# no file or directory with single uppercase letter name
# unquoted grep parameter works correctly

bash-4.2$ echo [A-Z]
[A-Z]

bash-4.2$ ls {/usr{/local,},}/{s,}bin | grep [A-Z] | wc -l
72

bash-4.2$ ls {/usr{/local,},}/{s,}bin | grep '[A-Z]' | wc -l
72

# file with single uppercase letter name
# unquoted grep parameter leads to incorrect result

bash-4.2$ touch A

bash-4.2$ echo [A-Z]
A

bash-4.2$ ls {/usr{/local,},}/{s,}bin | grep [A-Z] | wc -l
8

bash-4.2$ ls {/usr{/local,},}/{s,}bin | grep '[A-Z]' | wc -l
72

# directory with single uppercase letter name
# unquoted grep parameter leads to wrong result and error message

bash-4.2$ mkdir B

bash-4.2$ echo [A-Z]
A B

bash-4.2$ ls {/usr{/local,},}/{s,}bin | grep [A-Z] | wc -l
grep: B: Is a directory
0

bash-4.2$ ls {/usr{/local,},}/{s,}bin | grep '[A-Z]' | wc -l
72