UNIX for Dummies Questions & Answers

context:

while reading tutorial on the read command, one of the first examples, demonstrating its use, follows as such:

$ x=abc ; printf "x is now '%s'. Enter new value: " $x ; read x

generating this output:

x is now 'abc'. Enter new value:

first, what does %s represent? I know in this context that it will obviously reflect the value of the just-defined variable x ('abc') but outside of this context??? And if the author wanted to display this variable, why did he use %s instead of $x???

Also for bonus stickers, explain the reason for spaces around semi-colons. I've seen it before, but I know semi-colons to inject end-of-line or carriage-return signal so I know them to work without the preceding or ensuing space?? Is my grasp accurate/correct? Maybe distinguishing why spacing vs not spacing and its effects would explain to me.

many thanks in advance, party people of the internet!

Hi,
The printf statement takes arguments, and in this case the first argument is a string (between quotes and separate from the other arguments) containing formatting information as well. The first "placeholder" is in this case %s but it could be %d or some other description. The first %s says to take the first of the following arguments (the first one after the string) and print it as a string. Using %d would print it as a number. This is a very simple example. Most people would use $x in the string instead in this case. But the power of printf is that You can FORMAT the output, ie padding with spaces, padding numbers with zero's, use a fixed number of decimal places, etc. Space or not around semicolon is irrelevant as far as I know.

/Lakris

Lakris,

Thanks for the explanation. I had done some reading and I understood what printf was intended to do, but I didn't realize that the $x after the quotes was intended to be the input for the %s, as you put it--A PLACEHOLDER!!

Now it all makes sense, thank you very much!! I cannot explain how thankful I am. Look forward to more posts from you.

--
Your friendly neighborhood programmar MARS!

You're welcome!

/Lakris