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var-op-shell.mk revision 1.3 
      1 # $NetBSD: var-op-shell.mk,v 1.3 2020/11/09 20:39:46 rillig 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 # NB: The signal number must be numeric since some shells (which ones?) don't
     54 # accept symbolic signal names.  14 is typically SIGALRM.
     55 #
     56 # XXX: The number of the signal is not mentioned in the warning since that
     57 # would have been difficult to implement; currently the errfmt is a format
     58 # string containing a single %s conversion.
     59 OUTPUT!=	kill -14 $$$$
     60 .if ${OUTPUT} != ""
     61 .  error
     62 .endif
     63 
     64 # A nonexistent command produces a non-zero exit status.
     65 OUTPUT!=	/bin/no/such/command
     66 .if ${OUTPUT} != ""
     67 .  error
     68 .endif
     69 
     70 # The output from the shell's stderr is not captured, it just passes through.
     71 OUTPUT!=	echo "stdout"; echo "stderr" 1>&2
     72 .if ${OUTPUT} != "stdout"
     73 .  error
     74 .endif
     75 
     76 # The 8 dollar signs end up as 4 dollar signs when expanded.  The shell sees
     77 # the command "echo '$$$$'".  The 4 dollar signs are stored in OUTPUT, and
     78 # when that variable is expanded, they expand to 2 dollar signs.
     79 OUTPUT!=	echo '$$$$$$$$'
     80 .if ${OUTPUT} != "\$\$"
     81 .  error
     82 .endif
     83 
     84 all:
     85