var-op-shell.mk revision 1.5
1 1.5 rillig # $NetBSD: var-op-shell.mk,v 1.5 2022/01/09 18:22:31 rillig Exp $ 2 1.1 rillig # 3 1.2 rillig # Tests for the != variable assignment operator, which runs its right-hand 4 1.2 rillig # side through the shell. 5 1.1 rillig 6 1.3 rillig # The variable OUTPUT gets the output from running the shell command. 7 1.3 rillig OUTPUT!= echo "success"'ful' 8 1.3 rillig .if ${OUTPUT} != "successful" 9 1.3 rillig . error 10 1.3 rillig .endif 11 1.3 rillig 12 1.3 rillig # Since 2014-08-20, the output of the shell command may be empty. 13 1.3 rillig # 14 1.3 rillig # On 1996-05-29, when the '!=' assignment operator and Cmd_Exec were added, 15 1.3 rillig # an empty output produced the error message "Couldn't read shell's output 16 1.3 rillig # for \"%s\"". 17 1.3 rillig # 18 1.5 rillig # The error message is still in Cmd_Exec but reserved for technical errors. 19 1.3 rillig # It may be possible to trigger the error message by killing the shell after 20 1.3 rillig # reading part of its output. 21 1.3 rillig OUTPUT!= true 22 1.3 rillig .if ${OUTPUT} != "" 23 1.3 rillig . error 24 1.3 rillig .endif 25 1.3 rillig 26 1.3 rillig # The output of a shell command that failed is processed nevertheless. 27 1.5 rillig # Unlike the other places that run external commands (expression modifier 28 1.5 rillig # '::!=', expression modifier ':!...!'), a failed command generates only a 29 1.5 rillig # warning, not an "error". These "errors" are ignored in default mode, for 30 1.5 rillig # compatibility, but not in lint mode (-dL). 31 1.3 rillig OUTPUT!= echo "failed"; false 32 1.3 rillig .if ${OUTPUT} != "failed" 33 1.3 rillig . error 34 1.3 rillig .endif 35 1.3 rillig 36 1.3 rillig # A command with empty output may fail as well. 37 1.3 rillig OUTPUT!= false 38 1.3 rillig .if ${OUTPUT} != "" 39 1.3 rillig . error 40 1.3 rillig .endif 41 1.3 rillig 42 1.3 rillig # In the output of the command, each newline is replaced with a space. 43 1.3 rillig # Except for the very last one, which is discarded. 44 1.3 rillig OUTPUT!= echo "line 1"; echo "line 2" 45 1.3 rillig .if ${OUTPUT} != "line 1 line 2" 46 1.3 rillig . error 47 1.3 rillig .endif 48 1.3 rillig 49 1.3 rillig # A failing command in the middle results in the exit status 0, which in the 50 1.3 rillig # end means that the whole sequence of commands succeeded. 51 1.3 rillig OUTPUT!= echo "before"; false; echo "after" 52 1.3 rillig .if ${OUTPUT} != "before after" 53 1.3 rillig . error 54 1.3 rillig .endif 55 1.3 rillig 56 1.4 sjg # This should result in a warning about "exited on a signal". 57 1.4 sjg # This used to be kill -14 (SIGALRM), but that stopped working on 58 1.4 sjg # Darwin18 after recent update. 59 1.4 sjg OUTPUT!= kill $$$$ 60 1.3 rillig .if ${OUTPUT} != "" 61 1.3 rillig . error 62 1.3 rillig .endif 63 1.3 rillig 64 1.3 rillig # A nonexistent command produces a non-zero exit status. 65 1.3 rillig OUTPUT!= /bin/no/such/command 66 1.3 rillig .if ${OUTPUT} != "" 67 1.3 rillig . error 68 1.3 rillig .endif 69 1.3 rillig 70 1.3 rillig # The output from the shell's stderr is not captured, it just passes through. 71 1.3 rillig OUTPUT!= echo "stdout"; echo "stderr" 1>&2 72 1.3 rillig .if ${OUTPUT} != "stdout" 73 1.3 rillig . error 74 1.3 rillig .endif 75 1.3 rillig 76 1.3 rillig # The 8 dollar signs end up as 4 dollar signs when expanded. The shell sees 77 1.3 rillig # the command "echo '$$$$'". The 4 dollar signs are stored in OUTPUT, and 78 1.3 rillig # when that variable is expanded, they expand to 2 dollar signs. 79 1.3 rillig OUTPUT!= echo '$$$$$$$$' 80 1.3 rillig .if ${OUTPUT} != "\$\$" 81 1.3 rillig . error 82 1.3 rillig .endif 83 1.1 rillig 84 1.1 rillig all: 85
Indexes created Mon Sep 29 18:09:42 GMT 2025