A simple way to detect an odd or even number in bash

[technosaurus]

for a non bashism version (as long as parameters don't contain spaces)

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isnumber() [[ $(($1+0)) = ${1} ]]

AFAIK double brackets are not POSIX compliant though bash supports them also in its "more closely to the POSIX standard" mode.

crap, you are right, always get that backwards - it should still work if you change them to single brackets as long as the parameters are quoted or don't contain spaces, newlines or tabs. FWIW both busybox shells (ash and hush) support both forms.

[MochiMoppel]

it should still work if you change them to single brackets as long as the parameters are quoted or don't contain spaces, newlines or tabs

No, it does not work
- A single bracket is an ordinary command. The function requires curly braces.
- $(($1+0)) will generate an irrecoverable syntax error if the parameter contains a decimal separator, which makes this test unsuitable as an integer check. Same happens with double brackets.

The following code should work better. Spaces etc. in parameters will lead to a correct "not an integer" result
Decimal separators will not generate a fatal syntax error.

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isnumber() { test "$@" -eq "$@"  2>/dev/null ;}

[technosaurus]

The function requires curly braces.

It can be any compound statement which also includes a subshell "( ... )" in Posix and "[[ ... ]]" in bash, ksh (since 1988) and any modern shell including busybox and just about everything but dash. I didn't realize that even with "{ ... }", the compound statement can also be followed by redirection of stdin, stdout, stderr (useful for logging). The double bracket version does have some subtle differences though. I seem to have gotten a bit rusty on my shell programming. Likely because I have been using C primarily for the last few years and mostly awk right before that. Perhaps I should write myself a manual as I relearn it for the next time I forget. Tentatively titled "The Portable Shell Scripting Guide" as an answer to "The Advanced Bash Scripting Guide" ... DashAsBinSh mainly describes pitfalls without offering solutions

[NeroVance]

When i was learning Pascal in high school i was using this formula before i noticed that Pascal has odd function built-in.

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#!/bin/sh
check=`expr $1 / 2 \* 2`
if [ $check != $1 ]
then
  echo "$1 is odd"
else
  echo "$1 is even"
fi

You learned Pascal in high school? You must be very old?!?!

Oddly enough I'm only 24, but my older sister learned Pascal in High School from what I recall.

[musher0]

That's funny. Being 24 is not odd! Being 24 is being young!

I was saying that because Pascal is an old computer language,
as computer languages go.

[jafadmin]

Check the least significant bit: ((($MyVal&1)==0))

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  MyVal=221;((($MyVal&1)==0)) && echo "$MyVal is even" || echo "$MyVal is odd"

Or ...

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if (($MyVal&1))
then 	echo "$MyVal is odd"
else 	echo "$MyVal is even"
fi

In C:

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int MyVal = 332;
printf( "Value of MyVal is %s\n", (MyVal&1) ? "odd": "even" );