/usr/share/games/spring/selectkeys.txt is in spring-common 85.0+dfsg1-2ubuntu1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 | Control_A AllMap++_ClearSelection_SelectAll+
Control_B AllMap+_Builder_Idle+_ClearSelection_SelectOne+
Control_C AllMap+_ManualFireUnit+_ClearSelection_SelectOne+
Control_R AllMap+_Radar+_ClearSelection_SelectAll+
Control_V AllMap+_Not_Builder_Not_Commander_InPrevSel_Not_InHotkeyGroup+_SelectAll+
Control_W AllMap+_Not_Aircraft_Weapons+_ClearSelection_SelectAll+
Control_X AllMap+_InPrevSel_Not_InHotkeyGroup+_SelectAll+
Control_Z AllMap+_InPrevSel+_ClearSelection_SelectAll+
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