Variable Edit Operators

Feature Description

Variable edit operators allow variable values to be tested and modified during expansion. There are approximately 60 different edit operators which can perform many useful tasks, such as pattern matching, path manipulation, changing strings of characters, etc. Edit operators are often used to manipulate a list stored in a variable, such as a list of file names. Each string, separated by white space, contained in a variable is called a token and edit operations can apply to each token or to the variable as a whole. They can also be pipelined to form arbitrarily complex editing operations.

Impact

Productivity

• Simplifies makefiles by providing a simple and flexible means of modifying variable values.
• Using edit operators is less error prone than programming manual modifications.

Consequence of Not Having the Feature

• Performing operations on variable values would require more development effort since they would need to be manually programmed.
• Larger, more complicated makefiles.

Examples

Here are some of commonly used edit operators.

$ cat Makefile 
FILES = src1/a.c src1/b.c src1/c.c src2/d.c src2/e.c
DIRS  = src1 src2 hdr obj

example : .MAKE
        print 1 - $(FILES:C/1/3/g)
        print 2 - $(FILES:D)
        print 3 - $(FILES:D:O=1)
        print 4 - $(FILES:D=src:B:S)
        print 5 - $(FILES:B:S=.o)
        print 6 - $(DIRS:L)
        print 7 - $(DIRS:N=src*)
        print 8 - $(DIRS:N=src*:L=*.c)
        print 9 - $(".":L:N=obj:Y??mkdir obj?)

$ ls src1
a.c  a.h  b.c  b.h  c.c

$ ls src2
d.c  d.h  e.c

$ ls obj
ls: obj: No such file or directory

$ nmake
1 - src3/a.c src3/b.c src3/c.c src2/d.c src2/e.c
2 - src1 src1 src1 src2 src2
3 - src1
4 - src/a.c src/b.c src/c.c src/d.c src/e.c
5 - a.o b.o c.o d.o e.o
6 - a.c b.c c.c d.c e.c a.h b.h d.h
7 - src1 src2
8 - a.c b.c c.c d.c e.c
9 - mkdir obj