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Diffstat (limited to '_posts/2020-05-20-makefile-escaping.md')
| -rw-r--r-- | _posts/2020-05-20-makefile-escaping.md | 158 |
1 files changed, 112 insertions, 46 deletions
diff --git a/_posts/2020-05-20-makefile-escaping.md b/_posts/2020-05-20-makefile-escaping.md index 90acf85..f3d301e 100644 --- a/_posts/2020-05-20-makefile-escaping.md +++ b/_posts/2020-05-20-makefile-escaping.md @@ -84,8 +84,7 @@ scripts. This is to prevent a single argument from being expanded into multiple arguments by the shell. -``` -$ cat Makefile +{% capture out1 %} # Prologue goes here... test_var := Same line? @@ -96,15 +95,19 @@ test: @printf '%s\n' '$(test_var)' @printf '%s\n' $$test_var @printf '%s\n' "$$test_var" +{% endcapture %} -$ make test +{% capture out2 %} Same line? Same line? Same line? Same line? -``` +{% endcapture %} + +{% include shell.html cmd='cat Makefile' out=out1 %} +{% include shell.html cmd='make test' out=out2 %} This is quite often sufficient to write valid recipes. @@ -119,28 +122,30 @@ What if `test_var` included a single quote `'`? In that case, even the quoted `printf` invocation would break because of the mismatch. -``` -$ cat Makefile +{% capture out1 %} # Prologue goes here... test_var := Includes ' quote test: printf '%s\n' '$(test_var)' +{% endcapture %} -$ make test +{% capture out2 %} printf '%s\n' 'Includes ' quote' bash: -c: line 0: unexpected EOF while looking for matching `'' make: *** [Makefile:11: test] Error 2 -``` +{% endcapture %} + +{% include shell.html cmd='cat Makefile' out=out1 %} +{% include shell.html cmd='make test' out=out2 %} One solution is to take advantage of how `bash` parses command arguments, and replace every quote `'` by `'\''`. This works because `bash` merges a string like `'Includes '\'' quote'` into `Includes ' quote`. -``` -$ cat Makefile +{% capture out1 %} # Prologue goes here... escape = $(subst ','\'',$(1)) @@ -149,11 +154,15 @@ test_var := Includes ' quote test: printf '%s\n' '$(call escape,$(test_var))' +{% endcapture %} -$ make test +{% capture out2 %} printf '%s\n' 'Includes '\'' quote' Includes ' quote -``` +{% endcapture %} + +{% include shell.html cmd='cat Makefile' out=out1 %} +{% include shell.html cmd='make test' out=out2 %} Surprisingly, this works even in much more complicated cases. You can have a recipe that executes a command that takes a whole other command @@ -161,8 +170,7 @@ You can have a recipe that executes a command that takes a whole other command I guess the most common use case is doing something like `ssh 'rm -rf $(junk_dir)'`, but I'll use nested `bash` calls instead for simplicity. -``` -$ cat Makefile +{% capture out1 %} # Prologue goes here... escape = $(subst ','\'',$(1)) @@ -176,15 +184,19 @@ test: printf '%s\n' '$(call escape,$(test_var))' bash -c '$(call escape,$(echo_test_var))' bash -c '$(call escape,$(bash_test_var))' +{% endcapture %} -$ make test +{% capture out2 %} printf '%s\n' 'Includes '\'' quote' Includes ' quote bash -c 'printf '\''%s\n'\'' '\''Includes '\''\'\'''\'' quote'\''' Includes ' quote bash -c 'bash -c '\''printf '\''\'\'''\''%s\n'\''\'\'''\'' '\''\'\'''\''Includes '\''\'\'''\''\'\''\'\'''\'''\''\'\'''\'' quote'\''\'\'''\'''\''' Includes ' quote -``` +{% endcapture %} + +{% include shell.html cmd='cat Makefile' out=out1 %} +{% include shell.html cmd='make test' out=out2 %} That's somewhat insane, but it works. @@ -196,8 +208,7 @@ outside world in a Makefile (the other being environment variables). This little `escape` function we've defined is actually sufficient to deal with the output of the `shell` function safely. -``` -$ cat Makefile +{% capture out1 %} # Prologue goes here... escape = $(subst ','\'',$(1)) @@ -211,19 +222,42 @@ composite_var := Composite value - $(simple_var) - $(cwd) test: @printf '%s\n' '$(call escape,$(cwd))' @printf '%s\n' '$(call escape,$(composite_var))' - -$ ( mkdir -p -- "Includes ' quote" && cd -- "Includes ' quote" && make -f ../Makefile test ; ) +{% endcapture %} + +{% capture cmd2 %} +mkdir "Includes ' quote" && \ + cd "Includes ' quote" && \ + make -f ../Makefile test +{% endcapture %} +{% capture out2 %} Includes ' quote Composite value - Simple value - Includes ' quote - -$ ( mkdir -p -- 'Maybe a comment #' && cd -- 'Maybe a comment #' && make -f ../Makefile test ; ) +{% endcapture %} + +{% capture cmd3 %} +mkdir 'Maybe a comment #' && \ + cd 'Maybe a comment #' && \ + make -f ../Makefile test +{% endcapture %} +{% capture out3 %} Maybe a comment # Composite value - Simple value - Maybe a comment # - -$ ( mkdir -p -- 'Variable ${reference}' && cd -- 'Variable ${reference}' && make -f ../Makefile test ; ) +{% endcapture %} + +{% capture cmd4 %} +mkdir 'Variable ${reference}' && \ + cd 'Variable ${reference}' && \ + make -f ../Makefile test +{% endcapture %} +{% capture out4 %} Variable ${reference} Composite value - Simple value - Variable ${reference} -``` +{% endcapture %} + +{% include shell.html cmd='cat Makefile' out=out1 %} +{% include shell.html cmd=cmd2 out=out2 %} +{% include shell.html cmd=cmd3 out=out3 %} +{% include shell.html cmd=cmd4 out=out4 %} Environment variables --------------------- @@ -246,9 +280,7 @@ signs `$`. expanded recursively either when defined (for `:=` assignments) or when used (in all other cases, including `?=`). - -``` -$ cat Makefile +{% capture out1 %} # Prologue goes here... escape = $(subst ','\'',$(1)) @@ -260,30 +292,40 @@ export test_var test: @printf '%s\n' '$(call escape,$(test_var))' @printf '%s\n' "$$test_var" +{% endcapture %} -$ test_var='Variable ${reference}' make test +{% capture cmd2 %} +test_var='Variable ${reference}' make test +{% endcapture %} +{% capture out2 %} Makefile:15: warning: undefined variable 'reference' Variable Variable ${reference} -``` +{% endcapture %} + +{% include shell.html cmd='cat Makefile' out=out1 %} +{% include shell.html cmd=cmd2 out=out2 %} Here, `$(test_var)` is expanded recursively, substituting an empty string for the `${reference}` part. One attempt to solve this is to escape the dollar sign in the variable value, but that breaks the `"$$test_var"` case: -``` -$ test_var='Variable $${reference}' make test +{% capture cmd1 %} +test_var='Variable $${reference}' make test +{% endcapture %} +{% capture out1 %} Variable ${reference} Variable $${reference} -``` +{% endcapture %} + +{% include shell.html cmd=cmd1 out=out1 %} A working solution would be to use the `escape` function on the unexpanded variable value. Turns out, you can do just that using the `value` function in `make`. -``` -$ cat Makefile +{% capture out1 %} # Prologue goes here... escape = $(subst ','\'',$(1)) @@ -296,24 +338,35 @@ export test_var test: @printf '%s\n' '$(call escape,$(test_var))' @printf '%s\n' "$$test_var" +{% endcapture %} -$ test_var="Quote '"' and variable ${reference}' make test +{% capture cmd2 %} +test_var="Quote '"' and variable ${reference}' make test +{% endcapture %} +{% capture out2 %} Quote ' and variable ${reference} Quote ' and variable ${reference} -``` +{% endcapture %} + +{% include shell.html cmd='cat Makefile' out=out1 %} +{% include shell.html cmd=cmd2 out=out2 %} This doesn't quite work though when [overriding variables] on the command line. For example, this doesn't work: [overriding variables]: https://www.gnu.org/software/make/manual/html_node/Overriding.html#Overriding -``` -$ make test test_var='Variable ${reference}' +{% capture cmd1 %} +make test test_var='Variable ${reference}' +{% endcapture %} +{% capture out1 %} Makefile:16: warning: undefined variable 'reference' make: warning: undefined variable 'reference' Variable Variable -``` +{% endcapture %} + +{% include shell.html cmd=cmd1 out=out1 %} This is because `make` ignores all assignments to `test_var` if it's overridden on the command line (including `test_var := $(value test_var)`). @@ -371,8 +424,7 @@ wouldn't work. You can even safely use other variable as the default value of `test_var`, and it works: -``` -> cat Makefile +{% capture out1 %} # Prologue goes here... escape = $(subst ','\'',$(1)) @@ -401,16 +453,30 @@ composite_var := Composite value - $(simple_var) - $(test_var) test: @printf '%s\n' '$(call escape,$(test_var))' @printf '%s\n' '$(call escape,$(composite_var))' +{% endcapture %} -> make test +{% capture out2 %} New simple value in test_var Composite value - New simple value - New simple value in test_var +{% endcapture %} -> make test test_var='Variable ${reference}' +{% capture cmd3 %} +make test test_var='Variable ${reference}' +{% endcapture %} +{% capture out3 %} Variable ${reference} Composite value - New simple value - Variable ${reference} +{% endcapture %} -> test_var='Variable ${reference}' make test +{% capture cmd4 %} +test_var='Variable ${reference}' make test +{% endcapture %} +{% capture out4 %} Variable ${reference} Composite value - New simple value - Variable ${reference} -``` +{% endcapture %} + +{% include shell.html cmd='cat Makefile' out=out1 %} +{% include shell.html cmd='make test' out=out2 %} +{% include shell.html cmd=cmd3 out=out3 %} +{% include shell.html cmd=cmd4 out=out4 %} |