Embedding Commands


Suppose you create a script that will automatically run when you log in each day. The script might, for example, print "Greetings!" onscreen and possibly deliver a cle(a)ver message: "Say, you're looking sharp today!" You could easily do this with the information you've learned so far in this chapter.

What would be handy here would be to add a line to the script that tells Unix to do all those things plus name the most recently used filefor those of you who need a reminder about what you were last working on. You could just use an ls command, but that would only list the filenames and not integrate the information with the rest of your morning greeting. Instead, a better (and more attractive) idea would be to bundle a couple of commands and use them with echo (Figure 10.4) to embed the information right into the greeting.

Figure 10.4. Embedding commands just requires an additional couple of lines in the script.


To Embed a Command:

1.

vi myscript

To begin, open myscript or another script in your favorite editor. Your script might look like Figure 10.4, with the greeting onscreen.

Using Clever Dates

You can use the date command to deliver any date with any format. In general, use date +"Today is %A", but you can use any or all of the following bits:

  • %d includes the two-digit day of month.

  • %y includes the two-digit year.

  • %Y includes the four-digit year.

  • %m includes the numeric month.

  • %b includes an abbreviated month.

  • %B includes the full month name.

  • %a includes the abbreviated day of the week.

  • %A includes the full day of the week.

  • %R includes the time in hours and minutes.

  • %D includes the date in month/date/year format.

Check the man pages for the remaining several dozen options.


2.

echo "You were most recently working" on `ls -1Fc ~/ | head -1`."

Type echo followed by the descriptive text you want to see. Then embed the ls command (`ls -1Fc ~/ | head -1`) within the descriptive text. Note that the embedded code begins and ends with ` before . (dot).

The embedded command here lists just the most recently changed file or directory in the home directory. 1 provides for one entry per line, F formats the directory names with a / so we can tell whether we're working in a subdirectory or on a file, and c sorts by the modification date. We then pipe the output to head -1, which displays the top line of the file.

3.

Save your script and exit the editor, and then try it out, as in Code Listing 10.3.

Tips

  • You can embed dates into scripts, too. Try echo -e "Today is `date +%A`" if you work so much that you forget what the day of the week is. See the sidebar Using Clever Dates for more date details.

  • When you embed commands that are directory-dependentsuch as ls or find be sure to specify the complete path. If you don't, you'll get paths relative to where the script is rather than relative to where you're running the script from.

  • Embedded commands are useful in many ways. You can use them anytime that you want to have one program act based on the output of another program, just as echo displays something based on the output of a program.


Code Listing 10.3. The results of embedded commands can be impressive.

[ejr@hobbes scripting]$ myscript Greetings!  Say, you're looking mighty sharp today! You were most recently working on figlet. [ejr@hobbes scripting]$ 




Unix(c) Visual Quickstart Guide
UNIX, Third Edition
ISBN: 0321442458
EAN: 2147483647
Year: 2006
Pages: 251

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