boolean question 2

[prosper]

This is a bash script

vmFound=false
if [ $vmFound ]; then
   echo "vmFound is true"
else
   echo "vmFound is false"
fi

Why "vmFound is true" is printed?
How could I modify the script to make it run with correct result?
I cannot find a tutorial with similar example
Thanks for any help

 

[Annihilannic]

The default check performed by [ somestring ] is whether a string is equivalent to [ -n somestring ], which returns true when the string is of non-zero length. Refer to the "CONDITIONAL EXPRESSIONS" secion of man bash.

So you could either do a string comparison, i.e.

if [ "$vmFound" == true ]; then

Or you could rely on the /usr/bin/true and /usr/bin/false binaries to return the correct value and simply use:

 if $vmFound; then

Annihilannic.

 

[Annihilannic]

Ignore "whether a string is" in my previous post... I meant to delete that.

Annihilannic.

 

[prosper]

Thanks for the answer and the detailed explanation

 

[feherke]

Hi

As an alternative, while you are using [tt]bash[/tt]. You can use C-like conditions, so 0 is false and any other integer is true :

[navy]vmFound[/navy][teal]=[/teal][purple]0[/purple]
[b]if[/b] [teal](([/teal] vmFound [teal]));[/teal] [b]then[/b]
  echo [green][i]"vmFound is true"[/i][/green]
[b]else[/b]
  echo [green][i]"vmFound is false"[/i][/green]
fi

The same works in [tt]ksh[/tt] too. ( Not sure if in all versions. )

Feherke.

http://rootshell.be/~feherke/