dr_unix% echo "I am on the $ith page now." So far so good, but consider the following: dr_unix% echo "I gave the papers to $spy in Munich."Īnd if you want to destroy a variable, just use unset: I just wanted to preempt a lot of e-mails.īy and large, variables are easy to embed within command lines. Still, we're stuck with it, and to be honest, you'll get used to it very quickly. However, you are not alone, because Larry Wall asked this, too, when he was creating Perl. csh and tcsh do this the same way that the first shell, the Bourne Shell ( sh), does it, so I think this is a case of "Well, everyone/shell is doing it." I'm hanged if I know why Stephen Bourne did it like this in the first place, though. Unix Geek?" And the answer is: I don't know. Now this bit of inconsistency may cause you to ask "So why the heck didn't they just let you say '$i=9' when you set the variable? Huh, Mr. The shell needs to differentiate between the character 'i' and the value of the variable 'i'. Now, you might think that, to print out the value of the variable you could just tell the shell to print it:īut you see the problem. This can be useful in a script in certain contrived circumstances, or in certain reserved or 'built-in' variables that tcsh uses: You could also define the variable without giving it a value. This creates the variable 'i', if it does not exist yet, and assigns the value of '9' to that variable. In tcsh and csh, a variable's value is set simply by typing (And besides, we want to be able to automate things with shell scripts some day, right?) While not as useful on the command line as in a shell script, shell variables are too useful to be ignored. Shell variables are those known only to the particular shell you are running, be it a shell script or a command line window. There are two types of variables in tcsh: shell variables and environment variables. Variables in tcsh are a rather large topic. They allow you to store and manipulate data, of course but in doing so, they make possible many convenient things, like error checking or setting default behavior of a program (or command line environment). Variables are a very basic part of any computer language. If you have any questions about what you read here, check out the earlier columns, write back in the comments below, or join us in the Hardcore X! forum.
#Set command line to use java 8 mac os x mac os x
This series is designed to help you learn more about the Mac OS X command line. Jonathon Swift, "Critical Essays upon the Faculties of the Mind"" There is nothing in this world constant, but inconstancy. The Mac Observer Express Daily Newsletter