k is not a standard command in Linux.

The Linux Foundation hosts workgroups where individuals can collaborate to solve complex issues facing the Linux platform. The work of many of these workgroups may eventually become best practice and codified into the Linux Standard Base and/or may be submitted as patches to the mainline kernel tree or other packages. Participation is open to all.

ofcourse they are !

most of hem are linux base.

Standard error -- stderr

read, write, execute