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Danrol
n00b
Joined: 23 Feb 2003
Posts: 23
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 Posted: Sat May 31, 2003 1:11 pm Post subject: expr And Decimals |
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I'm trying to learn more about BASH scripting, so I've decided to write a script to calculate the cost of fuel for a car journey.
The problem I have is that expr doesn't seem to like decimal numbers. For example, echo `expr 2.5 + 1` returns with 'expr: non-numeric argument'.
After Googling it seems it it should work the way I am trying.
I also tried different combinations of quotes without success....
Can anyone give me suggestion? Am I missing something obvious? |
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grant.mcdorman
Apprentice
Joined: 29 Jan 2003
Posts: 295
Location: Toronto, ON, Canada
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| Posted: Sat May 31, 2003 3:49 pm Post subject: Re: expr And Decimals |
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| Danrol wrote: | I'm trying to learn more about BASH scripting, so I've decided to write a script to calculate the cost of fuel for a car journey.
The problem I have is that expr doesn't seem to like decimal numbers. For example, echo `expr 2.5 + 1` returns with 'expr: non-numeric argument'.
After Googling it seems it it should work the way I am trying.
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The quoted reference page isn't for the expr program, but for a Perl operator (i.e. it won't work for shell scripting).
The expr program doesn't support decimals - only integers. If you want to decimal arithmetic, try something like this:
| Code: | value=`echo 2.5+1 | bc`
echo $value
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By the way, if you are using bash (or the Korn shell, ksh) then integer arithmetic can be done more effectively by instead of . In addition, the newer way of doing the shell substitution (back quotes) is $(): However, neither of these ways will work with the Bourne shell, which is the standard scripting language on most Unix systems. |
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Danrol
n00b
Joined: 23 Feb 2003
Posts: 23
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| Posted: Sat May 31, 2003 8:24 pm Post subject: |
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| Many thanks for your help, it's all starting to make sense now. |
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zhenlin
Veteran
Joined: 09 Nov 2002
Posts: 1361
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| Posted: Sun Jun 01, 2003 12:45 am Post subject: |
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| I thought integer arithmetic was done using $((1+1))... |
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grant.mcdorman
Apprentice
Joined: 29 Jan 2003
Posts: 295
Location: Toronto, ON, Canada
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| Posted: Sun Jun 01, 2003 1:08 am Post subject: |
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| zhenlin wrote: | | I thought integer arithmetic was done using $((1+1))... |
It's the same thing. bash tends to incorporate scripting features from many shells, so it may be that one Korn shell variant used $(()), and another $[]. You're correct that the bash man and info pages only mention $(()), though - I'm not sure why. |
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