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

This site provides an interactive way to see what permissions bits are set when various bits are set/unset.

• http://permissions-calculator.org/

The "calculator" looks like this:

  

Answer 2

Why do you need an 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 commands 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

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

Answer 4

I like this permissions calculator:
http://file-permissions.ninja

Answer 5

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 6

This is by far the most convenient, and is besides I believe, exactly what you asked for originally:

http://ss64.com/osx/chmod.html

It is fully interactive, though you cannot edit the string "-r-x-------" but you can the octal or the checkboxes. Doing either updates the other.

From the same page:

Numeric (absolute) mode:

From one to four octal digits Any omitted digits are assumed to be leading zeros.

The first digit = selects attributes for the set user ID (4) and set group ID (2) and save text image (1) The second digit = permissions for the user who owns the file: read (4), write (2), and execute (1) The third digit = permissions for other users in the file's group: read (4), write (2), and execute (1) The fourth digit = permissions for other users NOT in the file's group: read (4), write (2), and execute (1)

The octal (0-7) value is calculated by adding up the values for each digit User (rwx) = 4+2+1 = 7 Group(rx) = 4+1 = 5 World (rx) = 4+1 = 5 chmod mode = 0755

Answer 7

Even though this is not a "web" calculator, since nico's answer does not handle setuid, setgid, and sticky indicators, but does get up-votes, an example of an updated scriptlet that handles the extra permissions states may be warranted:

ls -l | \
awk '{k=0; for(i=0; i<=8; i++) k+=((substr($1, i+2, 1) ~ /[rwxs]/)*2^(8-i));
     if ($1 ~ /^.{3}[Ss]/) k+=2048; if($1 ~ /^.{6}[Ss]/) k+=1024;
     if ($1 ~ /[Tt]/) k+=512; if(k) printf("%4o ",k); print; }'

This question is a better fit for scripted solutions where glenn jackman offers a perl stat one-liner similar to:

$ what="/tmp"
$ perl -s -e '@fields = stat "$f"; printf "%04o\n", $fields[2] & 07777' -- -f="$what"
1777

The awk script is based on one found here