Mailinglist Archive: opensuse (2532 mails)

[Anders Johansson <ajh@xxxxxxxxxx>]

On Sunday 04 May 2008 22:12:54 David C. Rankin wrote:
> Listmates,
>
>       I ran across this bash test for integers and it works brilliantly. It 
> was
> quite a contrast to the myriad of case $x in ... *[0-9+-]* ... approaches I
> ran across. I don't know exactly how it works, but only that it works --
> apparently great.
>
>       If anyone could shed some light on how it works it would be 
> appreciated. I
> presume it works based upon the differences in the way string and numerical
> data is held in memory or in a difference in what [ $AM_I_INT ] actually
> returns and the way the test is carried out. But that is no more than a
> guess. If anyone has a need, this is a great solution:
>
> AM_I_INT="$1"
>
> if [ $AM_I_INT -eq $AM_I_INT 2> /dev/null ]; then
> echo -e "\n\t$AM_I_INT is an integer\n"
> else
> echo -e "\n\t$AM_I_INT is not an integer\n"
> fi

If you read the man page for "test" you see that -eq expects integers. If you 
remove the 2>/dev/null you see that if it's not an integer, it throws an 
error message. So it "breaks" if it's not an integer, but at the same time it 
returns "false", so the if-statement as a whole works

Anders
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