How to check if input is white space and null or not?

Question

This is a sample bash as you see in two ways:

1)First

#!/bin/bash

number=0
echo "Your number is: $number"
IFS=' ' read -t 2 -p "Press space to add one to your number: " input

if [ "$input" -eq $IFS ]; then  #OR ==> if [ "$input" -eq ' ' ]; then
    let number=number+1
    echo $number
else
    echo wrong
fi

2)Second:

#!/bin/bash

number=0
echo "Your number is: $number"
read -t 2 -p "Press space to add one to your number: " input

case "$input" in  
    *\ * )
        let number=$((number+1))
        echo $number
        ;;
    *)
        echo "no match"
        ;;
esac

Now the question:

With these two ways, how can I check if the input parameter is white space or null?

I want to check both white space or null in bash.

Thanks

Space is not an integer. Change -eq with = to compare variable with space to $IFS. — jaypal singh
– jaypal singh, Commented Feb 22, 2014 at 6:02
I want to know if it is null number doesn't change the value..but if it is white space number increases — MLSC
– MLSC, Commented Feb 22, 2014 at 6:05
@MortezaLSC There's no difference for string comparisons. Bourne shell supports = and Bash supports ==. But they are synonymous in bash. — jaypal singh
– jaypal singh, Commented Feb 22, 2014 at 6:06

jaypal singh · Accepted Answer · 2014-02-22 07:14:24Z

2

You can try something like this:

#!/bin/bash

number=0
echo "Your number is: $number"
IFS= read -t 2 -p "Press space to add one to your number: " input
# Check for Space
if [[ $input =~ \ + ]]; then
    echo "space found"
    let number=number+1
    echo "$number"
# Check if input is NULL
elif [[ -z "$input" ]]; then
    echo "input is NULL"
fi

answered Feb 22, 2014 at 7:14

jaypal singh

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2 Comments

jaypal singh Over a year ago

Can you elaborate as to what didn't work? I tested it on my system.

Aleks-Daniel Jakimenko-A. Over a year ago

why not just ((number++)) ? Also you are not checking for all whitespace characters, only the regular space. You can use this [[ $input = *+([[:space:]])* ]] check with extglob instead. Or this regex [[ $input =~ [[:space:]]+ ]]. But it also could be that you only want regular space.

MelBurslan · Accepted Answer · 2014-02-22 06:42:43Z

0

This portion checks if the input string is NULL

if [ "##"${input}"##" = "####" ]
then
echo "You have input a NULL string" 
fi

and this portion checks if one or more white space caharacters were input

newinput=$(echo ${input} | tr -s " ")  # There was a typo on thjis line. should be fixed now
if [ "##"${newinput}"##" = "## ##" ]
then
echo "You have input one (or more) whitespace character(s)" 
fi

combine them in aorder you see fit and set flags in if -- fi blocks to evaluate after you complete all comparisons.

edited Feb 22, 2014 at 6:42

answered Feb 22, 2014 at 6:33

MelBurslan

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5 Comments

MLSC Over a year ago

I tested it, but the error has occured:unexpected EOF while looking for matching `}' ./j.sh: line 15: syntax error: unexpected end of file

MelBurslan Over a year ago

sorry.. I made a typographical error. Please see the first line, marked in the 2nd portion.

MLSC Over a year ago

It has no error but doesn't work properly..let me update my post by your solution..the see it

MelBurslan Over a year ago

when you run my version of the script and hit space then hit enter, what do you get? "1" or "wrong"

MelBurslan Over a year ago

I noticed, you are specifying a 2 second time interval for the user to enter his/her input, but no string length. try echo "Press space to add one to your number: "; read -n 1 input instead of your input line

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