Variables defined with `:=` in [GNU make][1] are expanded when they are defined rather than when they are used.

  [1]: http://www.gnu.org/software/make/manual/make.html#Flavors

Maybe I&#39;m just blind, but I don&#39;t see an explicit [set command][1] in Redis for emptying an existing set (without emptying the entire database). For the time being, I&#39;m doing a set difference on the set with itself and storing it back into itself:

    redis&gt; SMEMBERS metasyn
    1) &quot;foo&quot;
    2) &quot;bar&quot;
    redis&gt; SDIFFSTORE metasyn metasyn metasyn
    (integer) 0
    redis&gt; SMEMBERS metasyn
    (empty list or set)

But that looks a little silly... is there a better way to do this?


  [1]: http://redis.io/commands#set

Empty/delete a set in Redis?

Okay, so I&#39;m trying to make a full text search in multiple columns, something simple like this:

    SELECT * FROM pages WHERE MATCH(head, body) AGAINST(&#39;some words&#39; IN BOOLEAN MODE)

Now i want to order by relevance, (how many of the words are found?) which I have been able to do with something like this:

    SELECT * , MATCH (head, body) AGAINST (&#39;some words&#39; IN BOOLEAN MODE) AS relevance 
    FROM pages
    WHERE MATCH (head, body) AGAINST (&#39;some words&#39; IN BOOLEAN MODE)
    ORDER BY relevance

Now here comes the part where I get lost, I want to prioritize the relevance in the `head` column.

I guess I could make two relevance columns, one for `head` and one for `body`, but at that point I&#39;d be doing somewhat the same search in the table three times, and for what i&#39;m making this function, performance is important, since the query will both be joined and matched against other tables.

**So, my main question is**, is there a faster way to search for relevance and prioritize certain columns? (And as a bonus possibly even making relevance count number of times the words occur in the columns?)

Any suggestions or advice would be great.

**Note:** I will be running this on a LAMP-server. (WAMP in local testing)

MySQL match() against() - order by relevance and column?

&gt; **Possible Duplicate:**  
&gt; https://stackoverflow.com/questions/448910/makefile-variable-assignment

&lt;!-- End of automatically inserted text --&gt;

I only know very basic `makefile` syntax, and was reading through another project&#39;s `makefile` and came across `:=` for macro declaration. Why would they use that?

In other words, is there any difference between

    MYMACRO = hi i&#39;m a macro

and

    MYMACRO := hi i&#39;m a macro
?

:= vs = in make macros

> Possible Duplicate: 
> <a href="https://stackoverflow.com/questions/448910/makefile-variable-assignment" target="_blank" rel="noopener noreferrer">https://stackoverflow.com/questions/448910/makefile-variable-assignment</a>

I only know very basic <code>makefile</code> syntax, and was reading through another project's <code>makefile</code> and came across <code>:=</code> for macro declaration. Why would they use that?
In other words, is there any difference between
<pre><code class="hljs language-css">MYMACRO = hi i'm a macro
</code></pre>
and
<pre><code class="hljs language-rust">MYMACRO := hi i'm a macro
</code></pre>
?

i use git as a version tracker for my c++ project. 

sometimes i need to repeat a calculation and i would like to know which version of the program i used.

what would be a good way to put a # of the commit into the main executable? in other words. i&#39;d like the program to tell me the # of the current commit in an introductory message as i run the program.

one way i can think of is to make the c++ program lunch &quot;git log&quot; from shell and extract the commit # but i&#39;m not sure how to do it during make.

(I use linux)

how to include git commit-number into a c++ executable?

I&#39;m developing cross-platform c++ project. The original idea is to work with msvc2010 and later compile for other systems with the help of CMake and Hudson.
It doesn&#39;t seem to be convenient manually change CMake files after changes in studio settings.

So, what’s the easiest way: to write parser for vcxproj and vcxproj.filters, or there is another good solution?

How to support both vcxproj to cmake on a project?

How can I create a variable on-the-fly from makefile, the value of which would be the entire contents of another data file.

Create a variable in a makefile by reading contents of another file

Just upgraded my computer to Mac OS X Lion and went to terminal and typed &quot;make&quot; but it says:
-bash: make: command not found

Where did the &quot;make&quot; command go?



Where can I find &quot;make&quot; program for Mac OS X Lion?

A few months ago, I came up with the following generic `Makefile` for school assignments:


    # ------------------------------------------------
    # Generic Makefile
    #
    # Author: yanick.rochon@gmail.com
    # Date  : 2010-11-05
    #
    # Changelog :
    #   0.01 - first version
    # ------------------------------------------------
    
    # project name (generate executable with this name)
    TARGET   = projectname
    
    CC       = gcc -std=c99 -c
    # compiling flags here
    CFLAGS   = -Wall -I.
    
    LINKER   = gcc -o
    # linking flags here
    LFLAGS   = -Wall
    
    SOURCES  := $(wildcard *.c)
    INCLUDES := $(wildcard *.h)
    OBJECTS  := $(SOURCES:.c=*.o)
    rm       = rm -f
    
    $(TARGET): obj
    	@$(LINKER) $(TARGET) $(LFLAGS) $(OBJECTS)
    	@echo &quot;Linking complete!&quot;
    
    obj: $(SOURCES) $(INCLUDES)
    	@$(CC) $(CFLAGS) $(SOURCES)
    	@echo &quot;Compilation complete!&quot;
    	
    clean:
    	@$(rm) $(TARGET) $(OBJECTS)
    	@echo &quot;Cleanup complete!&quot;

This will basically compile every `.c` and `.h` file to generate `.o` files and the executable `projectname` all in the same folder.

Now, I&#39;d like to push this a little. **How can I write a Makefile to compile a C project with the following directory structure?**

     ./
     ./Makefile
     ./src/*.c;*.h
     ./obj/*.o
     ./bin/&lt;executable&gt;

In other words, I&#39;d like to have a Makefile that compiles C sources from `./src/` into `./obj/` and then link everything to create the executable in `./bin/`.

I&#39;ve tried to read different Makefiles, but I simply can&#39;t make them work for the project structure above; instead, the project fails to compile with all sorts of errors. Sure, I could use full blown IDE (Monodevelop, Anjuta, etc.), but I honestly prefer to stick with gEdit and the good ol&#39; terminal.

Is there a guru who can give me a working solution, or clear information about how this can be done? Thank you!

** **UPDATE (v4)** **

The final solution :


    # ------------------------------------------------
    # Generic Makefile
    #
    # Author: yanick.rochon@gmail.com
    # Date  : 2011-08-10
    #
    # Changelog :
    #   2010-11-05 - first version
    #   2011-08-10 - added structure : sources, objects, binaries
    #                thanks to http://stackoverflow.com/users/128940/beta
    #   2017-04-24 - changed order of linker params
    # ------------------------------------------------
    
    # project name (generate executable with this name)
    TARGET   = projectname
    
    CC       = gcc
    # compiling flags here
    CFLAGS   = -std=c99 -Wall -I.
    
    LINKER   = gcc
    # linking flags here
    LFLAGS   = -Wall -I. -lm
    
    # change these to proper directories where each file should be
    SRCDIR   = src
    OBJDIR   = obj
    BINDIR   = bin
    
    SOURCES  := $(wildcard $(SRCDIR)/*.c)
    INCLUDES := $(wildcard $(SRCDIR)/*.h)
    OBJECTS  := $(SOURCES:$(SRCDIR)/%.c=$(OBJDIR)/%.o)
    rm       = rm -f
    
    
    $(BINDIR)/$(TARGET): $(OBJECTS)
    	@$(LINKER) $(OBJECTS) $(LFLAGS) -o $@
    	@echo &quot;Linking complete!&quot;
    
    $(OBJECTS): $(OBJDIR)/%.o : $(SRCDIR)/%.c
    	@$(CC) $(CFLAGS) -c $&lt; -o $@
    	@echo &quot;Compiled &quot;$&lt;&quot; successfully!&quot;
     
    .PHONY: clean
    clean:
    	@$(rm) $(OBJECTS)
    	@echo &quot;Cleanup complete!&quot;
    
    .PHONY: remove
    remove: clean
    	@$(rm) $(BINDIR)/$(TARGET)
    	@echo &quot;Executable removed!&quot;


How can I create a Makefile for C projects with SRC, OBJ, and BIN subdirectories?

How can I list the current value of all variables (also called macros) in a Makefile when running make?

E.g. if this is in the Makefile:

    CUR-DIR := $(shell /bin/pwd)
    LOG-DIR := $(CUR-DIR)/make-logs

Then I would like it to tell me:

    CUR-DIR = /home/johv/src/test
    LOG-DIR = /home/johv/src/test/make-logs


gnu make: list the values of all variables (or &quot;macros&quot;) in a particular run

I have a makefile, which includes several other makefiles, which in turn all add to a variable like this:

    VAR := Something SomethingElse
    VAR += SomeOtherThing
    
    (...)

Now I wish to remove `SomethingElse` from the `VAR` variable. What do I put in place of `(...)` to do this?

I am using GNU Make, and a GNU Make specific solution will be fine.

Remove item from a Makefile variable?

What does the following do in a Makefile?

    rule: $(deps)
        @:

I can&#39;t seem to find this in the make manual.

What does @: (at symbol colon) mean in a Makefile?

Usually kernel source are stored in `/usr/src/linux-2.6.x/`.
To avoid to recompile the entire kernel if I modify a module&#39;s source, how can I recompile just that module?

How to recompile just a single kernel module?

I need to get the nth dependency file from a rule, something similar to $n in bash. I need this because I&#39;d like to feed in individual dependency files as options to the build program.

Here&#39;s an example:

    dep.o: dep.src config1.cfg config2.cfg
        parse -cfg1 $2 -cfg2 $3 -o $@ $&lt;

Is it possible?

How to get the second dependency file using Automatic Variables in a Makefile?

`data.table` objects now have a := operator.  What makes this operator different from all other assignment operators?  Also, what are its uses, how much faster is it, and when should it be avoided?

When should I use the := operator in data.table?

What is the difference between `=` and `:=` in Scala?

I have googled extensively for &quot;scala colon-equals&quot;, but was unable to find anything definitive.

What is the difference between = and := in Scala?

What is the best way to assign to multiple columns using `data.table`? For example:

    f &lt;- function(x) {c(&quot;hi&quot;, &quot;hello&quot;)}
    x &lt;- data.table(id = 1:10)

I would like to do something like this (of course this syntax is incorrect):
  
    x[ , (col1, col2) := f(), by = &quot;id&quot;]

And to extend that, I may have many columns with names stored in a variable (say `col_names`) and I would like to do:

    x[ , col_names := another_f(), by = &quot;id&quot;, with = FALSE]

What is the correct way to do something like this?  

Assign multiple columns using := in data.table, by group

What&#39;s happening here? 

    package main
    
    import &quot;fmt&quot;
    
    func main() {
    	
    	myArray  :=[...]int{12,14,26}  ;     
    	fmt.Println(myArray)
    	
    	myArray  :=[...]int{11,12,14} //error pointing on this line 
    	
    	fmt.Println(myArray) ;
    
    }

It throws an error that says 

    no new variables on left side of :=

What I was doing was re-assigning values to an already declared variable.


no new variables on left side of :=

What does the `:=` operand mean, more specifically for Python?

Can someone explain how to read this snippet of code?

    node := root, cost = 0
    frontier := priority queue containing node only
    explored := empty set



Content Type	Original Author	Original Content on Stackoverflow
Question	Aaron Yodaiken	View Question on Stackoverflow
Solution 1 - Makefile	sverre	View Answer on Stackoverflow

:= vs = in make macros

Makefile Problem Overview

Makefile Solutions

Solution 1 - Makefile

MySQL match() against() - order by relevance and column?

Empty/delete a set in Redis?

Attributions