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      1  1.1  rillig # $NetBSD: cmdline-redirect-stdin.mk,v 1.1 2021/02/01 20:31:41 rillig Exp $
      2  1.1  rillig #
      3  1.1  rillig # Demonstrate that the '!=' assignment operator can read individual lines
      4  1.1  rillig # from make's stdin.
      5  1.1  rillig #
      6  1.1  rillig # This edge case is an implementation detail that has no practical
      7  1.1  rillig # application.
      8  1.1  rillig 
      9  1.1  rillig all: .PHONY
     10  1.1  rillig 	@printf '%s\n' "first line" "second line" \
     11  1.1  rillig 	| ${MAKE} -f ${MAKEFILE} read-lines
     12  1.1  rillig 
     13  1.1  rillig .if make(read-lines)
     14  1.1  rillig line1!=		read line; echo "$$line"
     15  1.1  rillig line2!=		read line; echo "$$line"
     16  1.1  rillig 
     17  1.1  rillig .if ${line1} != "first line"
     18  1.1  rillig .  error line1="${line1}"
     19  1.1  rillig 
     20  1.1  rillig .elif ${line2} == ""
     21  1.1  rillig # If this branch is ever reached, the shell from the assignment to line1
     22  1.1  rillig # probably buffers its input.  Most shells use unbuffered stdin, and this
     23  1.1  rillig # is actually specified by POSIX, which says that "The read utility shall
     24  1.1  rillig # read a single line from standard input".  This is the reason why the shell
     25  1.1  rillig # reads its input byte by byte, which makes it terribly slow for practical
     26  1.1  rillig # applications.
     27  1.1  rillig .  error The shell's read command does not read a single line.
     28  1.1  rillig 
     29  1.1  rillig .elif ${line2} != "second line"
     30  1.1  rillig .  error line2="${line2}"
     31  1.1  rillig .endif
     32  1.1  rillig 
     33  1.1  rillig read-lines: .PHONY
     34  1.1  rillig .endif
     35