180 lines
5.2 KiB
Makefile
180 lines
5.2 KiB
Makefile
# This allows us to work with the newline character:
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define newline
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endef
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newline := $(newline)
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# nl-escape
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#
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# Usage: escape = $(call nl-escape[,escape])
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#
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# This is used as the common way to specify
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# what should replace a newline when escaping
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# newlines; the default is a bizarre string.
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#
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nl-escape = $(if $(1),$(1),m822df3020w6a44id34bt574ctac44eb9f4n)
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# escape-nl
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#
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# Usage: escaped-text = $(call escape-nl,text[,escape])
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#
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# GNU make's $(shell ...) function converts to a
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# single space each newline character in the output
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# produced during the expansion; this may not be
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# desirable.
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#
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# The only solution is to change each newline into
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# something that won't be converted, so that the
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# information can be recovered later with
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# $(call unescape-nl...)
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#
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escape-nl = $(subst $(newline),$(call nl-escape,$(2)),$(1))
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# unescape-nl
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#
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# Usage: text = $(call unescape-nl,escaped-text[,escape])
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#
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# See escape-nl.
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#
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unescape-nl = $(subst $(call nl-escape,$(2)),$(newline),$(1))
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# shell-escape-nl
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#
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# Usage: $(shell some-command | $(call shell-escape-nl[,escape]))
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#
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# Use this to escape newlines from within a shell call;
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# the default escape is a bizarre string.
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#
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# NOTE: The escape is used directly as a string constant
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# in an `awk' program that is delimited by shell
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# single-quotes, so be wary of the characters
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# that are chosen.
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#
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define shell-escape-nl
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awk 'NR==1 {t=$$0} NR>1 {t=t "$(nl-escape)" $$0} END {printf t}'
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endef
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# shell-unescape-nl
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#
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# Usage: $(shell some-command | $(call shell-unescape-nl[,escape]))
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#
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# Use this to unescape newlines from within a shell call;
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# the default escape is a bizarre string.
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#
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# NOTE: The escape is used directly as an extended regular
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# expression constant in an `awk' program that is
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# delimited by shell single-quotes, so be wary
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# of the characters that are chosen.
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#
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# (The bash shell has a bug where `{gsub(...),...}' is
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# misinterpreted as a brace expansion; this can be
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# overcome by putting a space between `{' and `gsub').
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#
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define shell-unescape-nl
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awk 'NR==1 {t=$$0} NR>1 {t=t "\n" $$0} END { gsub(/$(nl-escape)/,"\n",t); printf t }'
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endef
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# escape-for-shell-sq
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#
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# Usage: embeddable-text = $(call escape-for-shell-sq,text)
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#
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# This function produces text that is suitable for
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# embedding in a shell string that is delimited by
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# single-quotes.
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#
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escape-for-shell-sq = $(subst ','\'',$(1))
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# shell-sq
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#
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# Usage: single-quoted-and-escaped-text = $(call shell-sq,text)
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#
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shell-sq = '$(escape-for-shell-sq)'
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# shell-wordify
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#
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# Usage: wordified-text = $(call shell-wordify,text)
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#
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# For instance:
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#
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# |define text
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# |hello
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# |world
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# |endef
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# |
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# |target:
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# | echo $(call shell-wordify,$(text))
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#
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# At least GNU make gets confused by expanding a newline
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# within the context of a command line of a makefile rule
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# (this is in constrast to a `$(shell ...)' function call,
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# which can handle it just fine).
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#
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# This function avoids the problem by producing a string
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# that works as a shell word, regardless of whether or
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# not it contains a newline.
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#
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# If the text to be wordified contains a newline, then
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# an intrictate shell command substitution is constructed
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# to render the text as a single line; when the shell
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# processes the resulting escaped text, it transforms
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# it into the original unescaped text.
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#
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# If the text does not contain a newline, then this function
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# produces the same results as the `$(shell-sq)' function.
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#
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shell-wordify = $(if $(findstring $(newline),$(1)),$(_sw-esc-nl),$(shell-sq))
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define _sw-esc-nl
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"$$(echo $(call escape-nl,$(shell-sq),$(2)) | $(call shell-unescape-nl,$(2)))"
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endef
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# is-absolute
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#
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# Usage: bool-value = $(call is-absolute,path)
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#
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is-absolute = $(shell echo $(shell-sq) | grep -q ^/ && echo y)
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# lookup
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#
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# Usage: absolute-executable-path-or-empty = $(call lookup,path)
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#
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# (It's necessary to use `sh -c' because GNU make messes up by
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# trying too hard and getting things wrong).
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#
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lookup = $(call unescape-nl,$(shell sh -c $(_l-sh)))
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_l-sh = $(call shell-sq,command -v $(shell-sq) | $(call shell-escape-nl,))
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# is-executable
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#
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# Usage: bool-value = $(call is-executable,path)
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#
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# (It's necessary to use `sh -c' because GNU make messes up by
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# trying too hard and getting things wrong).
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#
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is-executable = $(call _is-executable-helper,$(shell-sq))
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_is-executable-helper = $(shell sh -c $(_is-executable-sh))
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_is-executable-sh = $(call shell-sq,test -f $(1) -a -x $(1) && echo y)
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# get-executable
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#
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# Usage: absolute-executable-path-or-empty = $(call get-executable,path)
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#
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# The goal is to get an absolute path for an executable;
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# the `command -v' is defined by POSIX, but it's not
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# necessarily very portable, so it's only used if
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# relative path resolution is requested, as determined
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# by the presence of a leading `/'.
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#
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get-executable = $(if $(1),$(if $(is-absolute),$(_ge-abspath),$(lookup)))
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_ge-abspath = $(if $(is-executable),$(1))
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# get-supplied-or-default-executable
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#
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# Usage: absolute-executable-path-or-empty = $(call get-executable-or-default,variable,default)
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#
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define get-executable-or-default
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$(if $($(1)),$(call _ge_attempt,$($(1)),$(1)),$(call _ge_attempt,$(2)))
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endef
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_ge_attempt = $(if $(get-executable),$(get-executable),$(call _gea_err,$(2)))
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_gea_err = $(if $(1),$(error Please set '$(1)' appropriately))
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