Validating user input

sachin_mt · #1 (**permalink**) 04-08-04, 09:40

Hi,

I have a shell program which reads user input

read a

now i need to make sure that the variable a will not have special characters like single quote ' or double quote " how can I check this?

can I validate the variable once it is read in a shell program.

aigles · #2 (**permalink**) 04-08-04, 09:56

You can do something like this :

Code:

# With 'if' and 'expr'

if expr "$a" : ".*['\"].*" >/dev/null
   then echo "Variable contains special(s) character(s)"
   else echo "Variable is valid"
fi

# With 'case'

case "$a" in
   *[\\'\"]*) echo "Variable contains special(s) character(s)";;
   *)          echo "Variable is valid" ;;
esac

sachin_mt · #3 (**permalink**) 04-16-04, 07:59

Hi,

I have 2 questions

1.
In this line can you pl. explain why we need this >/dev/null

if expr "$a" : ".*['\"].*" >/dev/null

2.Is it possible to validate more than one variables say $a and $b in a single, if statament

praveenpr · #4 (**permalink**) 04-16-04, 08:51

Quote:

Originally posted by sachin_mt
Hi,

I have 2 questions

1.
In this line can you pl. explain why we need this >/dev/null

if expr "$a" : ".*['\"].*" >/dev/null

2.Is it possible to validate more than one variables say $a and $b in a single, if statament

/dev/null is used to discard the other messages

aigles · #5 (**permalink**) 04-16-04, 10:27

The command 'expr "$a" : ".*['\"].*"' display the length of the matching string. With >/dev/null the display is invisible.

To check variables a and b :

if expr "$a$b" : ".*['\"].*"

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