If statement to determine whether a kernel is 32 or 64

Question

I'm trying to know whether a kernel is 64 or 32 in #!/bin/sh.

I build this code!

krnl=$(uname -i)

# Check whether 64 or 32 bit kernel and download the correct version;
if [ $krnl='i386' ] ; then # 32
  # Do 32-bits stuff
else
  # Do 64-bits stuff
fi

But it seems to return always true. What I'm doing wrong, Why this is happening and how I can fix this? What I googled always show me in bash or doesn't work.

Thanks in advance!

@ant There are some difference. But if you think so I can delete. — waldyr.ar, Aug 18 '12 at 22:01
it's not up to me alone to decide Sir, this is my opinion. Please do not delete based on my opinion — ant, Aug 18 '12 at 22:02
@ant even with that answer I could not make the if statement work. I could detect the kernel version, but I wont be able to distinguish. — waldyr.ar, Aug 18 '12 at 22:04
have you tried other options from the answer I marked as duplicate? i.e. `getconf LONG_BIT` should return `64` or `32`. Also have you used `==` instead of `=` in your if statement ? http://stackoverflow.com/a/7308155/169277 what does `uname -a` print ? — ant, Aug 18 '12 at 22:06
Not quite a duplicate because /bin/sh might not be bash, but the same answer does apply in practice. — Ganesh Sittampalam, Mar 06 '14 at 22:18

score 1 · Answer 1 · answered Aug 18 '12 at 21:39

1

Whitesapce is significant in bash. You need spaces around the '=' character, like so:

if [ $krnl = 'i386' ] ; then # 32

Otherwise, you've defined a long string "x86_64=i386" or "i386=i386", and the non-empty string returns true.

answered Aug 18 '12 at 21:39

Pat

1,882
2
15
22

score 1 · Accepted Answer · answered Aug 18 '12 at 21:43

1

Spaces are needed around '=' sign to properly test $krnl value:

krnl=$(uname -i)

# Check whether 64 or 32 bit kernel and download the correct version;
if [ $krnl = 'i386' ] ; then # 32
  # Do 32-bits stuff
else
  # Do 64-bits stuff
fi

answered Aug 18 '12 at 21:43

Stephane Rouberol

4,286
19
18

score 0 · Answer 3 · answered Aug 18 '12 at 21:37

You have to put spaces around the equals sign in the [ command. Otherwise, it gets a single argument and returns true if that argument is not an empty string, which it will never be.

Also, uname -m might be better. I get "unknown" from uname -i on an amd64 machine.

score 0 · Answer 4 · answered Aug 18 '12 at 21:39

0

On my machine, uname -p returns i686 whereas uname -i returns i386.

answered Aug 18 '12 at 21:39

AGS

14,288
5
52
67

ant · Answer 5 · 2012-08-18T21:54:39.550

0

In my console uname -m, uname -i and uname -p return x86_64 so :

krnl=`uname -i`

if [ $krnl="x86_64" ] ; then # 64
  echo "64"
else
  echo "32"
fi

~~should work~~ works on my machine.

Update :

krnl=`uname -i`
if [ "$krnl" == "x86_64" ]; then
        echo "64"
else
        echo "32"
fi

When I change to :

if [ "$krnl" != "x86_64" ]; then

echoes 32

edited Aug 18 '12 at 21:54

answered Aug 18 '12 at 21:40

ant

22,634
36
132
182

You haven't fixed the spacing problem, all you did is reverse it so it always takes the 64 branch instead of always taking the 32 branch. It's still wrong. – Alan Curry Aug 18 '12 at 21:45
you were right but for different reasons (I didn't just swap). take a look at the edited question – ant Aug 18 '12 at 21:55
this is the correct answer I see no reason for down-vote http://stackoverflow.com/a/106416/169277 – ant Aug 18 '12 at 21:59
The updated version is not as bad. The first one is just wrong. Using `==` in a `[` command is a bashism though. – Alan Curry Aug 18 '12 at 22:12
true story, `= ''` works as well – ant Aug 18 '12 at 22:13

If statement to determine whether a kernel is 32 or 64

5 Answers5