This condition will not work. $letter < "Z" . How can we use numeric comparisons with Alphabets.?
You are mistaken. That is a string comparison. The "integer expression expected" error message came from a non-integer value in $letter when evaluating "[ $letter -eq 0 ]".
needs to be in bash i believe. Im not to sure as our lecturer or tutor hasnt specified this POSIX term. And in the lecture slide > and < can be used to compare string values apparently.
this is what i got so far
Code:
"3")
letter="Z"
if [ $letter \< "Z" && $letter \> "A" ]; then
while [ "$letter" == Z ] || [ "$letter" \< Z ] && [ "$letter" -ne 0 ]; d
o
read letter2
if [ $letter2 \< $letter ]; then
letter=letter2
else
break
fi
done
elif [ $letter2 -eq 0 ]; then
echo Lowest letter is $letter
else
echo "Invalid input. Please enter A-Z (capital) one at a time finalised by a 0"
fi
;;
first line is line 46
i get the following errors atm
Code:
./Assignment4.SH: line 48: [: missing `]'
./Assignment4.SH: line 57: [: -eq: unary operator expected
Invalid input. Please enter A-Z (capital) one at a time finalised by a 0
if [ $letter \< "Z" && $letter \> "A" ]; then ----> ./Assignment4.SH: line 48: [: missing `]'
The "&&" terminates the "[" command. That's why you are seeing the "missing ']'" error.
Code:
elif [ $letter2 -eq 0 ]; then ----> ./Assignment4.SH: line 57: [: -eq: unary operator expected
$letter2 is empty. Since it's unquoted, there's nothing being passed to [ at that spot. The first thing [ sees is -eq, so it complains about wanting a unary operator because it is missing the first operand. You need to double quote your variables to ensure that if they are empty an empty string is passed in their place.
Ok. Then you can use "[[ ... ]]" construction. Inside brackets you can use < and > without backslashes for string comparisons and &&, || as boolean operator without additional brackets. So:
Code:
if [[ "$letter" < Z && "$letter" > A ]]; then
Code:
while [[ "$letter" == Z || "$letter" < Z && "$letter" != 0 ]];
Code:
if [[ "$letter2" < "$letter" ]]; then
Code:
[[ "$letter2" == 0 ]]
1. It's a very good habit to use double quotes around variables. Sometimes you must not use them but it is the special case - when a variable emulates an array.
2. And you don't need use quotes around "barewords" - in shell everything is strings. You can but you shouldn't because of
3. Your 0 is a string really and you don't perform any arithmetic operations. So just use bash string comparison operators: "<" ">" "!=" and "==". And if you want to use quotes around string literal, then use them around zero too (but you really shouldn't - it's just leads to confusion).
4. Double quotes around variables are not to convert them to strings but just save possible spaces inside their values.
I was no aware i could take out backslashes in double bracket instances thats amazing, and treating numbers as strings is something i thought was ok only in java hahahah. Thanks a lot guys. Now that is done i get no errors.
EXCEPT
Now when i try to launch the script it goes straight to the error code i written out to catch out any unwanted inputs. What have i done wrong?
EDIT: Oh i see it Z is not less then the Z i placed. Is there a way to make less then and equal too? like =>? something like le or ge
if [[ "$letter" < Z || "$letter" == Z && "$letter" > A || "$letter" == A ]]; then
EDIT:
Code:
"3")
clear
echo Enter capitol alphabetical letters one at a time and press 0 to finish
letter="Z"
if [[ "$letter" < Z || "$letter" == Z ]] && [[ "$letter" > A || "$letter" == A ]]; then
while [[ "$letter" == Z || "$letter" < Z ]] && [[ "$letter" > A || "$letter" == A ]] && [[ "$letter" != 0 ]]; do
read letter2
if [[ $letter2 < $letter ]]; then
letter=letter2
else
break
fi
break
done
elif [ "$letter2" == 0 ]; then
echo Lowest letter is $letter
else
echo "Invalid input. Please enter A-Z (capital) one at a time finalised by a 0"
fi
;;
ive changed the code a bit more to make it like this. No errors occurs. However when i run the script it will ask for input and afterwards break out of all loops and end the program returning to the menu. What have i done wrong?
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