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7.2. Executing UNIX Commands

You can display or read in the results of any UNIX command while you are editing in vi. An exclamation mark (!) tells ex to create a shell and to regard what follows as a UNIX command:

:!command

So if you are editing and you want to check the time or date without exiting vi, you can enter:

:!date

The time and date will appear on your screen; press RETURN to continue editing at the same place in your file.

If you want to give several UNIX commands in a row without returning to vi editing in between, you can create a shell with the ex command:

:sh

When you want to exit the shell and return to vi, press CTRL-D.

You can combine :read with a call to UNIX, to read the results of a UNIX command into your file. As a very simple example:

:r !date

will read in the system's date information into the text of your file. By preceding the :r command with a line address, you can read the result of the command in at any desired point in your file. By default, it will appear after the current line.

Suppose you are editing a file and want to read in four phone numbers from a file called phone, but in alphabetical order. phone reads:

Willing, Sue  333-4444
  Walsh, Linda  555-6666
  Quercia, Valerie  777-8888
  Dougherty, Nancy  999-0000

The command:

:r !sort phone

reads in the contents of phone after they have been passed through the sort filter:

Dougherty, Nancy  999-0000
  Quercia, Valerie  777-8888
  Walsh, Linda  555-6666
  Willing, Sue  333-4444

Suppose you are editing a file and want to insert text from another file in the directory, but you can't remember the new file's name. You could perform this task the long way: exit your file, give the ls command, note the correct filename, reenter your file, and search for your place.

Or you could do the task in fewer steps:

Keystrokes Results
:!ls Figure

Display a list of files in the current directory. Note the correct filename. Press RETURN to continue editing.

:r newfile Figure

Read in the new file.

7.2.1. Filtering Text Through a Command

You can also send a block of text as standard input to a UNIX command. The output from this command replaces the block of text in the buffer. You can filter text through a command from either ex or vi. The main difference between the two methods is that you indicate the block of text with line addresses in ex and with text objects (movement commands) in vi.

7.2.1.2. Filtering text with vi

In vi, text is filtered through a UNIX command by typing an exclamation mark followed by any of vi's movement keystrokes that indicate a block of text, and then by the UNIX command line to be executed. For example:

!)command

will pass the next sentence through command.

There are a few unusual features about how vi acts when you use this feature:

As another example, assume you have a portion of text in a file that you want to change from lowercase to uppercase letters. You could process that portion with the tr command to change the case. In this example, the second sentence is the block of text that will be filtered through the command.

Figure 7.2.1.2
Keystrokes Results
!) Figure

An exclamation mark appears on the last line to prompt you for the UNIX command. The ) indicates that a sentence is the unit of text to be filtered.

tr '[a-z]' '[A-Z]' Figure

Enter the UNIX command and press RETURN. The input is replaced by the output.

To repeat the previous command, the syntax is:

! object !

It is sometimes useful to send sections of a coded document to nroff to be replaced by formatted output. (Or when editing electronic mail, you might use the fmt program to "beautify" your text before sending the message.) Remember that the "original" input is replaced by the output. Fortunately, if there is a mistake, such as an error message being sent instead of the expected output, you can undo the command and restore the lines.



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