howto check string is integer?

ygloo · 10-14-2006, 08:55 AM

bash:
howto check string is integer?

MensaWater · 10-14-2006, 10:59 AM

Use expr command to multiply it by 1. If its not a number it will tell you so. If it is a number it will just give you the original number.

Script to do same follows. Just vi a file called "testint.sh" and insert this code. Run it from command line as:

testint.sh INPUT

Where INPUT is the item you are testing. (Make sure to add execute bit with chmod command or run it as "sh testint.sh INPUT" instead.)

Code:

#!/bin/bash
#
# First multiply the input argument times 1.  If input is a number this will
# result in original number.  Otherwise it will error out.  Send output and
# error to /dev/null so they don't show up on screen.
#
# Put that inside a conditional.  If return fom the expr command is false it
# is not an integer.  If it is true then it is an integer.

if expr $1 \* 1 >/dev/null 2>&1
then echo it is an integer
else echo it is not an integer
fi

demon_vox · 10-14-2006, 11:05 AM

There might be better ways, but this one is the one I can think of right now:

Code:

echo $MY_VAR  | grep "^[[:digit:]][[:digit:]]*$" > /dev/null
# NO CODE HERE OR YOU CAN OVERWRITE $? !!!!
if [ "$?" -eq 0 ]; then
	echo "Its a number"
else
	echo "its a string"
fi

Hope this is useful.
Cheers!

Disillusionist · 10-14-2006, 11:08 AM

Code:

###
### Sample script
###

# Set variable l_string to a valid integer
l_string="10" 

# use sed to remove a leading + or - symbol and replace
# one or more numbers from 0-9 from the string and count
# the remaining characters ( should leave one character )

l_is_int=`echo $l_string|sed 's/^[+-]//g'| \
sed 's/[0-9][0-9]*//g'|wc -c`

if [ $l_is_int == 1 ]
then
   echo "l_string is a valid integer value"
else
   echo "l_string is not a valid integer value"
fi

ygloo · 10-14-2006, 11:09 AM

Code:

read 

expr $REPLY + 0 > /dev/null || exit 1
# this works

Code:

case "$REPLY" in
*[0-9]*  ) true   # woks when string is - 22424 or sdfasdjfasdj, when mixed - dsf435 or 345dsf - not workin
esac