcsh as a command interpreter, especially if you are familiar with the C Shell. You can use chsh to change your login shell to tcsh. However, running tcsh as your interactive shell does not cause tcsh to run shell scripts; they will continue to be run by bash unless you explicitly specify another shell on the first line of the script or specify the script name as an argument to tcsh. Specifying the shell on the first line of a shell script ensures the behavior you expect.

If you are familiar with bash, you will notice some differences between the two shells. For instance, the syntax you use to assign a value to a variable differs and tcsh allows SPACEs around the equal sign. Both numeric and nonnumeric variables are created and given values using the set builtin. The @ builtin can evaluate numeric expressions for assignment to numeric variables.

setenv

Because there is no export builtin in tcsh, you must use the setenv builtin to create an environment (global) variable. You can also assign a value to the variable with the setenv command. The command unset removes both local and environment variables, whereas the command unsetenv removes only environment variables.

Aliases

The syntax of the tcsh alias builtin is slightly different from that of alias in bash. Unlike bash, the tcsh aliases permit you to substitute command line arguments using the history mechanism syntax.

Most other tcsh features, such as history, word completion, and command line editing, closely resemble their bash counterparts. The syntax of the tcsh control structures is slightly different but provides functionality equivalent to that found in bash.

Globbing

The term globbing, a carryover from the original Bourne Shell, refers to the matching of strings containing special characters (such as * and ?) to filenames. If tcsh is unable to generate a list of filenames matching a globbing pattern, it displays an error message. This behavior contrasts with that of bash, which simply leaves the pattern alone.

Standard input and standard output can be redirected in tcsh, but there is no straightforward way to redirect them independently. Doing so requires the creation of a subshell that redirects standard output to a file while making standard error available to the parent process.




A Practical Guide to UNIX[r] for Mac OS[r] X Users
A Practical Guide to UNIX for Mac OS X Users
ISBN: 0131863339
EAN: 2147483647
Year: 2005
Pages: 234

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