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, Feb 22 '14 at 06:02
http://stackoverflow.com/questions/13509508/check-if-string-is-neither-empty-not-space-in-shell-script — Shivam, Feb 22 '14 at 06:03
I want to know if it is null number doesn't change the value..but if it is white space number increases — MLSC, Feb 22 '14 at 06:05
@MortezaLSC There's no difference for string comparisons. Bourne shell supports `=` and Bash supports `==`. But they are synonymous in bash. — jaypal singh, Feb 22 '14 at 06:06
Ok I tried it ... but I want to check if it is null, number doesnt increase the value..and if it is white space, number increase its value — MLSC, Feb 22 '14 at 06:08

score 2 · Accepted Answer · answered Feb 22 '14 at 07:14

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 '14 at 07:14

jaypal singh

74,723
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102
147

1

Can you elaborate as to what didn't work? I tested it on my system. – jaypal singh Feb 22 '14 at 07:28
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. – Aleks-Daniel Jakimenko-A. Feb 22 '14 at 11:27

MelBurslan · Answer 2 · 2014-02-22T06:42:43.487

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 '14 at 06:42

answered Feb 22 '14 at 06:33

MelBurslan

2,383
4
18
26

I tested it, but the error has occured:unexpected EOF while looking for matching `}' ./j.sh: line 15: syntax error: unexpected end of file – MLSC Feb 22 '14 at 06:41
sorry.. I made a typographical error. Please see the first line, marked in the 2nd portion. – MelBurslan Feb 22 '14 at 06:43
It has no error but doesn't work properly..let me update my post by your solution..the see it – MLSC Feb 22 '14 at 06:49
when you run my version of the script and hit space then hit enter, what do you get? "1" or "wrong" – MelBurslan Feb 22 '14 at 06:54
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 – MelBurslan Feb 22 '14 at 07:15

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

2 Answers2