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: INLINECODE6
• Symbolic chmod command: INLINECODE7
• 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:
CODEBLOCK0

Input: 644
Output:
CODEBLOCK1

Input: rwxr-xr-x
Output:
CODEBLOCK2

Input: "owner can read and write, group can read, others nothing"
Output:
CODEBLOCK3

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.