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<div class="node">
<p>
Node:<a name="Origin%20Function">Origin Function</a>,
Next:<a rel="next" accesskey="n" href="Shell-Function.html#Shell%20Function">Shell Function</a>,
Previous:<a rel="previous" accesskey="p" href="Eval-Function.html#Eval%20Function">Eval Function</a>,
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<h3 class="section">The <code>origin</code> Function</h3>

   <p>The <code>origin</code> function is unlike most other functions in that it does
not operate on the values of variables; it tells you something <em>about</em>
a variable.  Specifically, it tells you where it came from.

   <p>The syntax of the <code>origin</code> function is:

<pre class="example">     $(origin <var>variable</var>)
     </pre>

   <p>Note that <var>variable</var> is the <em>name</em> of a variable to inquire about;
not a <em>reference</em> to that variable.  Therefore you would not normally
use a <code>$</code> or parentheses when writing it.  (You can, however, use a
variable reference in the name if you want the name not to be a constant.)

   <p>The result of this function is a string telling you how the variable
<var>variable</var> was defined:

     <dl>
<dt><code>undefined</code>
     <dd>
if <var>variable</var> was never defined.

     <br><dt><code>default</code>
     <dd>
if <var>variable</var> has a default definition, as is usual with <code>CC</code>
and so on.  See <a href="Implicit-Variables.html#Implicit%20Variables">Variables Used by Implicit Rules</a>.
Note that if you have redefined a default variable, the <code>origin</code>
function will return the origin of the later definition.

     <br><dt><code>environment</code>
     <dd>
if <var>variable</var> was defined as an environment variable and the
<code>-e</code> option is <em>not</em> turned on (see <a href="Options-Summary.html#Options%20Summary">Summary of Options</a>).

     <br><dt><code>environment override</code>
     <dd>
if <var>variable</var> was defined as an environment variable and the
<code>-e</code> option <em>is</em> turned on (see <a href="Options-Summary.html#Options%20Summary">Summary of Options</a>).

     <br><dt><code>file</code>
     <dd>
if <var>variable</var> was defined in a makefile.

     <br><dt><code>command line</code>
     <dd>
if <var>variable</var> was defined on the command line.

     <br><dt><code>override</code>
     <dd>
if <var>variable</var> was defined with an <code>override</code> directive in a
makefile (see <a href="Override-Directive.html#Override%20Directive">The <code>override</code> Directive</a>).

     <br><dt><code>automatic</code>
     <dd>
if <var>variable</var> is an automatic variable defined for the
execution of the commands for each rule
(see <a href="Automatic.html#Automatic">Automatic Variables</a>).
</dl>

   <p>This information is primarily useful (other than for your curiosity) to
determine if you want to believe the value of a variable.  For example,
suppose you have a makefile <code>foo</code> that includes another makefile
<code>bar</code>.  You want a variable <code>bletch</code> to be defined in <code>bar</code>
if you run the command <code>make&nbsp;-f&nbsp;bar</code>, even if the environment contains
a definition of <code>bletch</code>.  However, if <code>foo</code> defined
<code>bletch</code> before including <code>bar</code>, you do not want to override that
definition.  This could be done by using an <code>override</code> directive in
<code>foo</code>, giving that definition precedence over the later definition in
<code>bar</code>; unfortunately, the <code>override</code> directive would also
override any command line definitions.  So, <code>bar</code> could
include:

<pre class="example">     ifdef bletch
     ifeq "$(origin bletch)" "environment"
     bletch = barf, gag, etc.
     endif
     endif
     </pre>

<p>If <code>bletch</code> has been defined from the environment, this will redefine
it.

   <p>If you want to override a previous definition of <code>bletch</code> if it came
from the environment, even under <code>-e</code>, you could instead write:

<pre class="example">     ifneq "$(findstring environment,$(origin bletch))" ""
     bletch = barf, gag, etc.
     endif
     </pre>

   <p>Here the redefinition takes place if <code>$(origin bletch)</code> returns either
<code>environment</code> or <code>environment override</code>.
See <a href="Text-Functions.html#Text%20Functions">Functions for String Substitution and Analysis</a>.

   </body></html>