draft to enable pwsh to be used as login shell

2-Draft-Accepted/RFCnnnn-PowerShell-as-Login-Shell.md

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+---
+RFC: RFCnnnn
+Author: Steve Lee
+Status: Draft
+SupercededBy: N/A
+Version: 1.0
+Area: Console
+Comments Due: June 6, 2019
+Plan to implement: Yes
+---
+
+# Enable PowerShell as Login Shell on POSIX-based systems
+
+POSIX shells on Unix-based systems use a `-l` switch to start the shell as a login shell.
+This means the shell is not being started from an existing configured environment and
+needs to execute `/etc/profile` to populate environment variables along with other
+environment changes.
+
+## Motivation
+
+    As a PowerShell user,
+    I can use PowerShell as my login shell on Unix-based systems,
+    so that I can use PowerShell everywhere.
+
+## Specification
+
+Many existing tools expect `-l` to be accepted by a shell and to act as a login
+shell.
+
+`-l` (expanded form is `-LoadProfile`) will explicitly have pwsh load the PowerShell
+profile.
+This is effectively a no-op as if this switch is not specified, pwsh will load
+the PowerShell profile and only doesn't load it if `-noprofile` is specified.
+
+This will allow tools that expect `-l` to be accepted to work.
+There is no additional work to process `/etc/profile` when `-l` is used.
+
+For cases where you do need `/etc/profile` to be processed,
+such as using pwsh as your default shell,
+the proposal is to include a Bourne shell script that can be specified as the
+shell:
+
+```sh
+#!/bin/sh -l
+exec /usr/local/bin/pwsh "$@"
+```
+
+This script will be called `pwsh-login` and should be used whenever you require
+a specific login shell.
+
+## Alternate Proposals and Considerations
+
+### Process /etc/profile using sh and copy the env vars
+
+This proposal would be that if `-l` is specified, pwsh would run `/bin/sh -l -c export`
+which would create a new shell process that does all the processing needed for
+a login shell and export the environment variables that would be exported.
+Additional code is needed to take those environment variables and copy them to
+the parent pwsh process.
+
+The downsides to this approach is additional code to maintain,
+but more importantly not getting a complete login shell environment as things
+like ulimit and umask would not be inherited into pwsh.
+
+### pwsh to start `/bin/sh -l -c "exec pwsh"`
+
+This proposal would have pwsh when given the `-l` switch to start Bourne shell
+as a login shell and start pwsh within that process.
+
+This would result in a complete login shell environment, however, would
+incur the performance penalty of starting pwsh twice.