Command aliases in my script - linux

Question

I am creating a script for copying files or directory with a date attached to its name, for example if the file name is test it will be test-20130901.bkup
and this is my script
#!/usr/bin/bash
set -x
getopts fd TYPE
[ $TYPE = "d" ] && alias cp="cp -r"
backup_error() {
echo "${0##*/}: $1"
exit -1
}
typeset -r FROM_DIR=$2 TO_DIR=$3
if [ ! -e $FROM_DIR -a ! -d $FROM_DIR ] || [ ! -e $TO_DIR -a ! -d $TO_DIR ]
then
backup_error "One of the directories isn't exist or it maybe a file";
fi
typeset -r DATE=$(date "+%Y%m%d")
for filename in $FROM_DIR/*
do
if [ -$TYPE $filename ]
then
cp $filename $TO_DIR/${filename##*/}-$DATE.bkup
fi
done
unalias cp
In the script I check if the user wants to run the script on files only or on directories only.
-f for files only
-d for directories only
[ $TYPE = "d" ] && alias cp="cp -r", this line to check if the script runs for directory I must use cp -r so I make an alias for cp to be cp -r
but when I use set -x to debug I find the when a user use -d option the cp command in the if still the original one not the alias.
Debugging:
> ./backup.sh -d . .
+ getopts fdb TYPE
+ '[' d = d ']'
+ alias 'cp=cp -r'
+ typeset -r FROM_DIR=. TO_DIR=.
+ '[' '!' -e . -a '!' -d . ']'
+ '[' '!' -e . -a '!' -d . ']'
++ date +%Y%m%d
+ typeset -r DATE=20130901
+ '[' -d ./backup.sh ']'
+ '[' -d ./dir1 ']'
+ cp ./dir1 ./dir1-20130901.bkup
cp: ./dir1: is a directory
+ '[' -d ./file1 ']'
+ '[' -d ./file2 ']'
+ '[' -d ./test.sh ']'
+ unalias cp

Answer 1

Use a function instead:
if [[ $TYPE == d ]]; then
function cp {
command cp -r "$#"
}
fi
And when in Bash, [[ ]] is recommended over test or [ ].
Also quote please quote your variables properly between "" to prevent word splitting and unexpected pathname expansion.
Other caveats:
exit -1 ## exit can only accept 8-bit integral values from 0 to 255. -1 here is orthodox and is equivalent to 255.
You should quote the variables here or use [[ ]]:
if [[ ! -e $FROM_DIR && ! -d $FROM_DIR ]] || [[ ! -e $TO_DIR && ! -d $TO_DIR ]]
if [ "-$TYPE" "$filename" ] ## for custom operators, test is better: test "-$TYPE" "$filename"
cp "$filename" "$TO_DIR/${filename##*/}-$DATE.bkup"
for filename in "$FROM_DIR"/*
Lastly make sure you run your script as:
bash script.sh -f from_dir to_dir
# Or
bash script.sh -d from_dir to_dir