@node Portability
@section Making @command{tar} Archives More Portable
+@cindex portable archives
Creating a @command{tar} archive on a particular system that is meant to be
useful later on many other machines and with other versions of @command{tar}
is more challenging than you might think. @command{tar} archive formats
@node Reproducibility
@section Making @command{tar} Archives More Reproducible
+@cindex reproducible archives
Sometimes it is important for an archive to be @dfn{reproducible},
so that one can be easily verify it to have been derived solely from
its input. We call an archive reproducible, if an archive
--date=format:%Y-%m-%dT%H:%M:%SZ \
"$@@"
@}
-SOURCE_EPOCH=$(get_commit_time)
+#
+# Set each source file timestamp to that of its latest commit.
git ls-files | while read -r file; do
- commit_time=$(get_commit_time -- "$file") &&
- touch -cmd $commit_time -- "$file"
+ commit_time=$(get_commit_time "$file") &&
+ touch -md $commit_time "$file"
done
+#
+# Set timestamp of each directory under $FILES
+# to the latest timestamp of any descendant.
+find $FILES -depth -type d -exec sh -c \
+ 'touch -r "$0/$(ls -At "$0" | head -n 1)" "$0"' \
+ @{@} ';'
+#
+# Create $ARCHIVE.tgz from $FILES, pretending that
+# the modification time for each newer file
+# is that of the most recent commit of any source file.
+SOURCE_EPOCH=$(get_commit_time)
TARFLAGS="
--sort=name --format=posix
--pax-option=exthdr.name=%d/PaxHeaders/%f
--numeric-owner --owner=0 --group=0
--mode=go+u,go-w
"
-GZIPFLAGS="
- --no-name --best
-"
-LC_ALL=C tar $TARFLAGS -cf - FILES |
- gzip $GZIPFLAGS > ARCHIVE.tgz
+GZIPFLAGS="--no-name --best"
+LC_ALL=C tar $TARFLAGS -cf - $FILES |
+ gzip $GZIPFLAGS > $ARCHIVE.tgz
@end example
@node cpio