Test if a directory is writable by a given UID?

Question

We can test if a directory is writable by the uid of the current process:

if [ -w $directory ] ; then echo \'Eureka!\' ; fi

But can anyone

Answer 1

One funny possibility (but it's not bash anymore) is to make a C program with the suid flag, owned by mysql.

Step 1.

Create this wonderful C source file, and call it caniwrite.c (sorry, I've always sucked at choosing names):

#define _GNU_SOURCE
#include 
#include 
#include 

int main(int argc,char* argv[]) {
   int i;
   for(i=1;i

Step 2.

Compile:

gcc -Wall -ocaniwrite caniwrite.c

Step 3.

Move it in whatever folder you like, /usr/local/bin/ being a good choice, change it's ownership and set the suid flag: (do this as root)

# mv -nv caniwrite /usr/local/bin
# chown mysql:mysql /usr/local/bin/caniwrite
# chmod +s /usr/local/bin/caniwrite

Done!

Just call it as:

if caniwrite folder1; then
    echo "folder1 is writable"
else
    echo "folder1 is not writable"
fi

In fact, you can call caniwrite with as many arguments as you wish. If all the directories (or files) are writable, then the return code is true, otherwise the return code is false.