Compatibility of the Zig build with the shell script

The Zig build (0.2.x) keeps the shell script’s (0.1.0) interface. The shell script stays in the repository as the reference: tests/test_eb_keep_logs.sh runs against either through TOOL_BIN, and tests/differential.sh runs both on the same invocations.

Kept

commands	failed STATUS NAME LOGDIR [TMP_LOGDIR], rotate ROOT --compress-after DAYS [--delete-after DAYS], -h, --help, --version
exit codes	0 on success and on every failed that got past its arguments; 2 for a refused invocation, after eb-keep-logs: MESSAGE on stderr; 2 with the usage text on stdout for no arguments
environment	PATH (finds eb), EASYBUILD_TMPDIR, EB_KEEP_LOGS_NOW, TZ, TZDIR
stdout	Failed build log: LOGDIR/NAME.failed.ebout.log, Failed command output: LOGDIR/NAME.failed.command-{out,err}.txt, Failed meson test log: LOGDIR/NAME.failed.meson-testlog.txt, No EasyBuild log to keep for NAME., eb-keep-logs rotate: N files compressed, M runs deleted under ROOT
files	kept files closed to others (command streams mode 0600), their resolved paths appended to LOGDIR/.licensed-logs; rotate writes FILE.gz with the file’s mode and updates .licensed-logs to the .gz path
run ages	days from the local midnight of the date in the run’s name, as date -d YYYYMMDD computes it, including TZ rules; a run whose local midnight does not exist is skipped

Deliberate differences

case	shell script	Zig build
no arguments, --help	prints a trailing half sentence from the script’s header	stops after the --version line
--version	eb-keep-logs 0.1.0	eb-keep-logs 0.2.1 (TARGET, MODE, zig VERSION, COMMIT); the first two words are unchanged
--compress-after or --delete-after with no value after it	never returns	refused, exit 2
EB_KEEP_LOGS_NOW not an integer	evaluated as shell arithmetic	refused, exit 2
a copy into LOGDIR fails	error from cp, then the file is still listed and reported	error on stderr; the file is neither listed nor reported
a symbolic link or non-regular file at a destination name in LOGDIR	cp writes through it	refused, reported on stderr
the failing command’s streams	checked by path (realpath, -L, stat), then copied	opened without following a symbolic link at the last component; the same checks run on the open file, and that file is copied
.licensed-logs after rotate	rewritten by every compressed file, as a new file owned by the caller	rewritten once per run when a line changes, keeping its owner (when permitted), mode and access ACL (access control list) entries, replaced atomically
a run directory that cannot be removed	counted as deleted	reported on stderr, not counted
compression	runs gzip -9, find and awk	in process; the gzip header (name, mtime, flags, OS) matches gzip -9, the compressed bytes differ; a file with other hard links or an existing .gz is skipped as gzip skips it
eb --last-log that does not return	waits without a limit	its process group is killed after 300 s, and nothing is kept
a log larger than 1 GiB	scanned	copied, not scanned for the command output or meson paths, with a message on stderr
a log with NUL bytes	grep reports a binary match and the scan finds nothing	scanned as text