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来自「<B>Digital的Unix操作系统VAX 4.2源码</B>」· 代码 · 共 100 行

CHANGES as of July 12:

1. \ddd allowed in regular expressions.

2. exit <expression> causes the expression to
to be the status return upon completion.

3. a new builtin called "getline" causes the next
input line to be read immediately.  Fields, NR, etc.,
are all set, but you are left at exactly the same place
in the awk program.  Getline returns 0 for end of file;
1 for a normal record.


CHANGES SINCE MEMO:
Update to TM of Sept 1, 1978:

1. A new form of for loop
	for (i in array)
		statement
is now available. It provides a way to walk
along the members of an array, most usefully
for associative arrays with non-numeric subscripts.
Elements are accessed in an unpredictable order,
so don't count on anything.
Futhermore, havoc ensues if elements are created
during this operation, or if the index variable
is fiddled.

2. index(s1, s2) returns the position in s1
where s2 first occurs, or 0 if it doesn't.

3. Multi-line records are now supported more
conveniently. If the record separator is null
	RS = ""
then a blank line terminates a record, and newline
is a default field separator, along with
blank and tab.

4. The syntax of split has been changed.
	n = split(str, arrayname, sep)
splits the string str into the array using
the separator sep (a single character).
If no sep field is given, FS is used instead.
The elements are array[1] ... array[n]; n
is the function value.

5. some minor bugs have been fixed.

IMPLEMENTATION NOTES:

Things to watch out for when trying to make awk:

1. The yacc -d business creates a new file y.tab.h
with the yacc #defines in it. this is compared to
awk.h on each successive compile, and major recompilation
is done only if the files differ. (This permits editing
the grammar file without causing everything in sight
to be recompiled, so long as the definitions don't
change.)

2. The program proc.c is compiled into proc, which
is used to create proctab.c. proctab.c is the
table of function pointers used by run to actually
execute things. Don't try to load proc.c with the
other .c files; it also contains a "main()".

3. Awk uses structure assignment. Be sure your
version of the C compiler has it.

4. The loader flag -lm is used to fetch the standard
math library on the Research system. It is more likely
that you will want to use -lS on yours.
run.c also includes "math.h", which contains sensible
definitions for log(), sqrt(), etc. If you don't have this
include file, comment the line out, and all will be well
anyway.

5. The basic sequence of events (in case make doesn't
seem to do the job) is
	yacc -d awk.g.y
	cc -O -c y.tab.c
	mv y.tab.o awk.g.o
	lex awk.lx.l
	cc -O -c lex.yy.c
	mv lex.yy.o awk.lx.o
	cc -O -c b.c
	cc -O -c main.c
	e - <tokenscript
	cc -O -c token.c
	cc -O -c tran.c
	cc -O -c lib.c
	cc -O -c run.c
	cc -O -c parse.c
	cc -O -c proc.c
	cc -o proc proc.c token.o
	proc >proctab.c
	cc -O -c proctab.c
	cc -i -O awk.g.o awk.lx.o b.o main.o token.o tran.o lib.o run.o parse.o proctab.o -lm