The toolbox rpm readline-8.1-1.aix6.1.ppc.rpm has a minor issue with its post install scriptlet - it is assuming the path of the 'uname' program. 
On update/install/reinstall of readline, when 'coreutils' RPM is also installed, the uname error is repeated 295 times:
Running scriptlet: readline-8.1-1.ppc 2/2
uname: invalid option -- 'W'
Try 'uname --help' for more information.
uname: invalid option -- 'W'
Try 'uname --help' for more information.
...
...
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When coreutils RPM is installed, it includes the open source uname program in /opt/freeware/bin/uname, which does not have the "-W" option that the AIX provided /usr/bin/uname has, and the installer seems to be using. It seems that the readline scriptlet is prioritising the /opt/freeware/bin path before /usr/bin.
AIX uname:
# /usr/bin/uname -W
0
Coreutils uname:
# /opt/freeware/bin/uname -W
/opt/freeware/bin/uname: invalid option -- 'W'
Try '/opt/freeware/bin/uname --help' for more information.
I think the readline RPM is installing OK - it probably just needs to have the uname path hardcoded to /usr/bin/ in its scriptlet. 
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Alan
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