Is there a web based converter between rwx and the octal version?

Question

I can never remember what the conversion is from something like rw-r--r-- to 644. Is there a simple web based converter between the 2?

Answer 1

http://permissions-calculator.org/

Answer 2

Why do you need octal number in the first place?

I always use:

chmod o+x file   # all + eXecute permissions
chmod g-w file   # group - write perms
chmod u=r file   # user can just read
chmod ug=rw file # user,group = read and write
chmod a+w file   # user,group,others + write 

ugo(a) is easy to remember. However you can confuse o:=owner? o:=other? but what would be u, if o=owner? u:=user, therefore o=other.

Some comands like numerical permissions only. Okay, it's not hard to calculate, if you remember the two sequences: ugo + rwx.

    r   w   x  | Sum
u   4   2   1  | 7
g   4   -   1  |  5
o   4   2   -  |   6
---------------------
                 756

Yes, very artificial.

When it comes to s and S I have to consult the manual. Maybe google next time. :)

Answer 3

I have this little alias that you can put in your .bashrc (or equivalent).

DISCLAIMER: I am not the author of the script, and I'm not sure who wrote it... but props to him/her for doing this.

alias lsp = "ls -l --color | 
      awk '{k=0; for(i=0;i<=8;i++) k+=((substr(\$1,i+2,1)~/[rwx]/)*2^(8-i));
      if (k) printf(\" %0o \",k); print}'"

Answer 4

Octal is used for permissions because it's an easy conversion. Each group of rwx forms one octal digit. All you have to remember is the first 3 powers of 2: 4, 2, 1. r = 4, w = 2, x = 1.

rw-r--r-- = 110 100 100 = 4+2+0 4+0+0 4+0+0 = 644