HP-UX

I cannot explain why it gives different results when I try the awk, sed, tr command combination with the same input.
(aondufd1)psoftfs:/aon/dev/psoft/FSTST88/autosys>echo ${MailFile}
+ echo mfint003pr.in1*
mfint003pr.in1*
(aondufd1)psoftfs:/aon/dev/psoft/FSTST88/autosys/scripts>echo ${MailFile} | awk -F. '{ print $1 "." }' | sed 's/.*\(...\)\..*/\1/' | tr [A-Z] [a-z] | tr -d [0-9]
+ echo mfint003pr.in1*
+ awk -F. { print $1 "." }
+ sed s/.*\(...\)\..*/\1/
+ tr -d 1
+ tr [A-Z] a
3pr
(aondufd1)psoftfs:/aon/dev/psoft/FSTST88/autosys/scripts>cd ../parm
+ cd ../parm
(aondufd1)psoftfs:/aon/dev/psoft/FSTST88/autosys/parm>echo ${MailFile} | awk -F. '{ print $1 "." }' | sed 's/.*\(...\)\..*/\1/' | tr [A-Z] [a-z] | tr -d [0-9]
+ echo mfint003pr.in1*
+ awk -F. { print $1 "." }
+ sed s/.*\(...\)\..*/\1/
+ tr -d [0-9]
+ tr [A-Z] [a-z]
pr
One big question mark in my head right now. Could someone please help. Thanks.
There were no additional profiles loaded when changing directories. just doing the cd command.
The output should be 3pr. That would be the correct one, right?

You have a file named "1" in the first directory and you are not quoting the arguments to tr, so "[0-9]" is expanded by the shell to "1".

that is genius! yup I have file named 1 in the first directory. Yes, that is our resolution, to put double quotes for "[0-9]" and to "[A-Z]" "[a-z]". Just a stupid question:
1. How does tr read the file named 1, but I know the tr only accepts strings and characters. I tried to create a file named 3, and it accepts the 1 and 3 files and went to syntax error. how does it happens?
(aondufd1)acking:/aon/dev/psoft/FSTST88/autosys/parm>echo ${MailFile} | awk -F. '{ print $1 "." }' | sed 's/.*\(...\)\..*/>
+ echo mfint003pr.in1*
+ awk -F. { print $1 "." }
+ sed s/.*\(...\)\..*/\1/
+ tr -d 2 3
+ tr [A-Z] [a-z]
tr: The combination of options and String parameters is not legal.
Usage: tr [ -c | -cds | -cs | -ds | -s ] [-A] String1 String2
tr [ -cd | -cs | -d | -s ] [-A] String1