chore(kb): get users' login shell

knowledge base/get users' login shell.md

@@ -0,0 +1,48 @@
+# Get users' login shell
+
+1. [TL;DR](#tldr)
+1. [Further readings](#further-readings)
+   1. [Sources](#sources)
+
+## TL;DR
+
+```sh
+# Works on Linux and Mac OS X.
+# Tested with BASH, CSH, DASH, FISH, KSH, TCSH and ZSH.
+finger "$USER" | grep 'Shell:' | awk '{print $NF}'
+
+# Works on Linux.
+# Tested with BASH.
+getent passwd "$USER" | awk -F ':' '{print $NF}'
+getent passwd "$USER" | cut -d ':' -f '7'
+
+# Works on Linux.
+# Does *not* work on Mac OS X because it uses Apple's OpenDirectory and only
+# refers to '/etc/passwd' or '/private/etc/passwd' when in single user mode.
+# Tested with BASH.
+grep "$USER" '/etc/passwd' | awk -F ':' '{print $NF}'
+grep "$USER" '/etc/passwd' | cut -d ':' -f '7'
+
+# Works on Mac OS X.
+# Does *not* work on systems without OpenDirectory.
+# Tested with BASH, CSH, DASH, FISH, KSH, TCSH and ZSH.
+dscl '.' -read "/Users/$USER" 'UserShell' | awk '{print $NF}'
+dscl '.' -read "/Users/$USER" 'UserShell' | cut -d ' ' -f '2'
+```
+
+## Further readings
+
+### Sources
+
+- [Users don't appear in /etc/passwd on Mac OS X]
+
+<!--
+  References
+  -->
+
+<!-- In-article sections -->
+<!-- Knowledge base -->
+<!-- Files -->
+<!-- Upstream -->
+<!-- Others -->
+[users don't appear in /etc/passwd on mac os x]: https://superuser.com/questions/191330/users-dont-appear-in-etc-passwd-on-mac-os-x#1425510

knowledge base/mac os x/README.md

@@ -142,6 +142,10 @@ launchctl stop 'job_label'
 
 # Enable file trimming on SSD.
 sudo trimforce enable
+
+
+# Get information about users.
+dscl '.' -read "/Users/$USER" 'UserShell'
 ```
 
 ## Hidden settings