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Diffstat (limited to '')
-rw-r--r-- | _posts/2020-05-20-makefile-escaping.md | 28 |
1 files changed, 14 insertions, 14 deletions
diff --git a/_posts/2020-05-20-makefile-escaping.md b/_posts/2020-05-20-makefile-escaping.md index 02c6442..f8db9a0 100644 --- a/_posts/2020-05-20-makefile-escaping.md +++ b/_posts/2020-05-20-makefile-escaping.md @@ -42,19 +42,22 @@ Visit [this page] for an all-in-one Makefile template. * Put the prologue above at the top of your Makefile. * Quote command arguments in Makefiles using single quotes `'`. -* Don't use `'` and `$` in stuff like file paths/environment variable values, -and you're pretty much good to go. * Define a helper function: escape = $(subst ','\'',$(1)) - It protects against quite characters in command arguments. - You can then replace things like `'$(dangerous_variable)'` or `'$(shell -your-command arg1 arg2)'` with `'$(call escape,$(dangerous_variable))'` and -`'$(call escape,$(shell your-command arg1 arg2))'`. + Instead of: + + test: + echo '$(var)' + + do + + test: + echo '$(call escape,$(var))' + * If you use environment variables in your Makefile (or you override variables -on the command line), add the following lengthy snippet to prevent the values -from being expanded: +on the command line), add the following lengthy snippet: define noexpand ifeq ($$(origin $(1)),environment) @@ -272,10 +275,9 @@ These parameters are often defined in a Makefile like this: param_name ?= Default value ``` -They should be quoted when passed to external commands, of course. -To prevent mismatched quotes, the `escape` function might seem useful, but in -case of environment variables, a complication arises when they contain dollar -signs `$`. +They should be `escape`d and quoted when passed to external commands, of +course. +However, things get complicated when they contain dollar signs `$`. `make` variables may contain references to other variables, and they're expanded recursively either when defined (for `:=` assignments) or when used (in all other cases, including `?=`). @@ -413,10 +415,8 @@ endif endef test_var ?= This is safe. -test_var2 ?= This is safe - 2. $(eval $(call noexpand,test_var)) -$(eval $(call noexpand,test_var2)) ``` I couldn't find a case where the combination of `escape` and `noexpand` |