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+# This allows us to work with the newline character:
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+define newline
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+
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+
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+endef
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+newline := $(newline)
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+
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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 = $(or $(1),m822df3020w6a44id34bt574ctac44eb9f4n)
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+
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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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+
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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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+
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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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+
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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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+
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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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+
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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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+
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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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+
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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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+
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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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+
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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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+
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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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+
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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 = $(or $(get-executable),$(_gea_warn),$(call _gea_err,$(2)))
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+_gea_warn = $(warning The path '$(1)' is not executable.)
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+_gea_err = $(if $(1),$(error Please set '$(1)' appropriately))
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Michael Witten