M4 assualt rifle. Use arrow keys. Royalty Free License. Read more about enhanced license tiers , or contact us at enterprise turbosquid. Your Cart View Full Cart. Open Support Ticket.
Close the Cart. Invalid Payment Information. Please complete the required fields. For help: Chat or Contact Support. Billing Address. Telephone Number. Account Supervisor:. Supervisor Email:. Supervisor Telephone:. Current Credit Balance:. Available Credit:. Default Payment Method:. If you want echoing block comments , you can also change the closing delimiter, e. For a comment that should not be echoed to the output, use dnl : this macro not only prevents the following newline from being output as we saw above , it also discards everything up to the newline.
Non-echoing block comments : multiline comments that are not echoed to the output can be written like this. This is a hack which takes advantage of the fact that the ifelse macro described below has no effect if it is passed only one argument. Some versions of m4 may therefore issue a warning about insufficient arguments; GNU m4 doesn't.
The definition being tested may be empty, e. If they match, the macro expands to string c; if not, string d. In other words, it's shorthand for. M4 normally treats numbers as strings. However, the eval macro allows access to integer arithmetic ; expressions can include these operators in order of precedence. The above table is for GNU m4; unfortunately, the operators and precedence are version-dependent. For maximum compatibility, make liberal use of parentheses to enforce precedence.
Should you need it, octal , hexadecimal and indeed arbitrary radix arithmetic are available. It's also possible to specify the width of eval 's output. See the m4 info pages for details on these. There are also incr and decr builtins as shortcuts which expand to the argument plus or minus one, e. Beware of silent integer overflow , e. GNU m4 includes some additional string macros: regexp , to search for a regular expression in a string, and patsubst , to do find and replace.
Unfortunately, m4's usual approach of rescanning the expansion of a macro can be a problem with macros that operate on strings:. This is not normally the desired behaviour and is arguably a design bug in m4: the builtins should at least provide some way to allow us to prevent the extracted or transformec substring from being expanded. A workaround is suggested below. GNU m4 has no fixed limit on the number of arguments. Arguments default to the empty string, e. Going in at the deep end, here is a reimplementation of the len builtin replacing it as a recursive macro.
Where necessary, this immediate expansion can be prevented by breaking up the reference with inside quotes , e. Note in the following example that empty parentheses are treated as delimiting a single argument : an empty string:. A common requirement is to process a list of arguments where we don't know in advance how long the list will be. Here, the shift macro comes in useful — it expands to the same list of arguments with the first one removed:.
In particular, suppose we want to avoid accidentally redefining a macro used somewhere else. Unfortunately, this isn't entirely satisfactory — and it won't work at all in a recursive macro.
A better approach is described in the next section. For each macro, m4 actually creates a stack of definitions — the current definition is just the one on top of the stack. It's possible to temporarily redefine a macro by using pushdef to add a definition to the top of the stack and, later, popdef to destroy only the topmost definition:.
If the macro hasn't yet been defined then pushdef is equivalent to define. As with undefine , it is not an error to popdef a macro which isn't currently defined; it simply has no effect.
Actually, we can say that m4 does expand the macro — but that it expands only to the same literal string. Unfortunately, some macros do not require arguments and so m4 has no way of knowing whether a word corresponding to a macro name is intended to be a macro call or just accidentally present in the text being processed. Also, other versions of m4, and older versions of GNU m4, may expand macro names which are not followed by arguments even where GNU m4 does not:.
However if you are not fully in control of the text being passed to m4 this can be troublesome. Potentially more problematic are dictionary words that are recognized as macros even without arguments:.
An alternative to quoting macro names is to change all m4's macro names so that they won't clash with anything. On the basis that unnecessary changes to a language are generally undesirable, I suggest not using -P option if you can comfortably avoid it.
However, if you are writing a set of m4 macros that may be included by others as a module, do add some kind of prefix to your own macros to reduce the possibility of clashes. Although m4 provides no builtins for iteration, it is not difficult to create macros which use recursion to do this.
Various implementations can be found on the web. Note the use of pushdef and popdef to prevent loop variables clobbering any existing variable; in the nested for loop, this causes the second x to hide shadow the first one during execution of the inner loop.
To discard output — in particular, to prevent newlines in a set of definitions being output — use divert :. Unlike the contents of a comment, the definitions and any other macros are still processed by m4; divert -1 merely causes m4 to do this silently, without sending anything to the output. The last line above, with its dnl to prevent the following newline being echoed, could also have been written:. Standard m4 has 9 buffers Note that undivert is the same as undivert 0 and has no effect: diversion 0 is stdout which is effectively an empty buffer.
The contents of the buffer are not interpreted when undivert is run, they are simply output as raw text, e. There is an implicit divert and undivert when m4 reaches the end of the input, i. If you want to avoid this for any reason, you can of course discard the contents of the buffers by putting the following line at the end of your input. GNU m4 allows for an include file search path.
To specify directories to be searched for include files use the -I option on the command line, e. To include a file uninterpreted, GNU m4 allows undivert to be passed a filename argument.
If inc. But it was like Prolog, after one page of code you lost all control and comprehension. And enthusiasm. I'm interested in learning about prolog. Where can I learn about the problems with it? The problem with prolog is that it is incomplete.
If the unix CLI isn't going to slowly rot away, it needs to pick up improved versions of tools like this and start getting them into wide distribution. I agree, something better has to be possible. Maybe it could begin with some simplifying assumptions to reduce the complexity of quoting.
I used it 25 years ago! I'm sure the kids are doing this more elegantly today, but it sure saved us a lot of time! Seconding other comments - assuming you can use Python, use jinja templates, slap on a twenty-line Python wrapper script to read your data and then apply it to the templates, and then you've saved yourself of days of headache. I'd really like to see what the m4 equivalent of the original Bourne shell code or the APL Incunabulum would be. While Turing complete, and not merely in a highly technical, obtuse way e.
I'm sure you can make it work using extensions like GNU Make's esyscmd and some preprocessing, but it would be ugly and even more impenetrable than typical recursive string interpolation code. To reimplement complex software you'd probably end up implementing a tiny VM in m4 and then targeting the VM. Though, I suppose m4 is far more accommodating in this regard than, e. IOW, m4 is really only suited for fairly straight-forward static input-output transformations, such as common templating tasks.
These transformations can themselves become quite complex and even convenient to implement put your functional programming hat on , but once you stray from recursive string interpolation on lists of simple tokens sourced from statically defined input the ergonomics break down immediately. How large does that body have to be?
Autoconf consists of M4 macros, so all software that uses Autoconf uses m4. During my CS degree in I wrote a simple programming language that macro expanded using m4 into lambda calculus that was then converted to SK combinators for evaluation.
I too at one point suffered from a similar affinity towards 'minimalism'. Nothing good came out of it. With things like go get and nix you can be more or less independent of package managers or even OS to some extent.
Koshkin 5 months ago prev next [—]. This can be used with any programming language that has quoted string literals. It's a line from the musical Hamilton. Just no. As a curiosity for small projects it's okay. Seeing what's out there and extending one's view of the programming landscape is great. But if you use it in a professional environment for heaven's sake please think of the maintainers that come after you and just don't use it.
I TA'd a couple assembly courses that used m4 as a preprocessor. Slight syntax errors result in some gnarly error messages, and students really struggled with it. Heck, I struggled with it sometimes. You call it "unwieldy", other people call it "available everywhere and battle-tested".
That we tend to implement slightly more aesthetic alternatives to existing, proven software instead of reusing stuff and building for reuse , is probably the main reason why complex software is so bad unstable, difficult to get accustomed with and maintain nowadays.
A musket is also battle-tested, but it was replaced because it is slow, hard to operate, heavy, and in the end if you tried to continue using one, you lost. M4 is similar. It's just a macro processor. If you try to make it work on a problem that requires more, it will backfire in uncomfortable ways. Ah, the joy of cherry-picked analogies.
Let's replace the musket with an AK, how does it look now? Yes, M4 is a macro processor. A pretty decent one that is well-known and will not surprise you with incompatible changes or newly introduced bugs. Nobody suggested using it for more. AK had been superseded by AKM after less than 10 years in service. AKM was, in turn, superseded by AK And AK has been superseded by AK The last transition, in particular, was heavily motivated by ergonomics and difficulty of adapting the original to typical modern circumstances of use.
So, I'd say the analogy still holds up pretty well. I'd rather have someone learn to use M4 when needed than have "some Python" replace M4 in an important project. But that's just me, other people like building sand castles. You gotta strive to use a right tool for the job, always. Using m4 as a template processor for HTML isn't it. Zababa 5 months ago root parent prev next [—].
I don't think it's proven if most of the people that had to work with it complain about the complexity of doing a simple loop. I also don't think it's built for reuse, considering so few people actually use it. If anything, hard to use software like m4 is exactly what pushes everyone to think "I can do better! What font is this blog written with? None of us will know what font you are seeing on your system. Right click and Inspect the element and you can see that it's using Fira Mono.
Most of these classic unix tools aren't particularly good examples of what they do, they're just old enough to have become established. I believe M4 was originally created to simplify the sendmail config file and then eventually pulled out into its own program? Rather like this writer, I felt the need to make my blog entries markdown with minimum header and footer surrounding them.
So I found a one-liner script that renders markdown in the browser. LukeShu 5 months ago parent next [—]. The 7th edition manual[1] says m4 was based on m3, which was based on the Software Tools macroprocessor. Never occurred to me that these two are related. A ton of people argue for them, but when you ask people to re-design them starting from scratch today, few people arrive to the design of the Bourne shell, for example.
SkyMarshal 5 months ago parent prev next [—]. Any chance you can link that script? Care to share the one-liner?
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