Test for integer in BASH

minil · 01-18-2005, 06:03 AM

Hi
How to test entered data is integer or not in Bash Shell program.

Thanks in advance

homey · 01-18-2005, 06:27 AM

Something like this may get you started...

Code:

#!/bin/bash

a=100
if [[ $a != [0-9]* ]]; then
echo not an integer
else
echo $a
fi

minil · 01-18-2005, 06:59 AM

if line 3 has single [ ]
----------------------------

1 #!/bin/bash
2 a=100
3 if [ $a != [0-9]* ]; then
4 echo "not an integer"
5 else
6 echo $a
7 fi

output

not an integer

------------------------------------
if line 3 has double [[ ]]

----------------------------

1 #!/bin/bash
2 a=100
3 if [ $a != [0-9]* ]; then
4 echo "not an integer"
5 else
6 echo $a
7 fi

output

100

----------------------------------
why ??

minil · 01-18-2005, 07:00 AM

sorry

line 3 of second code should be

if [[ $a != [0-9]* ]]; then

homey · 01-18-2005, 07:57 AM

This site has a lot of scripting goodies.

http://www.tldp.org/LDP/abs/html/

minil · 01-19-2005, 01:03 AM

thanks a lot homey

bigearsbilly · 01-19-2005, 08:55 AM

look at typeset -i too.
bash and ksh

trevelluk · 02-25-2005, 09:27 AM

Hi everyone.

It looks to me like homey's script doesn't quite work right. For example:

Code:

#!/bin/bash

a=100a
if [[ $a != [0-9]* ]]; then
echo not an integer
else
echo $a
fi

will output 100a.

This script got me thinking though, and I the following seems to work.

Code:

#!/bin/bash

a=100
if [ "`echo $a | egrep ^[[:digit:]]+$`" = "" ]; then
    echo not an integer
else
    echo $a
fi

This outputs 100. If a is set to '100a', then it will output 'not an integer.'

Hope this helps!

LasseW · 02-25-2005, 12:51 PM

Let test do the job:

a=100a
test $a -eq 0 2>/dev/null
if [ $? -eq 2 ]; then
echo not an integer
else
echo $a
fi

Brain Drop · 02-25-2005, 11:49 PM

I came up with this way (who else has one?), this way also declares it as an integer at the same time for better efficiency.

Code:

#!/bin/bash
declare -i a=100 2>/dev/null
if [ $? -ne 0 ]
        then
         echo no
        else
          echo $a
fi

dustu76 · 02-27-2005, 06:09 AM

Its better to use typeset than declare. They essentially do the same thing & typeset works with ksh too (declare doesnt).

HTH.

Brain Drop · 02-27-2005, 05:04 PM

Yes, however, typeset doesn't work with tcsh, and declare does. It shouldn't matter in this case anyway, since it starts with !#/bin/bash.

niall · 03-07-2005, 05:05 AM

You can also use expr to ensure a variable is numeric

a=100

if [ `expr $a + 1 2> /dev/null` ] ; then
echo $a is numeric ;
else
echo $a is not numeric ;
fi ;

tostay2003 · 11-26-2008, 10:24 AM

Quote:

Originally Posted by niall

You can also use expr to ensure a variable is numeric

a=100

if [ `expr $a + 1 2> /dev/null` ] ; then
echo $a is numeric ;
else
echo $a is not numeric ;
fi ;

Isn't there a direct command to check this?

chrism01 · 11-26-2008, 06:04 PM

No. Shell is a very basic lang, and all internal arithmetic is integer only. You have to use external cmds like bc to do floating point.
You might also look at bash regexes, if you've got v3 http://www.tldp.org/LDP/abs/html/bas...#REGEXMATCHREF