How to check whether a string is number or not

Shell Programming and Scripting
1

Hi ,
I am facing a problem .. which looks simple... but took 2 days of mine.. even now it is not solved completely..

I have one variable..., want to know whether that variable contains number... canbe +ve or -ve ...

Values
+35 --- number
-43 --- number
45A -- non number
34+45 -- non number

please help me
Shihab

2

Look at the solution given in this post

Let me knows if it falters for any condition.

Vino

3

Another solution vaild only for integers, decimals not allowed :smiley:

#!/bin/ksh
echo "Enter val : \c"
read num
expr $num + 1 2> /dev/null
if [ $? = 0 ]
then
echo "Val was numeric"
else
echo "Val was non-numeric"
fi

rishi :o

4

Hi rishi ,
It won't work if the number is like +567
example expr +567 + 1 .. will fail

Regards
Shihab

5

if u r using tcl or perl there is finction calles isnumber

if [ isnumber $a ] {
}
:cool:

6

A small edit Shihab,

#!/bin/ksh
echo "Enter val : \c"
read num
expr "$num + 1" 2> /dev/null
if [ $? = 0 ]
then
echo "Val was numeric"
else
echo "Val was non-numeric"
fi

Note the double qutoes around the expression.

Rishi

7

how abt this,

[[ `echo $num | sed 's/^[-+0-9][0-9]*//' | wc -c` -eq 1 ]] && echo "itz number" && exit 0
echo "itz not number"

not thoroughly tested
plz let me know, if it faints somewhere

8

The problem can easily be solved by considering what a "number" is actually and since this is a good opportunity to show how to develop regular expressions I will explain that in greater detail:

1st Try
The only characters allowed should be 0-9. This covers for "123", but not for "123.0". Hence

2nd Try
Only 0-9 are allowed, save for exactly 1 character, which may be a fullstop. This definition covers "123" and "456.78", leaves out (quite correctly) "123.456.789", but doesn't cover "-123.0" or "+123.0". Hence

3rd Try
In addition to 2nd Try the first character may be "+" or "-" optionally. This covers every number and leaves out any non-number, so this solution is perfect.

We develop a simple sed-statement from there, by consecutively throwing out all "allowed" chars and look, if something remains. If something remains it is non-numeric, if not, then it is numeric:

if [ -n "$( print - "$VarInQuestion"           |\
            sed 's/^[+-]//;s/[0-9]//g;s/\.//'   \
          )" ] ; then
     print - "$VarInQuestion is non-numeric"
else
     print - "$VarInQuestion is numeric"
fi

Here is the sed-statement in detail:

s/^[+-]// - see 3rd try, we chop off leading +/- signs
s/[0-9]//g - see 1st try, we throw out all numerical digits
s/\.// - see 2nd try, we throw out one possible decimal point

bakunin

9

Hi All..
Thanks a lot....
It is working fine now...
Shihab

10 
$
$ x=1; if [ "`expr $x - $x 2>/dev/null`" == "0" ]; then echo is number; else echo not number; fi
is number
$ x=-1; if [ "`expr $x - $x 2>/dev/null`" == "0" ]; then echo is number; else echo not number; fi
is number
$ x=a; if [ "`expr $x - $x 2>/dev/null`" == "0" ]; then echo is number; else echo not number; fi
not number
$ x=1a; if [ "`expr $x - $x 2>/dev/null`" == "0" ]; then echo is number; else echo not number; fi
not number
$
11

This solution is better as it works for decimals as well:

$ x=a; printf "%g" $x >/dev/null 2>&1; if [ $? -eq 0 ]; then echo is number; else echo not number; fi
not number
$ x=9a; printf "%g" $x >/dev/null 2>&1; if [ $? -eq 0 ]; then echo is number; else echo not number; fi
not number
$ x=9; printf "%g" $x >/dev/null 2>&1; if [ $? -eq 0 ]; then echo is number; else echo not number; fi
is number
$ x=9.1; printf "%g" $x >/dev/null 2>&1; if [ $? -eq 0 ]; then echo is number; else echo not number; fi
is number
$ x=-9.1; printf "%g" $x >/dev/null 2>&1; if [ $? -eq 0 ]; then echo is number; else echo not number; fi
is number
$ x=-9; printf "%g" $x >/dev/null 2>&1; if [ $? -eq 0 ]; then echo is number; else echo not number; fi
is number
12 
awk '$1+0==$1' a.txt
13

try this:

function validatenumber
{
number="$1"
if [ -z $number ];then
echo "not  something" > &2;return 1
fi

if [ "${number%${number#?}} = "-" ]; then
testvalue="${number#?}"
fi

if [ "${number%${number#?}} = "+" ]; then
testvalue="${number#?}"
fi

nodigits="$(echo $testvalue | sed 's/[[:digit:]]]//g')"
if [ ! -z $nodigits ]; then
echo "Invalid Number" > &2
return 1
fi

return 0
}

if validatenumber "$1"; then
echo "No is a valid integer"
fi

cheers,
Devaraj Takhellambam