Function "patsubst" in Makefile

Question

From the docs:

$(patsubst PATTERN,REPLACEMENT,TEXT)

Finds whitespace-separated words in TEXT that match PATTERN and replaces them with REPLACEMENT. Here PATTERN may contain a % which acts as a wildcard, matching any number of any characters within a word.
...
Whitespace between words is folded into single space characters; leading and trailing whitespace is discarded.

Now, given a makefile, is:

# The pattern for patsubst, does NOT contain '%' foo := $(patsubst  x,y,x    x    x) # The pattern for patsubst, does contain '%' bar := $(patsubst x%,y,x    x    x)   # The variable 'foo', is a result from a patsubst-pattern, that did NOT contain a '%' # The variable 'bar', is a result from a patsubst-pattern, that did contain a '%' all ::     @echo 'foo is: "$(foo)"'     @echo 'bar is: "$(bar)"' 

Executing, we get:

foo is: "y    y    y" bar is: "y y y" 

So, it is obvious, that Make, may or may not "fold" all whitespace into one and single whitespace.

Or, did I do something wrong.

Answer 1

In fact all is explained in the doc:

Finds whitespace-separated words in TEXT ...

means that one or more spaces have to separate the words.

... that match PATTERN ...

means that it select only words that match a pattern (which can include some spaces).

... and replaces them with REPLACEMENT.

means that the selected patterns will be replace by a replacement.

---

A picture is worth a thousand words.

For PATTERN = X:

           +----  SEPARATORS  ----+            |                      |    +-------+-------+     +--------+------+    |               |     |               |  X  space space space  X  space space space  x |                     |                     | +---------------------+---------------------+                       |                    PATTERNS 

For PATTERN = X%:

                 +----  SEPARATORS  ---+                  |                     |                +-+-+                 +-+-+                |   |                 |   |  X  space space space  X  space space space  x |            |        |            |        | +------+-----+        +------+-----+        |        |                     |              |        +---  PATTERNS  ------+--------------+ 

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Interesting thing:

When you use the % character in your pattern, you can re-use it in the replacement, like this:

$(patsubst x%,y%,xa xb xc) # Will be "ya yb yc" 

But when you have space character in the % variable, make will strip them in the replacement.

$(patsubst x%,y%,xa   xb   xc) # Will also be "ya yb yc" 

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EDIT: After reading the source code, the interesting things are:

• function.c +146: The function patsubst_expand_pat
• misc.c +337: The function find_next_token
• misc.c +325: The function next_token

So here is the behavior:

1. If no % in the pattern, this is a simple substitution (which keep the spaces).
2. Else it split the text by words and get rid of all spaces (using the isblank function).
3. Finally, it does the replacement