How to tell the difference between “No such file or directory” and “Permission Denied”

file-permissionsunix

I'd rather not parse STDERR, but I can't think of another way to tell the difference, programmatically, between the two:

$ ls /net/foo.example.com/bar/test
/net/foo.example.com/bar/test: Permission denied
$ ls /sdfsdf
/sdfsdf: No such file or directory

No matter what command I try, they both seem to return the same error code, so that's a dead-end:

$ ls /net/foo.example.com/bar/test
/net/foo.example.com/bar/test: Permission denied
$ echo $?
2
$ ls /sdfsdf
/sdfsdf: No such file or directory
$ echo $?
2

I've tried the various file tests in perl, but they both return the same codes as well.

Best Answer

Test the file instead.

test -e /etc/shadow && echo The file is there

test -f /etc/shadow && echo The file is a file

test -d /etc/shadow && echo Oops, that file is a directory

test -r /etc/shadow && echo I can read the file

test -w /etc/shadow && echo I can write the file

See the test man page for other possibilities.

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How to read backward from the end of file in less or more

I'm sure someone else has a better answer, but

With "less" after you've opened the file:

G goes to the bottom of the file

^b goes up one page

? searches backwards.

As you said, you can open the file with +G and then use ? and ^b to scroll up. There are likely clever awk things you can do to achieve the same thing in a script.

Linux – Default permission for newly-created files/folders using ACLs not respected by commands like “unzip”

This behavior is the ACL_MASK at work. Looking at the index.php file, it does theoretically get the intended permission group:sharedusers:rwx, but effectively another one #effective:r--. This is because the theoretic value gets XOR'd with the mask::r-- to give the effective one, which is what you see with ls -l (or ll).

Now the ACL_MASK of mask::r-- is in fact a security feature of ACL, keeping you from giving access where you didn't intend to: When adding an existing file (as opposed to creating a new one), ACL sets the ACL_MASK to the former value of the file, which in this case was r--.

This isn't limited to unzip. This applies whenever you add a file as opposed to create it. You could try cp or tar for example, and would end up with the same result.

In fact the documentation (man 5 acl) states in the paragraph OBJECT CREATION AND DEFAULT ACLs that the default values only apply for object created with any of the following system calls: creat(), mkdir(), mknod(), mkfifo(), or open().

Therefore I can't give you a good solution, as you won't be able to use the ACL default mechanism for what you're doing.

Best Answer

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How to read backward from the end of file in less or more

Linux – Default permission for newly-created files/folders using ACLs not respected by commands like “unzip”

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