Check that a variable is a number in UNIX shell [duplicate] - unix

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How do I test if a variable is a number in Bash?
(40 answers)
Closed 1 year ago.
How do I check to see if a variable is a number, or contains a number, in UNIX shell?

Answer 1

if echo $var | egrep -q '^[0-9]+$'; then
# $var is a number
else
# $var is not a number
fi

Answer 2

Shell variables have no type, so the simplest way is to use the return type test command:
if [ $var -eq $var 2> /dev/null ]; then ...
(Or else parse it with a regexp)

Answer 3

No forks, no pipes. Pure POSIX shell:
case $var in
(*[!0-9]*|'') echo not a number;;
(*) echo a number;;
esac
(Assumes number := a string of digits). If you want to allow signed numbers with a single leading - or + as well, strip the optional sign like this:
case ${var#[-+]} in
(*[!0-9]*|'') echo not a number;;
(*) echo a number;;
esac

Answer 4

In either ksh93 or bash with the extglob option enabled:
if [[ $var == +([0-9]) ]]; then ...

Answer 5

Here's a version using only the features available in a bare-bones shell (ie it'd work in sh), and with one less process than using grep:
if expr "$var" : '[0-9][0-9]*$'>/dev/null; then
echo yes
else
echo no
fi
This checks that the $var represents only an integer; adjust the regexp to taste, and note that the expr regexp argument is implicitly anchored at the beginning.

Answer 6

This can be checked using regular expression.
###
echo $var|egrep '^[0-9]+$'
if [ $? -eq 0 ]; then
echo "$var is a number"
else
echo "$var is not a number"
fi

Answer 7

I'm kind of newbee on shell programming so I try to find out most easy and readable
It will just check the var is greater or same as 0
I think it's nice way to choose parameters... may be not what ever... :
if [ $var -ge 0 2>/dev/null ] ; then ...

Answer 8

INTEGER
if echo "$var" | egrep -q '^\-?[0-9]+$'; then
echo "$var is an integer"
else
echo "$var is not an integer"
fi
tests (with var=2 etc.):
2 is an integer
-2 is an integer
2.5 is not an integer
2b is not an integer
NUMBER
if echo "$var" | egrep -q '^\-?[0-9]*\.?[0-9]+$'; then
echo "$var is a number"
else
echo "$var is not a number"
fi
tests (with var=2 etc.):
2 is a number
-2 is a number
-2.6 is a number
-2.c6 is not a number
2. is not a number
2.0 is a number

Answer 9

if echo $var | egrep -q '^[0-9]+$'
Actually this does not work if var is multiline.
ie
var="123
qwer"
Especially if var comes from a file :
var=`cat var.txt`
This is the simplest :
if [ "$var" -eq "$var" ] 2> /dev/null
then echo yes
else echo no
fi

Answer 10

Here is the test without any regular expressions (tcsh code):
Create a file checknumber:
#! /usr/bin/env tcsh
if ( "$*" == "0" ) then
exit 0 # number
else
((echo "$*" | bc) > /tmp/tmp.txt) >& /dev/null
set tmp = `cat /tmp/tmp.txt`
rm -f /tmp/tmp/txt
if ( "$tmp" == "" || $tmp == 0 ) then
exit 1 # not a number
else
exit 0 # number
endif
endif
and run
chmod +x checknumber
Use
checknumber -3.45
and you'll got the result as errorlevel ($?).
You can optimise it easily.

Answer 11

( test ! -z "$num" && test "$num" -eq "$num" 2> /dev/null ) && {
# $num is a number
}

Answer 12

You can do that with simple test command.
$ test ab -eq 1 >/dev/null 2>&1
$ echo $?
2
$ test 21 -eq 1 >/dev/null 2>&1
$ echo $?
1
$ test 1 -eq 1 >/dev/null 2>&1
$ echo $?
0
So if the exit status is either 0 or 1 then it is a integer , but if the exis status is 2 then it is not a number.

Answer 13

a=123
if [ `echo $a | tr -d [:digit:] | wc -w` -eq 0 ]
then
echo numeric
else
echo ng
fi
numeric
a=12s3
if [ `echo $a | tr -d [:digit:] | wc -w` -eq 0 ]
then
echo numeric
else
echo ng
fi
ng

Answer 14

Taking the value from Command line and showing THE INPUT IS DECIMAL/NON-DECIMAL and NUMBER or not:
NUMBER=$1
IsDecimal=`echo "$NUMBER" | grep "\."`
if [ -n "$IsDecimal" ]
then
echo "$NUMBER is Decimal"
var1=`echo "$NUMBER" | cut -d"." -f1`
var2=`echo "$NUMBER" | cut -d"." -f2`
Digit1=`echo "$var1" | egrep '^-[0-9]+$'`
Digit2=`echo "$var1" | egrep '^[0-9]+$'`
Digit3=`echo "$var2" | egrep '^[0-9]+$'`
if [ -n "$Digit1" ] && [ -n "$Digit3" ]
then
echo "$NUMBER is a number"
elif [ -n "$Digit2" ] && [ -n "$Digit3" ]
then
echo "$NUMBER is a number"
else
echo "$NUMBER is not a number"
fi
else
echo "$NUMBER is not Decimal"
Digit1=`echo "$NUMBER" | egrep '^-[0-9]+$'`
Digit2=`echo "$NUMBER" | egrep '^[0-9]+$'`
if [ -n "$Digit1" ] || [ -n "$Digit2" ]; then
echo "$NUMBER is a number"
else
echo "$NUMBER is not a number"
fi
fi