Introduction

       The  unix:  module provides access to features that only make sense on UNIX-like operating
       systems, such as Linux, FreeBSD, and macOS.

       On non-UNIX operating systems, such as MS Windows, this namespace does not exist  and  use
       unix  will  fail.   Use  the  $platform:is-unix variable to determine if this namespace is
       usable.

Variables

   $unix:rlimits {#unix:rlimits}
       A map describing resource limits of the current process.

       Each key is a string corresponds to a resource, and each value is a map with keys &cur and
       &max, describing the soft and hard limits of that resource.  A missing &cur key means that
       there is no soft limit; a missing &max key means that there is no hard limit.

       The following resources are supported, some only present on certain OSes:

       Key          Resource             Unit      OS
       ───────────────────────────────────────────────────────────────
       core         Core file            bytes     all
       cpu          CPU time             seconds   all
       data         Data segment         bytes     all
       fsize        File size            bytes     all
       memlock      Locked memory        bytes     all
       nofile       File descriptors     number    all
       nproc        Processes            number    all
       rss          Resident set size    bytes     all
       stack        Stack segment        bytes     all
       as           Address space        bytes     Linux, Free/NetBSD
       nthr         Threads              number    NetBSD
       sbsize       Socket buffers       bytes     NetBSD
       locks        File locks           number    Linux
       msgqueue     Message queues       bytes     Linux
       nice         20 - nice value                Linux
       rtprio       Real-time priority             Linux
       rttime       Real-time CPU time   seconds   Linux
       sigpending   Signals queued       number    Linux

       For the  exact  semantics  of  each  resource,  see  the  man  page  of  getrlimit:  Linux
       (https://man7.org/linux/man-pages/man2/setrlimit.2.html),                            macOS
       (https://developer.apple.com/library/archive/documentation/System/Conceptual/ManPages_iPhoneOS/man2/getrlimit.2.html),
       FreeBSD            (https://www.freebsd.org/cgi/man.cgi?query=getrlimit),           NetBSD
       (https://man.netbsd.org/getrlimit.2),  OpenBSD  (https://man.openbsd.org/getrlimit.2).   A
       key foo in the Elvish API corresponds to RLIMIT_FOO in the C API.

       Examples:

              ~> put $unix:rlimits
              ▶ [&nofile=[&cur=(num 256)] &fsize=[&] &nproc=[&max=(num 2666) &cur=(num 2666)] &memlock=[&] &cpu=[&] &core=[&cur=(num 0)] &stack=[&max=(num 67092480) &cur=(num 8372224)] &rss=[&] &data=[&]]
              ~> # mimic Bash's "ulimit -a"
              ~> keys $unix:rlimits | order | each {|key|
                   var m = $unix:rlimits[$key]
                   fn get {|k| if (has-key $m $k) { put $m[$k] } else { put unlimited } }
                   printf "%-7v %-9v %-9v\n" $key (get cur) (get max)
                 }
              core    0         unlimited
              cpu     unlimited unlimited
              data    unlimited unlimited
              fsize   unlimited unlimited
              memlock unlimited unlimited
              nofile  256       unlimited
              nproc   2666      2666
              rss     unlimited unlimited
              stack   8372224   67092480
              ~> # Decrease the soft limit on file descriptors
              ~> set unix:rlimits[nofile][cur] = 100
              ~> put $unix:rlimits[nofile]
              ▶ [&cur=(num 100)]
              ~> # Remove the soft limit on file descriptors
              ~> del unix:rlimits[nofile][cur]
              ~> put $unix:rlimits[nofile]
              ▶ [&]

   $unix:umask {#unix:umask}
       The  file  mode creation mask.  Its value is a string in Elvish octal representation; e.g.
       0o027.  This makes it possible to use it in any context that expects a $number.

       When assigning a new value a string is implicitly treated as an  octal  number.   If  that
       fails  the  usual  rules for interpreting numbers are used.  The following are equivalent:
       set unix:umask = 027 and set unix:umask = 0o27.  You can also assign to it a float64  data
       type that has no fractional component.  The assigned value must be within the range [0 ...
       0o777], otherwise the assignment will throw an exception.

       You can do a temporary assignment to  affect  a  single  command;  e.g.   umask=077  touch
       a_file.   After  the command completes the old umask will be restored.  Warning: Since the
       umask applies to the entire process, not individual threads, changing  it  temporarily  in
       this  manner  is  dangerous  if  you are doing anything in parallel, such as via the peach
       command.