Here is what I"m getting, and I can’t apparently use discard? I got it from win64 prerelease.
C:\Windows\System32>gmic 21,1,1,3,perm(c+2,x+5,0) unroll x sort x discard x .
[gmic]./ Start G'MIC interpreter (v.3.5.0).
[gmic]./ Input image at position 0, with values 'perm(c+2,x+5,0)' (1 image 21x1x1x3).
[gmic]./ Unroll image [0] along the 'x'-axis.
[gmic]./ Sort values of image [0] in ascending order.
[gmic]./ Execute external command 'discard' in verbose mode.
'discard' is not recognized as an internal or external command,
operable program or batch file.
[gmic]./ Command 'exec' returned error code 1.
[gmic]./ Execute external command '.' in verbose mode.
'.' is not recognized as an internal or external command,
operable program or batch file.
[gmic]./ Command 'exec' returned error code 1.
[gmic]./ Display image [0] = '[perm(c+2,x+5,0)]'.
[0] = '[perm(c+2,x+5,0)]':
size = (63,1,1,1) [252 b of float32].
data = (5,10,10,15,15,20,21,28,35,35,36,45,55,56,66,70,78,84,91,105,120,120,126,136,153,165,171,190,210,210,220,231,253,276,286,300,330,364,455,495,560,680,715,816,969,1001,1140,1330,1365,1540,1771,1820,2024,2300,2380,3060,3876,4845,5985,7315,8855,10626,12650).
min = 5, max = 12650, mean = 1322.44, std = 2579.34, coords_min = (0,0,0,0), coords_max = (62,0,0,0).
[gmic]./ End G'MIC interpreter