help for "read" command

mirzasoltan · 09-09-2013, 06:03 AM

hi everyone,
i am writting a script that i want to get a value (that must be just digits) and do something after that. i used "read" command to get that value, like this:

read -p "please type your number: " N

now i want to check that $N is a number not text and it is only 4 digits not less and not more like digits of a year like "2013".

how i can check this part, or is read command have a switch to accept just digits not alphabets?!

druuna · 09-09-2013, 06:24 AM

Have a look at this:

Code:

read -p "please type your number: " N

if [[ "$N" =~ ^[0-9]{4}$ ]]
then
  echo "Yep, a 4 digit number."
else
  echo "not a 4 digit number."
fi

Too my knowledge read doesn't have an option that forces numerical input.

grail · 09-09-2013, 07:01 AM

Of course to ask more than once as they may make several mistakes you could try:

Code:

while read -p "Enter a number: " N && [[ ! $N =~ ^[0-9]{4}$ ]];do echo "try again";done

The other thing to consider is, what constitutes a number, ie what if they enter 0023

Whilst druuna is correct about read, you could tell bash that the variable is expecting an integer with:

Code:

declare -i N

This will return 0 for alpha starting strings but unfortunately blows up if it starts with a number and then contains alphas
and you would still need to test 4 digit boundary with >999 <10000

mirzasoltan · 09-09-2013, 08:50 AM

Quote:

Originally Posted by druuna

Have a look at this:

Code:

read -p "please type your number: " N

if [[ "$N" =~ ^[0-9]{4}$ ]]
then
  echo "Yep, a 4 digit number."
else
  echo "not a 4 digit number."
fi

Too my knowledge read doesn't have an options that forces numerical input.

tanx man, you hit the point.

druuna · 09-09-2013, 11:56 AM

You're welcome

BTW: Can you put up the [SOLVED] tag (link in top right hand corner or use the Thread Tools menu)