why the perl one-liner not run with variable input files

Have the following code block
set WKDIR=D:\TEMP\
set _out1=%WKDIR%\test2.txt
set _in1=%WKDIR%\test1.txt
perl -lne "$lines{ $_ }++; END{ print for sort keys %lines }"  %_in1% > %_out1%
I got the error:
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Missing right curly or square bracket at -e line 1, at end of line
syntax error at -e line 1, at EOF
Execution of -e aborted due to compilation errors.
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but when I did the following
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d:
cd D:\TEMP
perl -lne "$lines{ $_ }++; END{ print for sort keys %lines }"  test1.txt > test2.txt
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I can get the right result without errors.
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D:\TEMP>type test1.txt
WWW
AB_C
ABB
ACB
ABB
XYZ
123
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