What does dnl stand for in the m4 macro

The ifdef macro permits three arguments. If the first argument is defined, the value of ifdef is the second argument. If the first argument is not defined, the value of ifdef is the third argument:. If there is no third argument, the value of ifdef is null. So far you have been given information about the simplest form of macro processing, that is, replacing one string with another fixed string. Macros can also be defined so that different invocations have different results.

So the macro bump , defined as. As noted, arguments that are not supplied are replaced by null strings, so a macro can be defined that concatenates its arguments:. That is, cat x, y, z is equivalent to xyz. Leading unquoted blanks, tabs, or newlines that occur during argument collection are discarded. All other white space is retained, so.

Arguments are separated by commas. A comma "protected" by parentheses does not terminate an argument. The following example has two arguments, a and b,c. You can specify a comma or parenthesis as an argument by quoting it:. The listed arguments are separated by commas.

That is,. The built-in shift returns all but its first argument. The other arguments are quoted and returned to the input with commas between. The simplest case. So, to handle the common programming situation in which a variable is to be defined as "one more than N," you would use:. The more general mechanism for arithmetic is a built-in macro called eval , which is capable of arbitrary arithmetic on integers.

Its operators, in decreasing order of precedence, are. Parentheses may be used to group operations where needed. All the operands of an expression given to eval must ultimately be numeric. The precision in eval is 32 bits. A new file can be included in the input at any time with the built-in macro include :.

The value of include its replacement text is the contents of the file. If needed, the contents can be captured in definitions, and so on.

A fatal error occurs if the file named in include cannot be accessed. To get some control over this situation, the alternate form sinclude "silent include" can be used. This built-in says nothing and continues if the file named cannot be accessed. If the built-in macro divert n is used, all subsequent output is appended to a temporary file referred to as n. Diverting to this file is stopped by the divert or divert 0 macros, which resume the normal output process. Diverted text is normally placed at the end of processing in numerical order.

Diversions can be brought back at any time by appending the new diversion to the current diversion. Output diverted to a stream other than 0 through 9 is discarded. The built-in undivert brings back all diversions in numerical order; undivert with arguments brings back the selected diversions in the order given. Undiverting discards the diverted text as does diverting into a diversion whose number is not between 0 and 9, inclusive. The value of undivert is not the diverted text.

Furthermore, the diverted material is not rescanned for macros. The built-in divnum returns the number of the currently active diversion. The current output stream is 0 during normal processing. Any program can be run by using the syscmd built-in. The following example invokes the operating system date command. Normally, syscmd would be used to create a file for a subsequent include. To make it easy to name files uniquely, the built-in maketemp replaces a string of XXXXX in the argument with the process ID of the current process.

Arbitrary conditional testing is performed with the built-in ifelse. In its simplest form. If a and b are identical, ifelse returns the string c. Otherwise, string d is returned. Thus, a macro called compare can be defined as one that compares two strings and returns yes or no , if they are the same or different:. Notice the quotes, which prevent evaluation of ifelse from occurring too early. If the final argument is omitted, the result is null, so. In the input. Otherwise, if d is the same as e , the result is f.

Otherwise, the result is g. The len macro returns the length of the string number of characters in its argument. If n is omitted, the rest of the string is returned. When you input the following example:. What is the worlds largest wan. What is a network server. Computers 21 cards. What is an decimal numbering system. What are the advantages of computer aided design and computer aided manifaturing.

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What is application software. Q: What does dnl stand for in the m4 macro language What are dnl commands used for? Write your answer Related questions. Why getchar is used in c? What is the Kabye language in Lome Togo stand for?

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Do dogs respond better to Japanese or English commands? How do you do a macron on Microsoft word? What is the select element? Example It runs an executable named lt-m4. This is why the signature in the error message is "wrong". We have a serious problem, for our ultimate goal is to write a test suite shipped with GNU M4. One possibility consists in adjusting the expected error messages to using lt-m4. This would prevent us from using our test suite on any other m4. In addition it clashes with an important motto: the test suite is a user, see Look for Realism.

Another is having the test suite be robust enough to work with different signatures, i. What a hassle! For the time being, let us just imagine we didn't read Designing a Test Suite.