Checking input is Numerical

gregarion · 01-18-2010, 01:56 PM

Hey guys, what i am trying to do is to allow the user to key in data , such as "23.23" or "24" , as it is the price of certain objects

How am i able to design a check which will allow me to prevent users from typing in input such as "ab.21" or "rfrr" as this field is purely a numerical field.

The problem i am facing is i tried using this search code.

Code:

echo "read this"
read this
if [ -z "`echo "$this" | tr -d  [[:digit:]]`" ] ;

echo "True - only  numeric"
else
echo "False - there are NON a numeric stuff here!"
fi

when i enter "1" or "a" for input, it will read the correct statements. but when i try inputting data such as "1.32" , it will give me a message saying "False - there are NON a numeric stuff here!". i can change the option to [[:alnum:]] , but then that would allow entries such as "aa.21" to be accepted.

Anybody knows how i can deal with this problem?

devnull10 · 01-18-2010, 02:09 PM

Try the following regular expression:

Code:

[0-9]+\.?[0-9]*

Disillusionist · 01-18-2010, 02:23 PM

Quote:

Originally Posted by gregarion

Code:

echo "read this"
read this
if [ -z "`echo "$this" | tr -d  [.[:digit:]]`" ]
then
   echo "True - only  numeric"
else
   echo "False - there are NON a numeric stuff here!"
fi

include a full stop before the [:digit:]

gregarion · 01-19-2010, 07:56 AM

Just to check. the code works by first echoing $this, and then deleting it only if the char in the "$this" is numerical or digit?

konsolebox · 01-19-2010, 08:02 AM

in bash it can be done this way:

Code:

shopt -s extglob

echo "read this"
read this

if [[ $this == +([[:digit:]]) ]]; then    # +([[:digit:]])?(.+([[:digit:]]))
    echo "True - only  numeric"
else
    echo "False - there are NON a numeric stuff here!"
fi

Sergei Steshenko · 01-19-2010, 08:03 AM

Quote:

Originally Posted by devnull10

Try the following regular expression:

Code:

[0-9]+\.?[0-9]*

And what about scientific notation, i.e. 1.23e45 ? Or the OP doesn't need it ?

gregarion · 01-19-2010, 08:14 AM

Nopes, it does not need scientific notation. Its just used to enter decimals meant for price of an object.

Sorry Konsolebox , but can i check why does "+([[:digit:]])" need an extra () and + infront of it? and what does "shopt -s extglob" do?

i tried running it like this :

Code:

#!/bin/bash



echo "read this"
read this

if [[ $this == +([[:digit:]]) ]]; then    # +([[:digit:]])?(.+([[:digit:]]))
    echo "True - only  numeric"
else
    echo "False - there are NON a numeric stuff here!"
fi

and i got this error message.

Code:

./test: line 8: syntax error in conditional expression: unexpected token `('
./test: line 8: syntax error near `+(['
./test: line 8: `if [[ $this == +([[:digit:]]) ]]; then    # +([[:digit:]])?(.+([[:digit:]]))'

is it due the fact i did not put in "shopt -s extglob"?

konsolebox · 01-19-2010, 08:27 AM

Quote:

Originally Posted by gregarion

is it due the fact i did not put in "shopt -s extglob"?

Yes. It enables extended globbing. Perhaps we can also do that we regex:

Code:

[[ $this =~ [[:digit:]]+(\.[[:digit:]]+)? ]] ...

Sorry I don't have access to a terminal to try this.

gregarion · 01-19-2010, 08:32 AM

Hey thanks again konsolebox , but just to check with u about the code below

Code:

if [ -z $( echo "$this" | tr -d '[.[:digit:]]') ] ;

Code:

Code:

echo "$this" |

*this echo out the content inside $this and pipes it into the next set of command

Code:

Code:

tr -d '[.[:digit:]]')

*this command will check if the data from the $this is in digits and has a "." , and if it is, will delete them. if not, it will not delete them , thus the data will not be 0 and this the message that there is a non-numeric stuff is inside.

did i get it right?

konsolebox · 01-19-2010, 08:47 AM

I see nothing wrong with it but perhaps you need to quote $()?

Code:

if [ -z "$( echo "$this" | tr -d '[.[:digit:]]')" ]

You won't need it though if you're using '[[':

Code:

if [[ -z $(...) ]]; ...

Also I think that method is a bit.. dangerous or.. not reliable? It's even better if you just use grep:

Code:

 if echo "$this" | grep "^[[:digit:]]\+$" > /dev/null; then ...

gregarion · 01-19-2010, 09:15 AM

Lol, yeah, i am using the grep method, but i was asking about the other coding because i was curious about how it work for my general knowledge? is my explanation for it correct?

ghostdog74 · 01-19-2010, 10:54 PM

Code:

awk 'BEGIN{
    printf "Read this: "
    getline this <"-"
    if ( this+0==this ){
        print "Ok"
    }else{
        print "Not ok"
    }
}'

output

Code:

$ ./shell.sh
Read this: 32121
Ok

$ ./shell.sh
Read this: .033
Ok

$ ./shell.sh
Read this: 231.cb
Not ok

gregarion · 01-19-2010, 11:27 PM

Could you explain how it works? i do not get the part +0?

ghostdog74 · 01-19-2010, 11:39 PM

Quote:

Originally Posted by gregarion

Could you explain how it works? i do not get the part +0?

this+0 converts it to integer(number)

konsolebox · 01-20-2010, 08:12 PM

An invalid input like this can also make a match.

Code:

this="1.2.3.4....."
echo "$this" | tr -d '[.[:digit:]]'

It's really better if you just use grep or any other than tr.