initial commit.

.gitignore

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+pkg/
+default/

LICENSE

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+The MIT License (MIT)
+
+Copyright 2020 "yafox"
+
+Permission is hereby granted, free of charge, to any person obtaining a copy of
+this software and associated documentation files (the "Software"), to deal in
+the Software without restriction, including without limitation the rights to
+use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
+the Software, and to permit persons to whom the Software is furnished to do so,
+subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
+IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

README

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+# how.sh
+
+takes a package name, a version, and a path.  mounts scripts for patching,
+configuring, building, and installing the given version of the package at the
+given path in read-only mode using either overlayfs or, if no package-specific
+scripts were found, a bind mount.
+
+dependencies: `shsort` and `vercmp`, as well as 'how-defaults' and 'how-pkgs'
+repositories.  (see makefile.)
+
+55 SLOC.
+
+usage: how <package> <version> <path>
+
+## package structure
+
+if a package or version is not recognized, how.sh will bind-mount the `default`
+directory in read-only mode at the requested path.  a package and version is
+recognized based on the presence of a subdirectory in the `pkg` directory
+matching the package name with a subdirectory whose name translates to a version
+equal to or less than version of the package requested, or a subdirectory named
+`default`.  the structure looks something like this:
+
+    pkg/
+    |-- <package>/
+    |   |-- <version>/
+    ...
+
+`version` is matched using `vercmp`.  if `vercmp` has a format that matches the
+package name, then that format is used to compare versions for the package.
+otherwise, the default comparison function is used.
+
+the version directories are sorted using `shsort` and `vercmp` and mounted as an
+overlay filesystem with the lower versions being lower in the overlay and higher
+versions being higher.  `default` package subdirectories are always one layer
+above the `default` directory;  the `default` directory is always lowest.
+
+## patches
+
+multiple patches may be offered in a package.  by convention, patches are kept
+in the `patches` subdirectory of the package root.  the default `patch` command
+looks for a single combined patch, likely constructed by concatenating or
+otherwise combining offered patches, under the filename `patch` in the package
+root.

USAGE

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+usage: $(basename $0) <package> <version> [<path>]
+
+arguments:
+    <package>: name of the package to examine.
+    <version>: version of the package to examine.
+    [<path>]: mount path for 'how' scripts. prints "lowerdir" string if omitted.

how.sh

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+#!/usr/bin/env sh
+set -e
+
+HOWROOT="${HOWROOT:-$(dirname "$(readlink -f "$0")")}"
+
+if [ ! -d "$HOWROOT" ]; then
+    echo "$HOWROOT is not a directory!" >&2
+    exit 1
+fi
+
+{ [ "$1" ] && [ "$2" ]; } \
+|| { eval "echo \"$(cat "$HOWROOT/USAGE")\"" && exit 0; }
+
+. "$HOWROOT/lib/log.sh"
+
+pkg="$1"
+ver="$2"
+tgt="$3"
+
+if [ "$tgt" ] && [ ! -d "$tgt" ]; then
+    echo "$tgt isn't a directory!" >&2
+    exit 1
+fi
+
+{ vercmp formats | grep -q "^$pkg"; } \
+&& fmt="$pkg" \
+|| fmt="default"
+
+[ ! -d "$HOWROOT/pkg/$pkg/default" ] || layers="$HOWROOT/pkg/$pkg/default:"
+
+if [ -d "$HOWROOT/pkg/$pkg" ]; then
+    layers="$(ls -d $HOWROOT/pkg/$pkg/*/ \
+    | rev | cut -d/ -f2 | rev \
+    | shsort "vercmp -f $fmt" \
+    | while read dir; do
+        [ "$dir" ] || continue;
+        [ "$dir" != "default" ] || continue;
+
+        if [ "$(vercmp -f "$fmt" "$dir <= $ver")" = "yes" ]; then
+            printf "$HOWROOT/pkg/$pkg/$dir:"
+        fi
+
+    done)$layers"
+fi
+
+[ "$tgt" ] || { echo "$layers$HOWROOT/default" && exit 0; }
+
+# mounting an overlayfs fails if only given a single lower directory, so use a
+# read-only bind mount if just mounting the default scripts directory.  the
+# behaviour of a read-only bind mount should be roughly equivalent to an
+# overlayfs mounted with a single lower directory and no upper directory. (the
+# only difference which comes to mind is that a bind mount does not count
+# against overlayfs' nesting limit.)
+if [ "$layers" ]; then
+    mount -t overlay -o lowerdir="$layers$HOWROOT/default" none "$tgt"
+else
+    mount -o ro,bind "$HOWROOT/default" "$tgt"
+fi

lib/log.sh

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+#!/bin/sh
+
+err() {
+    >&2 echo "[ERR] $1"
+    exit 1
+}
+
+warn() {
+    >&2 echo "[WRN] $1"
+}
+
+log() {
+    echo "[LOG] $1"
+}
+
+debug() {
+    [ -z "$DEBUG" ] || echo "[DBG] $1"
+}

makefile

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+SRCDIR = $(dir $(realpath $(firstword $(MAKEFILE_LIST))))
+PREFIX ?= /usr
+HOWROOT ?= $(PREFIX)/share/how
+DESTDIR ?= $(PREFIX)/bin
+GITBASE ?= $(shell realpath $(shell git config --get remote.origin.url) | rev \
+           | cut -d/ -f2- | rev)
+
+.PHONY: install uninstall lix-os-how
+
+lix-os-how: lix-os-defaults lix-os-pkgs
+
+lix-os-defaults:
+	git clone $(GITBASE)/how-lix-os-defaults default
+
+lix-os-pkgs:
+	git clone $(GITBASE)/how-lix-os-pkgs pkg
+
+install:
+	ln -sf $(SRCDIR) $(HOWROOT)
+	ln -sf $(HOWROOT)/how.sh $(DESTDIR)/how
+
+uninstall:
+	rm $(DESTDIR)/how
+	rm $(HOWROOT)

sloc.sh

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+#!/bin/sh
+
+# find all *.sh files not under `pkg` that are not symbolic links, strip all
+# trailing whitespace, then all leading whitespace, then all lines starting
+# with '#', then all empty lines. then count the remaining lines.
+
+find . -name "*.sh" ! -path "**/pkg/**" ! -path "**/default/**" ! -type l \
+| xargs sed 's/[[:space:]]*$//g; s/^[[:space:]]*//g; s/^#.*$//g; /^$/d' \
+| wc -l - \
+| cut -d' ' -f1
+
+# note that this script's ELOC is also included in the count.