DIALRULES(5)

🌸 NAME 🌸

dialrules — HylaFAX dial string processing rules

okay bestie so this is the DIALRULES(5) page, filed under File Formats Manual, and it's literally about how HylaFAX takes the phone number you typed and turns it into something a modem can actually dial. sit with me, it's giving very "secret language of fax machines" and I'm obsessed 💅

---

✨ DESCRIPTION ✨

so a dial string is just... how to dial the telephone so you reach the destination facsimile machine, or some similar device. a user supplies this string with every outgoing facsimile job. simple enough right? wrong. because the HylaFAX server processes need to process user-supplied dial strings in two ways:

1. to craft a canonical phone number for use in locating the receiver's capabilities, and
2. to process it into a form suitable for sending to a modem.

and on top of that, client applications may also need to process a dial string to formulate an external form that does not include private information such as a credit card access code. (yes, credit card access codes, we love a 1996 moment 😭)

Phone number canonicalization and dial string preparation are done according to dial string processing rules that live in a file specified in the server configuration file — see the DialStringRules parameter in hylafax-config(5). and the generation of an externalized form for a dial string is done by rules that optionally appear in /etc/hylafax/dialrules on client machines. 🫶

A dial string rules file is an ASCII file containing one or more rule sets. A rule set defines a set of transformation rules that are sequentially applied to a dial string. Each rule set is associated with an identifier, with certain well-known identifiers being used by the facsimile server or client application. Each transformation rule is a regular expression and a replacement string; the regular expression is repeatedly applied to a dial string and any matching substring is replaced by the replacement string. periodt. 💖

---

🎀 the syntax, bestie 🎀

The syntax of a dial string rules file is as follows. Comments are introduced with the ! character and continue to the end of the current line. Identifiers are formed from a leading alphabetic and any number of subsequent alpha-numeric characters. A rule set is of the form:

Identifier := [
    rule1
    rule2
    ...
]

where rule1, rule2, and so on are transformation rules. Line breaks are significant. The initial rule set definition line and the trailing ] must be on separate lines; and each transformation rule must also be on a single line. no cap, it's that picky 🙈

Transformation rules are of the form:

regular-expression = replacement

where regular-expression is a POSIX 1003.2 extended regular expression and replacement is a string that is substituted in place of any portion of the dial string that is matched by the regular-expression. White space is significant in parsing transformation rules. If a regular expression or replacement string has embedded white space in it, then the white space needs to be escaped with a \ character or the entire string should be enclosed in quote (") marks. Replacement strings may reference the entire string matched by the regular expression with the & character. Substrings matched with the (...) constructs may be referenced by using \n where n is a single numeric digit between 1 and 9 that refers to the n-th matched substring; c.f. re_format(7), sed(1), etc. ✨

---

🦋 variables, because of course 🦋

To simplify and parameterize the construction of rule sets, dial string rules files may also include simple text-oriented variable definitions. A line of the form:

foo=string

defines a variable named foo that has the value string. String values with embedded whitespace must use the \ character or be enclosed in quote marks. Variables are interpolated into transformation rules by referencing them as:

${var}

Note that variable interpolation is done only once, at the time a transformation rule is defined. This means that forward references are not supported and that circular definitions will not cause loops. 💀

The facsimile server automatically defines four variables to have the values defined in its configuration file: AreaCode, CountryCode, LongDistancePrefix, and InternationalPrefix. These variables are initialized before parsing a dial string rules file; thus if they are defined in the rules file then they will override any definition by the server. 👑

---

👑 the three iconic rule set names 👑

There are three well known rule set names:

• CanonicalNumber — to convert a dial string to a canonical format
• DialString — to prepare a dial string before using it to dial the telephone
• DisplayNumber — to convert a dial string to an external "displayable" form that does not include the private information that might appear in the raw dial string

main character energy, all three of them 💅

---

🔥 EXAMPLES 🔥

This is the default set of rules for transforming a dial string into a canonical phone number:

Area=${AreaCode}                  ! local area code
Country=${CountryCode}            ! local country code
IDPrefix=${InternationalPrefix}   ! prefix for placing an international call
LDPrefix=${LongDistancePrefix}    ! prefix for placing a long distance call
!
! Convert a phone number to a canonical format:
!
!    +<country><areacode><rest>
!
! by (possibly) stripping off leading dialing prefixes for
! long distance and/or international dialing.
!
CanonicalNumber := [
%.*               =                          ! strip calling card stuff
[abcABC]          = 2                        ! these convert alpha to numbers
[defDEF]          = 3
[ghiGHI]          = 4
[jklJKL]          = 5
[mnoMNO]          = 6
[prsPRS]          = 7
[tuvTUV]          = 8
[wxyWXY]          = 9
[^+0-9]+          =                          ! strip white space etc.
^${IDPrefix}      = +                        ! replace int. dialing code
^${LDPrefix}      = +${Country}              ! replace l.d. dialing code
^[^+]             = +${Country}${Area}&      ! otherwise, insert canon form
]

okay let's walk through it because this is genuinely so satisfying:

• The first rule simply strips anything following a %; this will remove any calling card-related information.
• The next eight rules convert upper and lower case alphabetics to the equivalent key numbers (this is convenient for users that use mnemonic phone numbers).
• The tenth rule removes everything but numbers and plus signs.
• The eleventh rule translates any explicit international dialing prefix into the + symbol used to identify country codes.
• The twelfth rule replaces a leading long distance dialing prefix with the local country code string.
• The last rule matches local phone numbers and inserts the local country code and area code.

---

As an example, assume that

AreaCode=415
CountryCode=1
InternationalPrefix=011
LongDistancePrefix=1

then if the above set of rules is applied to 01123965-Tube%2345, the transformations would be:

01123965-Tube%2345    01123965-Tube    ! strip calling card stuff
01123965-Tube         01123965-8823    ! convert alphabetics
01123965-8823         011239658823     ! strip white space etc.
011239658823          +239658823       ! replace int. dialing code
+239658823            +239658823       ! replace l.d. dialing code
+239658823            +239658823       ! otherwise, insert canon form

for a final result of +239658823. like... it ATE and left no crumbs 🍓✨

---

🌈 SEE ALSO 🌈

sendfax(1), dialtest(8), faxq(8), faxsend(8), faxgetty(8), hylafax-config(5)

---

and that's the whole vibe bestie 🎀 this page is from May 8, 1996 and belongs to DIALRULES(5) in the File Formats Manual — yes it's older than us and it still understood the assignment. go forth and canonicalize your phone numbers, iykyk 💜🦋