Kindly tell me that is it necessary to use "expr" keyword.
EG:-
echo `expr a*b`
And where we can simply handle arithmetic expressions using simple arithmetic operators.
EG:-
echo a*b
Thanks in advance.
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I am using bash shell.Is first method mentioned in question cannot be used for evaluating arithmetic expressions?Adnan– Adnan2011-07-05 18:12:25 +00:00Commented Jul 5, 2011 at 18:12
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3 Answers
In a Posix shell you can evaluate expressions directly in the shell when they are enclosed in
$(( ... ))
So:
a=12
b=34
echo $(($a + $b))
And although this wasn't always the case, all Posix shells you are likely to encounter will also deal with:
echo $((a + b))
This all happened because, a long time ago, the shell did not do arithmetic, and so the external program expr was written. These days, expr is usually a builtin (in addition to still being in /bin) and there is the Posix $((...)) syntax available. If $((...)) had been around from day one there would be no expr.
The shell is not exactly a normal computer language, and not exactly a macro processor: it's a CLI. It doesn't do inline expressions; an unquoted * is a wildcard for filename matching, because a CLI needs to reference files more often than it needs to do arithmetic.
Comments
The second form will almost surely never do what you want. In Bash, you have a built-in numeric expression handler, though:
A=4; B=6; echo $((A * B))
Comments
You can do arithmatic using $(())
echo $((2*3))
results in 6
