comparison expression, help pls... 1

[h3nd]

Hi guys,

I try to compare my variable which called $number.
And $number could be integer or decimal.

when I tried using comparison like this :

if [[ $number -lt 5 ]]

it works only for if $number is integer, if $number is not decimal (such as 4.5). It didnt work.

But when I tried using comparison like this :

if [[ $number<5 ]]

It worked for decimal but,
The problem is if $number is 13, $number is gonna less than 5. Because it just compare the first digit.

So, what comparison should I use to compare the number which is decimal or integer.

Thanks guys.

 

[columb]

Hmm
What OS and shell are you using. On AIX 4.3 using ksh I get

europa:/home/root:(ROOT)> [[ 4.5 -lt 5 ]] && echo yes
yes
europa:/home/root:(ROOT)> number="4.5"
europa:/home/root:(ROOT)> [[ $number -lt 5 ]] && echo yes
yes
europa:/home/root:(ROOT)> number="5.5"
europa:/home/root:(ROOT)> [[ $number -lt 5 ]] && echo yes
europa:/home/root:(ROOT)>

which, as you can see, is working fine. What 'didn't work'?

Ceci n'est pas une signature
Columb Healy

 

[h3nd]

Thx columb,

I'm using Linux RedHat, here's what I've got

[t003947@ypprod01 Script]$ number="3.5"
[t003947@ypprod01 Script]$ [[ $number -lt 5 ]] && echo yes
-bash: [[: 3.5: syntax error in expression (error token is ".5")

 

[h3nd]

And I've tried in ksh as well

[t003947@ypprod01 Script]$ ksh
$ number="3.5"
$ [[ $number -lt 5 ]] && echo yes
ksh: 3.5: unexpected `.'

 

[columb]

Try

expr $number \< 5 >/dev/null && echo yes

I once heard expr described as the 'Swiss Army Knife' command!

Ceci n'est pas une signature
Columb Healy

 

[h3nd]

Thanks columb,

It works!

 

[Mike042]

Hi h3nd,

The root of this 'comparison problem' is that there are 'strings' and 'numbers'. Unix provides 'operators' for comparing strings, eg: = (equal) and != (not equal) and for comparing numbers, eg: -eq (equal) and -ne (not equal)
If you compare '5' with '10' as strings then '5' is greater than '10' because ASCII 5 (53) is greater than ASCII 1 (49). If you compare them as numbers then '5' is less than '10'.
[[ $number -lt 10 ]] # compares strings using 'number comparitor'
[[ number -lt 10 ]] # compares numbers using 'number comparitor'
[[ $number < 10 ]] # compares strings using 'string comparitor'
[[ number < 10 ]] # compares numbers using 'string comparitor'
Try setting number to 5 and check the above 4 comparisons.

I hope that helps.

Mike

 

[h3nd]

Hi Mike042,

I've tried all your possibility up there, and I put number="3.5"

Here's the result :

$ number="3.5"
$ [[ "number" -lt "5" ]] && echo yes
ksh: 3.5: unexpected `.'
$ [[ "$number" -lt "5" ]] && echo yes
ksh: 3.5: unexpected `.'
$ [[ "number"<"5" ]] && echo yes
$ [[ "$number"<"5" ]] && echo yes
yes

the only thing worked only the last one, but as I mentioned above. The last one couldn't be worked for certain number such as (10,20,30,...)

 

[Mike042]

Hi h3nd,

Please note that none of my examples had quotes. You can can use quotes around strings, but not around numbers.

I hope that helps.

Mike

 

[SamBones]

For numerical comparisons in Korn shell, use the double parenthesis "(( ))", not the double brackets "[[ ]]".

$ NN=3.5
$ (( $NN < 5 )) && print Yes
Yes
$ NN=5.5
$ (( $NN < 5 )) && print Yes
$ NN=33.5
$ (( $NN < 5 )) && print Yes
$

The only problem is that it's not actually comparing the decimals, only the integer part of the number.

$ NN=5.5
$ (( $NN < 5.6 )) && print Yes
$ (( $NN < 5.3 )) && print Yes                                                                          
$

 

[h3nd]

I think the best still using the code from 'Swiss Army Knife' command. Which posted by columb.

It works in every condition.