Shell脚本中的OR条件-Unix

Question

I declare three variables.

$1=`ssh <server_1> cat /etc/passswd|cut -f -d:|grep -e $IID -e $EID`
$2=`ssh <server_2> cat /etc/shadow|cut -f -d:|grep -e $IID -e $EID`
$3=`ssh <server_3> cat /etc/passwd}|cut -f -d:|grep -i $CID`

The above three variables are created by taking ssh to servers and checking the presence of the IDs which I give as input. If the ID doesn't exist already, the the variable is going to be null.

Now, how do I verify if all the three variables are null. I wanted to use the OR condition specified within an IF.

I tried,

if [ -s "$1" -o  -s "$2" -o  -s "$3"];then
echo -$1 $2 $3 "already exist(s)"

It didnt work. Please advise.

PS: I have just begun my career in Unix and correct me If am wrong anywhere.

Answer 1

Several points.

When you assign to a variable, don't use the dollar sign:

foo=xxx

Variables $1 , $2 etc are already used for your command line arguments. Pick other names. But not $4 please. :-)

When you specify a command for ssh, and it has arguments, it has to be quoted, because the command needs to be a single argument for ssh. In your case use double quotes, as you want variable expansion for $IID etc.

Most Unix utils are able to open input files themselves, so you don't need to start your pipeline with cat .

foo=`ssh <server_1> "cut -f -d: /etc/passwd | grep -e $IID -e $EID"`

Or something like that.

Answer 2

It was a typo in my question. I had actually declared it as,

1=`ssh <server_1> cat /etc/passswd|cut -f -d:|grep -e $IID -e $EID` 
2=`ssh <server_2> cat /etc/shadow|cut -f -d:|grep -e $IID -e $EID` and so on. 

And I tried it as ,

if [ -s "$1" -o  -s "$2" -o  -s "$3"];then
echo -e $1 $2 $3 "already exist(s)"

Since I had to Deliver my script today, I used the conventional method of,

ssh <server_1> "cat /etc/passswd|cut -f -d:|grep -e $IID -e $EID" > file1
ssh <server_2> "cat /etc/shadow|cut -f -d:|grep -e $IID -e $EID" > file2
ssh <server_3> "cat /etc/passwd|cut -f -d:|grep -ix $CID" > file3

if [ -s file1 -o -s file2 -o -s file3]; then
for i in `cat file1 file2 file3`
do
echo $i "already exists"
done
else

And I have now learnt from my first post, that -s to ensure that a file is not empty and -z is to ensure string is empty.