On 11/13/18 10:29 AM, Service wrote:
# ensure that file1 exists and that file2 does not exist
There's your problem. It is inherently ambiguous what timestamp to use when a file is missing (infinitely new or infinitely old, or always an error for not existing); bash's -nt picked one way, while other shells have picked the other. POSIX is silent on the matter (-nt is an extension outside of POSIX), so there is nothing portable you can rely on.
/bin/touch file1 /bin/rm -f file2 # built-in if [ file1 -nt file2 ]; then echo nt; else echo not_nt; fi # external if /usr/bin/[ file1 -nt file2 ]; then echo nt; else echo not_nt; fi # Output is as expected: nt nt
That is, bash's builtin '[' and coreutil's external '[' happened to pick the same thing: a missing file is treated as infinitely old.
2. This does not work: # Put the above commands into a script, say check.sh # Run with: /bin/sh < check.sh # Or : /bin/sh ./check.sh # Or : /usr/bin/env ./check.sh # Output is always not ok: not_nt nt
Most likely, this is because your /bin/sh is not bash, but probably dash, and dash has picked a missing file as being treated as always an error. That does not make it a bug in bash, though, but a difference in behavior of your /bin/sh.
-- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3266 Virtualization: qemu.org | libvirt.org
