How to check file owner in linux

Question

How to check file owner in linux

i am trying to run this bash file

#!/bin/bash
uname2=$(ls -l $1 | awk '{print $3}');
if [ $uname2 == $USER ]
then echo owner
else echo no owner
fi

it gives error ==' unary operator expected. what is wrong? ubuntu server 10.04.

Answer 1

Use = not == for comparison. The test(1) man page says:

STRING1 = STRING2
       the strings are equal

I'd also recommend using stat to find out the owner instead of some ls hacks. Some double quotes and an extra x would also be nice.

#!/bin/bash
uname2="$(stat --format '%U' "$1")"
if [ "x${uname2}" = "x${USER}" ]; then
    echo owner
else
    echo no owner
fi

Answer 2

Try running your script with bash -x and you can see exactly what's going on. I bet that one of your variables is empty. You can protect against this by quoting the variables, like this:

if [ "$uname2" == "$USER" ]

Answer 3

You forgot to put " next to variables.

uname2=$(ls -l $1 | awk '{print $3}');
if [ "$uname2" == "$USER" ]
then echo owner
else echo no owner
fi

Answer 4

You want:

#!/bin/bash
uname2=$(ls -ld $1 | awk '{print $3}' | tail -1);
if [ "$uname2" == "$USER" ]
then echo owner
else echo no owner
fi

Your output contains multiple lines, and the first line is going to be blank. So snag the last one with tail . Also, as others have pointed out, the best practice is to use quotes in your arguments. That way you won't end up with an incomplete command in the case of a blank variable, etc.

You also want to include d in the argument list to ls so that this works properly with directories. (checks if the directory has an owner) Otherwise you'll just get the last file in the directory.

Answer 5

There is one simple option available to check whether file is owned by the use or not, who is executing current script.

if [[ -O "$0" ]]; then
    echo "owner"
else
    echo "no owner"
fi