It can be useful to retrieve information about a Mac from the command line. For example, if you have booted into recovery mode or to an installer, or you have done a remote SSH session to another computer.
This command shows piles of stuff, but is slow: system_profiler
Shows lots of system paramaters, fast: sysctl -a
Show running OS version: sw_vers
Show OS version on disk: cat /Volumes/Macintosh\ HD/System/Library/CoreServices/SystemVersion.plist. Note: Assumes disk is called "Macintosh HD".
Show free space on volumes: df -H
Show model number only: system_profiler SPHardwareDataType | grep 'Model Identifier'
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