Implement ulimit builtin

[jyn514]

Found this while investigating #279 - we don't implement ulimit. There's a man page at https://ss64.com/bash/ulimit.html, strace shows that bash is using prlimit64. Python has this in a library: https://docs.python.org/3.5/library/resource.html#resource.prlimit

$ ulimit -u
prlimit64(0, RLIMIT_NPROC, NULL, {rlim_cur=1000, rlim_max=1000}) = 0
write(1, "1000\n", 5)
$ ulimit -u 999
prlimit64(0, RLIMIT_NPROC, NULL, {rlim_cur=1000, rlim_max=1000}) = 0
prlimit64(0, RLIMIT_NPROC, {rlim_cur=999, rlim_max=999}, NULL) = 0

[andychu]

Yes good point. This would be a great contribution for someone since it's self-contained and AFAIK is a wrapper for the syscall :)

It may have side effects that aren't easily testable, but in those cases I think simply testing that it "doesn't crash" is fine first the first pass. I also sometimes add manual demos in demo/.

[andychu]

Another user hit this in #161

https://gist.github.com/wertercatt/5820fe28f9e107a55d6f28929c919c8f

@wertercatt

[gardenappl]

Found this during Java development: gradlew uses ulimit.

Osh prints an error, but apparently the gradlew script can handle this, so it just shows "Could not query maximum file descriptor limit" and keeps on going.

[kseistrup]

As of Oils 0.21.0 (commit cc2f683) the ulimit command is still missing:

$ osh -c 'ulimit -n 1024'
  ulimit -n 1024
  ^~~~~~
[ -c flag ]:1: 'ulimit' not found

bash scripts that attempt to use ulimit will fail.

[kseistrup]

PS: See also #1914

[andychu]

Released - https://www.oilshell.org/blog/2024/06/release-0.22.0.html