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Ommiting special characters as input - Help

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# 1  
Old 11-17-2010
Ommiting special characters as input - Help
Hey Everyone,

I'm quite new to unix (hence the 0 posts!) and im trying to write a simple program that outputs what the user types in to the screen, as long as it is a letter.

This part works fine, however, when a "\" is entered doesnt not display anything and moves to the next line. Is there any way to display an error message when a backslash/or special characters are entered?

thanks in advance everyone
# 2  
Old 11-17-2010
Please show us your code...
# 3  
Old 11-17-2010
Code:
 
#!/bin/bash
 
echo "enter a letter"
read letter
echo $letter
 
lettercheck=$(echo "$letter" | grep [a-zA-Z])
 
                if [ -z $letter ] #checks if length of string is zero
                then
                        echo "Invalid input. Input is not a letter"
                        
                else
                        echo $letter
 
        fi

thats pretty much it. the code works fine, but when a "\" is entered it just moves onto the next line rather than checking the input at all.
# 4  
Old 11-17-2010
You need to test $lettercheck not $letter.


Code:
                if [ -z "${lettercheck}" ] #checks if length of string is zero


And try "read -r" to deal with the reverse solidus character (which has special meaning to the Shell).

Code:
read -r letter

Last edited by methyl; 11-17-2010 at 07:50 AM.. Reason: And ...
# 5  
Old 11-17-2010
thanks a lot methyl!

in my original code I was checking the right variable by I retyped an easier version of what I was doing and forgot to change it.



read -r was exactly was I was looking for so thanks a lot!!
# 6  
Old 11-17-2010
Or use:
bash code:
  1. if [[ $letter == [[:alpha:]] ]]; then
  2.   echo $letter
  3.  else
  4.   echo "Invalid input. Input is not a letter"
  5. fi

or use:
shell code:
  1. case $letter in  
  2.   [[:alpha:]]) echo $letter ;; 
  3.   *) "Invalid input. Input is not a letter" ;;
  4. esac
Last edited by Scrutinizer; 11-17-2010 at 08:31 AM..
# 7  
Old 11-17-2010
cheers for the input scrutinizer. however, the problem was that if you enter "\" then without -r it doesnt actually get to any of your checks, as it reads the "\" as an escape character and does nothing.

thanks!
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