ksh script needing an interger cmd. line arg

[Marc Ahrendt]

what is the best way to test that the 3rd command line argument for my ksh script is a positive interger?

./my_script A B C
C needs to be >=0 and an integer

[Paula J Frazer-Campbell]

Hi

if (( $c >= 0 ))
then

fi

Paula

[linuxfan]

Hi Marc,


you could do something simple like

if [ $3 -gt 0 ]
then
echo "3rd argument greater then 0"
fi

-Ramesh

[linuxfan]

Hi Marc,

for >=0 change it to

if [ $3 -ge 0 ]
then
echo "3rd argument greater then 0"
fi

-Ramesh

[Sridhar Bhaskarla]

First I will see if it is an integer or not

echo "$3 + 1 " |bc 2>&1 |grep syntax > /dev/null
if [ $? = 0 ]
then
echo "Your C is some character"
exit
fi

#Once the above is passed, it means it's an integer. Now I will check to see if it is > 0.

if [ $3 -gt 0 ]
then
echo "C should be greater than 0"
exit 1
fi

...code...

-Sri

[Sridhar Bhaskarla]

ooooopsss.. Small correction.. Friday evening.

yaada..yadaa..yadaaa..
...
if [ $3 -le 0 ]
then
echo "Arg 3 should be greater than 0"
exit
fi

...code...

[James R. Ferguson · Accepted solution]

Hi Marc:

Here's one somewhat rigorous way:

#!/usr/bin/sh
#
typeset X=$3
#
[ -z "$X" ] && { echo "no argument provided";exit 2; }
#
[ `expr $X : '[0-9]*'` -ne `expr $X : '.*'` ] && { echo "not a positive integer"
;exit 1; }
#
[ "$X" -le 0 ] && { echo "zero not allowed";exit 1; }
#
echo "OK"
exit 0
#
#.end.

...JRF...

[Paula J Frazer-Campbell]

Hi to all

As I am still learning scripting why use "gt" instead of >= ?

Paula

[Sridhar Bhaskarla]

Doesn't matter with POSIX. I personally commit syntax errors if I try the symbols like instead >= I type in => etc., it's more easy to remember gt, ge etc.

-Sri

[Marc Ahrendt]

thx for everyone's quick replies

sridhar, your solution does not work reliably for all possible input

james, yours works and is more compact than my crude attempt with grep and regular expressions, but i was hoping there was something built into the shell/test like "if (( -I $3 ))" where I would be that magical test on a number

[Sridhar Bhaskarla]

Marc,

Interesting. Did you have any instance where it couldn't get to work?. That will help me rectify my logic.

-Sri

[Marc Ahrendt]

sridhar, below succeeds and f is not an interger
echo "f + 5" | bc 2>&1

[Sridhar Bhaskarla]

Didn't have a system infront of me now. But I know where it would be missing. Try this out.

....
echo "${3}.1 + 1 " |bc 2>&1 |grep syntax > /dev/null
............

if [ $? = 0 ]

....

Thanks for letting me know.

-Sri