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var-op-shell.mk revision 1.4 
      1 # $NetBSD: var-op-shell.mk,v 1.4 2021/02/06 04:55:08 sjg Exp $
      2 #
      3 # Tests for the != variable assignment operator, which runs its right-hand
      4 # side through the shell.
      5 
      6 # The variable OUTPUT gets the output from running the shell command.
      7 OUTPUT!=	echo "success"'ful'
      8 .if ${OUTPUT} != "successful"
      9 .  error
     10 .endif
     11 
     12 # Since 2014-08-20, the output of the shell command may be empty.
     13 #
     14 # On 1996-05-29, when the '!=' assignment operator and Cmd_Exec were added,
     15 # an empty output produced the error message "Couldn't read shell's output
     16 # for \"%s\"".
     17 #
     18 # The error message is still there but reserved for technical errors.
     19 # It may be possible to trigger the error message by killing the shell after
     20 # reading part of its output.
     21 OUTPUT!=	true
     22 .if ${OUTPUT} != ""
     23 .  error
     24 .endif
     25 
     26 # The output of a shell command that failed is processed nevertheless.
     27 # TODO: Make this an error in lint mode.
     28 OUTPUT!=	echo "failed"; false
     29 .if ${OUTPUT} != "failed"
     30 .  error
     31 .endif
     32 
     33 # A command with empty output may fail as well.
     34 OUTPUT!=	false
     35 .if ${OUTPUT} != ""
     36 .  error
     37 .endif
     38 
     39 # In the output of the command, each newline is replaced with a space.
     40 # Except for the very last one, which is discarded.
     41 OUTPUT!=	echo "line 1"; echo "line 2"
     42 .if ${OUTPUT} != "line 1 line 2"
     43 .  error
     44 .endif
     45 
     46 # A failing command in the middle results in the exit status 0, which in the
     47 # end means that the whole sequence of commands succeeded.
     48 OUTPUT!=	echo "before"; false; echo "after"
     49 .if ${OUTPUT} != "before after"
     50 .  error
     51 .endif
     52 
     53 # This should result in a warning about "exited on a signal".
     54 # This used to be kill -14 (SIGALRM), but that stopped working on
     55 # Darwin18 after recent update.
     56 OUTPUT!=	kill $$$$
     57 .if ${OUTPUT} != ""
     58 .  error
     59 .endif
     60 
     61 # A nonexistent command produces a non-zero exit status.
     62 OUTPUT!=	/bin/no/such/command
     63 .if ${OUTPUT} != ""
     64 .  error
     65 .endif
     66 
     67 # The output from the shell's stderr is not captured, it just passes through.
     68 OUTPUT!=	echo "stdout"; echo "stderr" 1>&2
     69 .if ${OUTPUT} != "stdout"
     70 .  error
     71 .endif
     72 
     73 # The 8 dollar signs end up as 4 dollar signs when expanded.  The shell sees
     74 # the command "echo '$$$$'".  The 4 dollar signs are stored in OUTPUT, and
     75 # when that variable is expanded, they expand to 2 dollar signs.
     76 OUTPUT!=	echo '$$$$$$$$'
     77 .if ${OUTPUT} != "\$\$"
     78 .  error
     79 .endif
     80 
     81 all:
     82