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Using csh & tcsh by Paul DuBois

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Chapter 12. Using Commands To Generate Arguments

In This chapter:

  • Command Substitution

  • Repeating Substituted Commands

  • Deferred Command Substitution

  • When To Avoid Command Substitution

This chapter describes how to use one command to supply arguments for another. This valuable technique can be used by itself or in conjunction with other argument generators, such as pattern-matching operators.

Command Substitution

The shell helps you issue commands by providing shorthand methods for specifying command arguments. The most common technique is to use filename patterns to generate a list of files, so that you don’t have to type each filename explicitly. For example, to edit all the C source files in your current directory, you could select them easily with the following pattern:

% vi *.c

But filename patterns have certain limitations. You cannot use them to select filenames based on file content, to search through directory hierarchies, or to select files based on criteria such as age, ownership, size, type, etc.

For such tasks, other file selection strategies may be used. For example, it may be relatively easy to generate the appropriate filenames by running a command. Suppose you want to identify the files that contain the string “gaboon,” and then edit them to say “viper” instead. A filename pattern by itself will not tell you which files contain “gaboon,” but a command consisting of grep in conjunction with a pattern works quite well, as shown below:

% grep -li gaboon *

The command shown above ...

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