8 Functions for Transforming Text

2 Functions for String Substitution and Analysis

Here are some functions that operate on strings:

$(subst from,to,text)

Performs a textual replacement on the text text: each occurrence of from is replaced by to. The result is substituted for the function call. For example,

$(subst ee,EE,feet on the street)
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produces the value fEEt on the strEEt.

$(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. If replacement also contains a %, the % is replaced by the text that matched the % in pattern. Words that do not match the pattern are kept without change in the output. Only the first % in the pattern and replacement is treated this way; any subsequent % is unchanged.

% characters in patsubst function invocations can be quoted with preceding backslashes \. Backslashes that would otherwise quote % characters can be quoted with more backslashes. Backslashes that quote % characters or other backslashes are removed from the pattern before it is compared file names or has a stem substituted into it. Backslashes that are not in danger of quoting % characters go unmolested. For example, the pattern the\%weird\\%pattern\\ has the%weird\ preceding the operative % character, and pattern\\ following it. The final two backslashes are left alone because they cannot affect any % character.

Whitespace between words is folded into single space characters; leading and trailing whitespace is discarded.

For example,

$(patsubst %.c,%.o,x.c.c bar.c)
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produces the value x.c.o bar.o.

Substitution references (see Substitution References) are a simpler way to get the effect of the patsubst function:

$(var:pattern=replacement)
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is equivalent to

$(patsubst pattern,replacement,$(var))
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The second shorthand simplifies one of the most common uses of patsubst: replacing the suffix at the end of file names.

$(var:suffix=replacement)
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is equivalent to

$(patsubst %suffix,%replacement,$(var))
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For example, you might have a list of object files:

objects = foo.o bar.o baz.o
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To get the list of corresponding source files, you could simply write:

$(objects:.o=.c)
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instead of using the general form:

$(patsubst %.o,%.c,$(objects))
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