chmod-calc

# chmod Calculator Convert file permission specifications between numeric (octal) and symbolic notation, and produce the corresponding `chmod` command. ## Input - Either a numeric permission string (e.g. `755`, `644`, `4755`) - Or a description of permissions per entity (owner/group/others with read/write/execute) - Or a symbolic string (e.g. `rwxr-xr-x`) ## Output - Numeric notation (3 or 4 digits) - Symbolic notation (9 characters, e.g. `rwxr-xr-x`) - Numeric chmod command: `chmod 755 filename` - Symbolic chmod command: `chmod u+rwx,g+rx,o+rx filename` - Plain-English description of what each entity can do ## Instructions ### Permission bit values Each entity (owner/group/others) is a sum of: - Read (r) = 4 - Write (w) = 2 - Execute (x) = 1 ### Special permission bits (4th leading digit) - Setuid = 4 (runs as owner) - Setgid = 2 (runs as group) - Sticky = 1 (only owner can delete in directory) ### Numeric → Symbolic conversion Given a 3-digit octet `OGO`: - For each digit, decompose: `r` if bit 2 set, `w` if bit 1 set, `x` if bit 0 set, else `-`. - With leading special digit `S`: setuid sets `s/S` in owner execute position; setgid sets `s/S` in group execute position; sticky sets `t/T` in others execute position. ### Symbolic → Numeric conversion Map each 3-char group to a digit using the bit values above. ### Symbolic chmod command format Build clauses for each entity with permissions set: - `u` = owner, `g` = group, `o` = others - Emit `{entity}+{perms}` for each entity that has any permissions - Special bits: `u+s` (setuid), `g+s` (setgid), `+t` (sticky) ### Common permission reference | Numeric | Symbolic | Description | |---------|-------------|--------------------------------| | 644 | rw-r--r-- | Standard file (owner rw, rest r) | | 755 | rwxr-xr-x | Standard directory/executable | | 600 | rw------- | Private file (owner only) | | 700 | rwx------ | Private directory/executable | | 777 | rwxrwxrwx | Full access (avoid in production) | | 4755 | rwsr-xr-x | Setuid executable | | 2755 | rwxr-sr-x | Setgid executable | | 1755 | rwxr-xr-t | Sticky directory | ## Options - Input can be numeric, symbolic, or a plain-English description of desired permissions. ## Examples **Input:** `755` **Output:** ``` Numeric: 755 Symbolic: rwxr-xr-x Command (numeric): chmod 755 filename Command (symbolic): chmod u+rwx,g+rx,o+rx filename Owner: read, write, execute Group: read, execute Others: read, execute ``` **Input:** `644` **Output:** ``` Numeric: 644 Symbolic: rw-r--r-- Command (numeric): chmod 644 filename Command (symbolic): chmod u+rw,g+r,o+r filename Owner: read, write Group: read Others: read ``` **Input:** `rwxr-xr-x` **Output:** ``` Numeric: 755 Symbolic: rwxr-xr-x Command (numeric): chmod 755 filename Command (symbolic): chmod u+rwx,g+rx,o+rx filename ``` **Input:** "owner can read and write, group can read, others nothing" **Output:** ``` Numeric: 640 Symbolic: rw-r----- Command (numeric): chmod 640 filename Command (symbolic): chmod u+rw,g+r filename ``` ## Error Handling - If numeric input has more than 4 digits or contains non-octal characters, say so. - If a digit in the octet exceeds 7, explain that each permission digit must be 0–7. - If symbolic input is not exactly 9 or 10 characters in valid format, ask for clarification. - Warn the user if they request `777` that this allows full access to everyone and is a security risk.