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Re: bash is not capable of comparing of strings and real numbers


From: DennisW
Subject: Re: bash is not capable of comparing of strings and real numbers
Date: Mon, 7 Dec 2009 17:08:02 -0800 (PST)
User-agent: G2/1.0

On Dec 7, 4:22 pm, pk <address@hidden> wrote:
> phani krishna jampala wrote:
> > bash is not capable of comparing of strings ( imean interms of lessthan or
> > greater than etc)
>
> It is, if you use [[  ]]
>
> a="abcd"
> b="bcde"
> if [[ "$b" > "$a" ]]; then
>   echo "$b is greater than $a"
> fi
>
> > and real numbers ( the float values).
>
> True, but I can't really speak as to whether this is planned or not (I think
> it isn't, but of course I might be wrong).

Since printf understands floats (or acts like it does), you can use it
plus a little care and luck to do float comparisons in Bash:

$ a=.3
$ b=0.2
$ [[ $a < $b ]] && echo true || echo false
true     # WRONG
$ printf -v a "%0.2f" $a
$ printf -v b "%0.2f" $b
$ [[ $a < $b ]] && echo true || echo false
false    # CORRECT
echo "$a $b"
0.30 0.20

$ a=147.1
$ b=23
$ [[ $a < $b ]] && echo true || echo false
true     # WRONG
$ printf -v a "%08.2f" $a
$ printf -v b "%08.2f" $b
$ [[ $a < $b ]] && echo true || echo false
false    # CORRECT
echo "$a $b"
00147.10 00023.00


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