Using csh & tcsh

Using {} To Generate Arguments

Filename patterns can be used only to refer to existing files. If you need to specify names, regardless of whether or not the files exist (usually to create new files or give new names to existing ones), use the shell's {} construct.

Suppose that you want to create a set of new directories with names Project1 through Project5. You can't use a pattern like Project[1–5], because that pattern works only for existing names, as shown below:

% mkdir Project[1-5]
mkdir: No match.

You could type out every name:

% mkdir Project1 Project2 Project3 Project4 Project5

But that's tedious. It's much easier to use {} to generate arguments:

% mkdir Project{1,2,3,4,5}

The shell looks at the comma-separated strings between the braces and creates one argument for each string.

You can use {} to mix references to existing and nonexisting files. The following command renames chapter8 to chapter9, even if chapter9 doesn't exist:

% mv chapter{8,9}

To rename the file to its original name, do the following:

% mv chapter{9,8}

Any or all of the strings within {} can be empty. Therefore, the following pairs of commands are equivalent:

• Compare document.old and document for differences:

  % diff document.old document
  % diff document{.old,}

• Make a backup copy of program.c named progam.c.bak:

  % cp program.c program.c.bak
  % cp program.c{,.bak}

• Encode a file utilities-3.04.tar.Z into junk:

  % uuencode utilities-3.04.tar.Z utilities-3.04.tar.Z > junk
  % uuencode utilities-3.04.tar.Z{,} > junk

{} might not be ...