1 files changed, 103 insertions, 0 deletions
diff --git a/src/substvars.sh b/src/substvars.sh
new file mode 100644
index 0000000..c2bc3f8
--- /dev/null
+++ b/src/substvars.sh
@@ -0,0 +1,103 @@
+# Functions for setting and substituting variables
+#
+# Copyright (C) 2012, 2014  Patrick "P. J." McDermott
+#
+# This file is part of the ProteanOS Development Kit.
+#
+# The ProteanOS Development Kit is free software: you can redistribute
+# it and/or modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation, either version 3 of the
+# License, or (at your option) any later version.
+#
+# The ProteanOS Development Kit is distributed in the hope that it
+# will be useful, but WITHOUT ANY WARRANTY; without even the implied
+# warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+# See the GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with the ProteanOS Development Kit.  If not, see
+# <http://www.gnu.org/licenses/>.
+
+substvars_max_depth=50
+
+set_substvar()
+{
+	local name="${1}"
+	local value="${2}"
+
+	# Convert variable name to lower case and validate.
+	name="$(printf '%s\n' "${name}" | tr 'A-Z-' 'a-z_')"
+	case "${name:- }" in
+		*[!a-z0-9_]*)
+			warn "$(get_msg 'substvar_invalid')" "${name}"
+			return 1
+			;;
+	esac
+
+	# Trim leading and trailing newline characters from value.
+	value="$(printf '%s\n' "${value}" | sed -n '
+		H;            # Store each input line in the hold space.
+		${            # At the last line of input:
+		  g;          # Restore the hold space into the pattern space.
+		  s/^[\n]*//; # Remove leading newline characters.
+		  s/[\n]*$//; # Remove trailing newline characters.
+		  p;          # Print the results.
+		};
+		')"
+
+	# Escape single quotes in value.
+	value="$(printf '%s\n' "${value}" | sed "s/'/'\\\\''/g")"
+
+	eval "substvar_${name}='${value}'"
+
+	return 0
+}
+
+substvars()
+{
+	local string="${1}"
+	local depth=
+	local lhs=
+	local name=
+	local rhs=
+	local old_rhs=
+	local value=
+
+	# Logic inspired by that of dpkg's Dpkg::Substvars::substvars()
+	# subroutine.
+
+	depth=0
+
+	while :; do
+		lhs="${string%%\$\{*}"
+		if [ ${#lhs} -eq ${#string} ]; then
+			# No "${" was found.
+			break
+		fi
+		string="${string#*\$\{}"
+		name="${string%%\}*}"
+		rhs="${string#*\}}"
+
+		if [ ${#rhs} -lt ${#old_rhs} ]; then
+			# Reset the nesting counter if we've advanced the right
+			# side of the matched space.
+			depth=0
+		fi
+		if [ ${depth} -ge ${substvars_max_depth} ]; then
+			# Warn of possible recursion.
+			warn "$(get_msg 'substvar_deep_nesting')"
+			return 1
+		fi
+		old_rhs="${rhs}"
+
+		# Perform the substitution.
+		name="$(printf '%s\n' "${name}" | tr 'A-Z-' 'a-z_')"
+		value="$(eval "printf '%s\n' \"\${substvar_${name}}\"")"
+		string="${lhs}${value}${rhs}"
+		depth=$(($depth + 1))
+	done
+
+	printf '%s\n' "${string}"
+
+	return 0
+}