1# This allows us to work with the newline character:
  2define newline
  3
  4
  5endef
  6newline := $(newline)
  7
  8# nl-escape
  9#
 10# Usage: escape = $(call nl-escape[,escape])
 11#
 12# This is used as the common way to specify
 13# what should replace a newline when escaping
 14# newlines; the default is a bizarre string.
 15#
 16nl-escape = $(if $(1),$(1),m822df3020w6a44id34bt574ctac44eb9f4n)
 17
 18# escape-nl
 19#
 20# Usage: escaped-text = $(call escape-nl,text[,escape])
 21#
 22# GNU make's $(shell ...) function converts to a
 23# single space each newline character in the output
 24# produced during the expansion; this may not be
 25# desirable.
 26#
 27# The only solution is to change each newline into
 28# something that won't be converted, so that the
 29# information can be recovered later with
 30# $(call unescape-nl...)
 31#
 32escape-nl = $(subst $(newline),$(call nl-escape,$(2)),$(1))
 33
 34# unescape-nl
 35#
 36# Usage: text = $(call unescape-nl,escaped-text[,escape])
 37#
 38# See escape-nl.
 39#
 40unescape-nl = $(subst $(call nl-escape,$(2)),$(newline),$(1))
 41
 42# shell-escape-nl
 43#
 44# Usage: $(shell some-command | $(call shell-escape-nl[,escape]))
 45#
 46# Use this to escape newlines from within a shell call;
 47# the default escape is a bizarre string.
 48#
 49# NOTE: The escape is used directly as a string constant
 50#       in an `awk' program that is delimited by shell
 51#       single-quotes, so be wary of the characters
 52#       that are chosen.
 53#
 54define shell-escape-nl
 55awk 'NR==1 {t=$$0} NR>1 {t=t "$(nl-escape)" $$0} END {printf t}'
 56endef
 57
 58# shell-unescape-nl
 59#
 60# Usage: $(shell some-command | $(call shell-unescape-nl[,escape]))
 61#
 62# Use this to unescape newlines from within a shell call;
 63# the default escape is a bizarre string.
 64#
 65# NOTE: The escape is used directly as an extended regular
 66#       expression constant in an `awk' program that is
 67#       delimited by shell single-quotes, so be wary
 68#       of the characters that are chosen.
 69#
 70# (The bash shell has a bug where `{gsub(...),...}' is
 71#  misinterpreted as a brace expansion; this can be
 72#  overcome by putting a space between `{' and `gsub').
 73#
 74define shell-unescape-nl
 75awk 'NR==1 {t=$$0} NR>1 {t=t "\n" $$0} END { gsub(/$(nl-escape)/,"\n",t); printf t }'
 76endef
 77
 78# escape-for-shell-sq
 79#
 80# Usage: embeddable-text = $(call escape-for-shell-sq,text)
 81#
 82# This function produces text that is suitable for
 83# embedding in a shell string that is delimited by
 84# single-quotes.
 85#
 86escape-for-shell-sq =  $(subst ','\'',$(1))
 87
 88# shell-sq
 89#
 90# Usage: single-quoted-and-escaped-text = $(call shell-sq,text)
 91#
 92shell-sq = '$(escape-for-shell-sq)'
 93
 94# shell-wordify
 95#
 96# Usage: wordified-text = $(call shell-wordify,text)
 97#
 98# For instance:
 99#
100#  |define text
101#  |hello
102#  |world
103#  |endef
104#  |
105#  |target:
106#  |	echo $(call shell-wordify,$(text))
107#
108# At least GNU make gets confused by expanding a newline
109# within the context of a command line of a makefile rule
110# (this is in constrast to a `$(shell ...)' function call,
111# which can handle it just fine).
112#
113# This function avoids the problem by producing a string
114# that works as a shell word, regardless of whether or
115# not it contains a newline.
116#
117# If the text to be wordified contains a newline, then
118# an intrictate shell command substitution is constructed
119# to render the text as a single line; when the shell
120# processes the resulting escaped text, it transforms
121# it into the original unescaped text.
122#
123# If the text does not contain a newline, then this function
124# produces the same results as the `$(shell-sq)' function.
125#
126shell-wordify = $(if $(findstring $(newline),$(1)),$(_sw-esc-nl),$(shell-sq))
127define _sw-esc-nl
128"$$(echo $(call escape-nl,$(shell-sq),$(2)) | $(call shell-unescape-nl,$(2)))"
129endef
130
131# is-absolute
132#
133# Usage: bool-value = $(call is-absolute,path)
134#
135is-absolute = $(shell echo $(shell-sq) | grep -q ^/ && echo y)
136
137# lookup
138#
139# Usage: absolute-executable-path-or-empty = $(call lookup,path)
140#
141# (It's necessary to use `sh -c' because GNU make messes up by
142#  trying too hard and getting things wrong).
143#
144lookup = $(call unescape-nl,$(shell sh -c $(_l-sh)))
145_l-sh = $(call shell-sq,command -v $(shell-sq) | $(call shell-escape-nl,))
146
147# is-executable
148#
149# Usage: bool-value = $(call is-executable,path)
150#
151# (It's necessary to use `sh -c' because GNU make messes up by
152#  trying too hard and getting things wrong).
153#
154is-executable = $(call _is-executable-helper,$(shell-sq))
155_is-executable-helper = $(shell sh -c $(_is-executable-sh))
156_is-executable-sh = $(call shell-sq,test -f $(1) -a -x $(1) && echo y)
157
158# get-executable
159#
160# Usage: absolute-executable-path-or-empty = $(call get-executable,path)
161#
162# The goal is to get an absolute path for an executable;
163# the `command -v' is defined by POSIX, but it's not
164# necessarily very portable, so it's only used if
165# relative path resolution is requested, as determined
166# by the presence of a leading `/'.
167#
168get-executable = $(if $(1),$(if $(is-absolute),$(_ge-abspath),$(lookup)))
169_ge-abspath = $(if $(is-executable),$(1))
170
171# get-supplied-or-default-executable
172#
173# Usage: absolute-executable-path-or-empty = $(call get-executable-or-default,variable,default)
174#
175define get-executable-or-default
176$(if $($(1)),$(call _ge_attempt,$($(1)),$(1)),$(call _ge_attempt,$(2)))
177endef
178_ge_attempt = $(if $(get-executable),$(get-executable),$(call _gea_err,$(2)))
179_gea_err  = $(if $(1),$(error Please set '$(1)' appropriately))