LinuxQuestions.org - [SOLVED] if statement options in bash script

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if statement options in bash script

I have a bash script (not mine) that is generating some errors. I'm trying to fix that but there is a section that I do not understand.

Code:

snpsOALib=`OA_MODE=opt $OA_ROOT/bin/oaGetLibPath`

if [ $? != 0 ] || [ ! -d $snpsOALib ]; then

    echo "Error: Incomplete installation. OpenAccess is missing or improperly installed."

    exit 1

fi

export OA_ROOT

$OA_ROOT is a directory
I don't know what $? is .. I thought it's a variable but that is the only one written in the file(it is not defined before,neither $? nor ?).

now what does this If statement mean ?? can somebody explain ??

$? is the exit code of the last command
when exit code is 0 it means no error, and none-zero code is an Error

try it with a few things

true;echo $?
false;echo $?
ffaallssee;echo $?

so what is happening which with the script is

Code:

snpsOALib=`OA_MODE=opt $OA_ROOT/bin/oaGetLibPath`

# set snpsOALib as output of command "OA_MODE=opt $OA_ROOT/bin/oaGetLibPath"

if [ $? != 0 ] || [ ! -d $snpsOALib ]; then

# if last command gave error ( not equal to 0 ) OR $snpsOALib is not a directory

    echo "Error: Incomplete installation. OpenAccess is missing or improperly installed."

# above prints error msg, below exits the script ( with exit code 1 )

    exit 1

fi

export OA_ROOT

Open Audit?

err. n/m

Incidentally, '!=' is the wrong operator for a numeric comparison; it should be '-ne', or use (( )) instead of [[ ]] http://tldp.org/LDP/abs/html/comparison-ops.html: