#!/bin/bash

TAR_FILE="$1"
shift

TMP_ROOT="/dev/shm" # ...or /tmp
TMP_DIR="$(mktemp -d "$TMP_ROOT/xargs-tar-XXXXXX")"
UNTAR_DIR="$TMP_DIR/untar"
FILE_LIST="$TMP_DIR/files-list"
EXEC_FILE="$TMP_DIR/exec-file"

mkdir -p "$UNTAR_DIR"
mkfifo "$FILE_LIST"

(
    # single quotes for user's command and args
    for i in "$@"; do
            echo -n "'$i' "
    done
    echo '"$@"'
    echo 'rm "$@"'
) > "$EXEC_FILE"
chmod u+x "$EXEC_FILE"

# Background untar. Write file list (zero terminated, no directories) to named
# pipe. The output is one line delayed to make sure we print only finished file
# names.
(
    tar -v -C "$UNTAR_DIR" -xf "$TAR_FILE"
            | awk 'BEGIN {last = "";}
                   !//$/ {if (last != "") print last; last=$0;}
                   END {if (last != "") print last;}'
            | tr 'n' ''
) > "$FILE_LIST" &

cd "$UNTAR_DIR"
xargs --null -r sh "$EXEC_FILE" < "$FILE_LIST"

rm -rf "$TMP_DIR"

./xargs-tar  palemoon.tar.bz2  wc -l
      546 palemoon/libsoftokn3.so
     1437 palemoon/libnss3.so
[...]
      267 palemoon/libnssutil3.so
      220 palemoon/libsmime3.so
        6 palemoon/defaults/pref/channel-prefs.js
   379727 total

tar -xf palemoon.tar.bz2
find palemoon -type f -print0 | xargs -0 wc -l
rm -rf palemoon