Variables need not always be expanded verbatim. PMake defines several modifiers that may be applied to a variable's value before it is expanded. You apply a modifier by placing it after the variable name with a colon between the two, like so:
${VARIABLE:modifier}
Each modifier is a single character followed by something specific to the modifier itself. You may apply as many modifiers as you want – each one is applied to the result of the previous and is separated from the previous by another colon.
There are seven ways to modify a variable's expansion, most of which come from the C shell variable modification characters:
This is used to select only those words (a word is a series of characters that
are neither spaces nor tabs) that match the given pattern. The pattern is a
wildcard pattern like that used by the shell, where *
means 0 or more characters of any sort; ? is any single character; [abcd]
matches any single character that is either a, b, c or d
(there may be any number of characters between the brackets); [0-9] matches any single character that is between 0 and 9 (i.e. any digit. This form
may be freely mixed with the other bracket form), and \ is used to escape any of the characters *, ?, [ or
:, leaving them as regular characters to match themselves
in a word. For example, the system makefile <makedepend.mk> uses $(CFLAGS:M-[ID]*) to extract all the -I and -D flags that would be
passed to the C compiler. This allows it to properly locate include files and
generate the correct dependencies.
This is identical to :M except it substitutes all words that do not match the given pattern.
Causes the first occurrence of search-string in the variable to be replaced by
replacement-string, unless the g flag is given at the
end, in which case all occurrences of the string are replaced. The
substitution is performed on each word in the variable in turn. If search-string
begins with a ^, the string must match starting at
the beginning of the word. If search-string ends with a $,
the string must match to the end of the word (these two may be combined to force an
exact match). If a backslash precedes these two characters, however, they
lose their special meaning. Variable expansion also occurs in the normal fashion
inside both the search-string and the replacement-string, except that a
backslash is used to prevent the expansion of a $, not
another dollar sign, as is usual. Note that search-string is just a string, not a
pattern, so none of the usual regularexpression/wildcard characters have any
special meaning save ^ and $. In
the replacement string, the & character is
replaced by the search-string unless it is preceded by a backslash. You are allowed
to use any character except colon or exclamation point to separate the two
strings. This so-called delimiter character may be placed in either string by
preceding it with a backslash.
Replaces each word in the variable expansion by its last component (its “tail”). For example, given:
OBJS = ../lib/a.o b /usr/lib/libm.a TAILS = $(OBJS:T)
the variable TAILS would expand to a.o b libm.a.
This is similar to :T, except that every word is replaced by everything but the tail (the “head”). Using the same definition of OBJS, the string $(OBJS:H) would expand to ../lib /usr/lib. Note that the final slash on the heads is removed and anything without a head is replaced by the empty string.
:E replaces each word by its suffix (“extension”). So $(OBJS:E) would give you .o .a.
This replaces each word by everything but the suffix (the “root” of the word). $(OBJS:R) expands to ../lib/a b /usr/lib/libm.
In addition, the System V style of substitution is also supported. This looks like:
$(VARIABLE:search-string=replacement)
It must be the last modifier in the chain. The search is anchored at the end of each word, so only suffixes or whole words may be replaced.