applets_sh/*: Add a few more examples of "shell applets"

Signed-off-by: Pere Orga <gotrunks@gmail.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

applets_sh/README

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+This directory contains examples of applets implemented as shell scripts.
+
+So far these scripts are not hooked to the build system and are not
+installed by "make install". If you want to use them,
+you need to install them by hand.

applets_sh/dos2unix

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+#!/bin/sh
+# TODO: use getopt to avoid parsing options as filenames,
+# and to support -- and --help
+[ $# -ne 0 ] && DASH_I=-i
+sed $DASH_I -e 's/\r$//' "$@"

applets_sh/tac

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+#!/bin/sh
+# TODO: use getopt to avoid parsing options as filenames,
+# and to support -- and --help
+for i in "$@"
+do
+sed -e '1!G;h;$!d' "$i"
+done

applets_sh/unix2dos

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+#!/bin/sh
+# TODO: use getopt to avoid parsing options as filenames,
+# and to support -- and --help
+[ $# -ne 0 ] && DASH_I=-i
+sed $DASH_I -e 's/$/\r/' "$@"