Find sources: — · · · · March 2010 In , a unary operation is an with only one , i. After the operator, it expects to see a boolean expression. If this question can be reworded to fit the rules in the , please. I had a quick look at the manpage but did not find anything that explains this behavior. Introduction to Linux - A Hands on Guide This guide was created as an overview of the Linux Operating System, geared toward new users as an exploration tour and getting started guide, with exercises at the end of each chapter. When that fails, it gives the appropriate syntax error. About how to start this script automatically on login, you can read or To fix this specific problem There are other issues with your script presumably dealt with in Byte Commander's answer, but for those coming in from Google, to fix this specific problem, always surround variables with double quotes.
This is in contrast to , which use two operands. The unary minus is done first, so it applies only to the twelve. I am pasting the actual content of the script below. Provide details and share your research! For example -12 + 3 means add 3 to negative 12 resulting in -9. A binary operator has two arguments. . Registration is quick, simple and absolutely free.
Expressions may be combined using the following operators, listed in decreasing order of precedence. For more advanced trainees it can be a desktop reference, and a collection of the base knowledge needed to proceed with system and network administration. Are you new to LinuxQuestions. Since '-1' cannot be evaluated as a boolean value, it looks for a unary operator. You don't need to do so again.
Unless the echo command fails, you're setting notok to 0 here in every case. By contrast, binary operations, such as addition, require two different terms to compute a result. But it generates an error as :. Since '-1' cannot be evaluated as a boolean value, it looks for a unary operator. By joining our community you will have the ability to post topics, receive our newsletter, use the advanced search, subscribe to threads and access many other special features. A boolean expression could be either a boolean value, or a more complex expression beginning with a unary operator.
According to the man-page it determines that the first argument and the second argument must be operands and thus treated as such. I'm not sure what you are trying to do. Having a problem logging in? Perhaps you are trying to check if the value is non-zero? Visit the following links: If you have any problems with the registration process or your account login, please. . That is because - is used for two purposes.
. This book contains many real life examples derived from the author's experience as a Linux system and network administrator, trainer and consultant. Apparently, this is not the case. Always quote your variables when performing comparisons if there is the slightest chance that one of them may be empty, e. If you look in the you will see that the character - is listed twice. I am looping through different values of h and k and sums is calculated from them. For example, in the case of the , a horizontal bar extending the square root sign over the argument can indicate the extent of the argument.
Thanks for contributing an answer to Super User! Note that registered members see fewer ads, and ContentLink is completely disabled once you log in. . Other notations exist as well. . . In other contexts, - is the subtraction operator.
Perhaps you are trying to check if the value is non-zero? Unsourced material may be challenged and removed. If you don't want to rewrite your script, just initialize the notok variable with any number different from 0 before your main code. Therefore it should have determined that '-a' is a binary operator and treat '-1' as operand. They hope these examples will help you to get a better understanding of the Linux system and that you feel encouraged to try out things on your own. This is even sillier when you realize that you've already checked the exit status. It is more nicely formatted, fixes some errors we had in the original script, correctly quotes the variables in the if tests and uses actually working commands to get and set the nvidia settings value, as we found out the ones in the original script did not do anything on your system. This is because it is possible to provide only one term as input for these functions and retrieve a result.
. Explanation A unary operator only has one argument. If the first argument is! Nothing wrong with it in this specific case, however. A boolean expression could be either a boolean value, or a more complex expression beginning with a unary operator. What if one of those was blank, though? I'm not sure what you are trying to do.
Or is my logic failing me? Your variables can be blank, causing just this problem. Addition and subtraction have low precedence. Can any one help me in resolving the issue? Otherwise, the expression is parsed and evaluated according to precedence using the rules listed above. How do you solve it? The script expression has a boolean operator. . Those are missing one of the arguments, so the shell gets to thinking you meant to use an operator that only has one argument, a unary operator. The shell is treated like a black box by many, but it operates with very few and very simple rules - once you are aware of what those rules are one of them being how variables work in the shell, as explained above the shell will have no more secrets for you.