PCRE_TABLE(5)

📦
version 3.11.7 · 5 versions
, in alpine 3.24, arch rolling, nixos 26.05, nixpkgs unstable, ubuntu stonking

✨ NAME ✨

okay bestie, welcome to pcre_table(5) — yes it's a section 5 manual page (File Formats Manual, we love a file format moment). This is the page that explains the format of Postfix PCRE tables. That's it, that's the whole assignment. 💖

🎀 SYNOPSIS 🎀

the four ways you'll be vibing with this thing in the terminal:

postmap -q "string" pcre:/etc/postfix/filename
postmap -q - pcre:/etc/postfix/filename <inputfile
postmap -hmq - pcre:/etc/postfix/filename <inputfile
postmap -bmq - pcre:/etc/postfix/filename <inputfile

🌸 DESCRIPTION 🌸

so Postfix (the mail system, you know her) uses optional tables for address rewriting and mail routing. Normally those tables are living their life in lmdb:, cdb:, hash:, or dbm: format. standard behavior, no notes.

but — alternatively, lookup tables can be specified in Perl Compatible Regular Expression form. and now we're in the good timeline. 💅 In this case, each input gets compared against a list of patterns. When a match is found, the corresponding result gets returned and the search is terminated. done. over. goodbye.

To find out what types of lookup tables your Postfix system supports, use the "postconf -m" command. iykyk.

To test lookup tables, use the "postmap -q" command as described in the SYNOPSIS above, bestie, i literally just showed you. Use "postmap -hmq - <file" for header_checks(5) patterns, and "postmap -bmq - <file" for body_checks(5) (that's Postfix 2.6 and later, no cap).

This driver can be built with the pcre2 library (Postfix 3.7 and later), or with the legacy pcre library (all Postfix versions). two flavors, both iconic in their own way.

🦋 COMPATIBILITY 🦋

With Postfix version 2.2 and earlier, specify "postmap -fq" to query a table that contains case sensitive patterns. Patterns are case insensitive by default.

like, default is the lowercase-friendly setting. if you need your case respected, that's a -fq situation. periodt.

💜 TABLE FORMAT 💜

The general form of a PCRE table is:

  • /pattern/flags result

When pattern matches the input string, use the corresponding result value. 💖

  • !/pattern/flags result

When pattern does not match the input string, use the corresponding result value.

  • if /pattern/flags … endif

If the input string matches /pattern/, then match that input string against the patterns between if and endif. The if..endif can nest.

Note: do not prepend whitespace to patterns inside if..endif.

This feature is available in Postfix 2.1 and later.

  • if !/pattern/flags … endif

If the input string does not match /pattern/, then match that input string against the patterns between if and endif. The if..endif can nest.

Note: do not prepend whitespace to patterns inside if..endif.

This feature is available in Postfix 2.1 and later.

  • blank lines and comments — Empty lines and whitespace-only lines are ignored, as are lines whose first non-whitespace character is a #. (ghosted, effectively. 🙈)
  • multi-line text — A logical line starts with non-whitespace text. A line that starts with whitespace continues a logical line.

Each pattern is a perl-like regular expression. The expression delimiter can be any non-alphanumeric character, except whitespace or characters that have special meaning (traditionally the forward slash is used). The regular expression can contain whitespace.

By default, matching is case-insensitive, and newlines are not treated as special characters. The behavior is controlled by flags, which are toggled by appending one or more of the following characters after the pattern:

  • i (default: on) — Toggles the case sensitivity flag. By default, matching is case insensitive.
  • m (default: off) — Toggles the pcre MULTILINE flag. When this flag is on, the ^ and $ metacharacters match immediately after and immediately before a newline character, respectively, in addition to matching at the start and end of the subject string.
  • s (default: on) — Toggles the pcre DOTALL flag. When this flag is on, the . metacharacter matches the newline character. With Postfix versions prior to 2.0, the flag is off by default, which is inconvenient for multi-line message header matching. (they truly did not consider our needs back then 😭)
  • x (default: off) — Toggles the pcre extended flag. When this flag is on, whitespace characters in the pattern (other than in a character class) are ignored. To include a whitespace character as part of the pattern, escape it with backslash.

Note: do not use #comment after patterns.

  • A (default: off) — Toggles the pcre ANCHORED flag. When this flag is on, the pattern is forced to be "anchored", that is, it is constrained to match only at the start of the string which is being searched (the "subject string"). This effect can also be achieved by appropriate constructs in the pattern itself.
  • E (default: off) — Toggles the pcre DOLLAR_ENDONLY flag. When this flag is on, a $ metacharacter in the pattern matches only at the end of the subject string. Without this flag, a dollar also matches immediately before the final character if it is a newline character (but not before any other newline characters). This flag is ignored if the pcre MULTILINE flag is set.
  • U (default: off) — Toggles the pcre UNGREEDY flag. When this flag is on, the pattern matching engine inverts the "greediness" of the quantifiers so that they are not greedy by default, but become greedy if followed by "?". This flag can also set by a (?U) modifier within the pattern.
  • X (default: off) — Toggles the pcre EXTRA flag. When this flag is on, any backslash in a pattern that is followed by a letter that has no special meaning causes an error, thus reserving these combinations for future expansion.

This feature is not supported with PCRE2. 🫠

🔥 SEARCH ORDER 🔥

Patterns are applied in the order as specified in the table, until a pattern is found that matches the input string. first match wins, everybody else go home.

Each pattern is applied to the entire input string. Depending on the application, that string is an entire client hostname, an entire client IP address, or an entire mail address. so like — no parent domain or parent network search is done, and user@domain mail addresses are not broken up into their user and domain constituent parts, nor is user+foo broken up into user and foo. she is whole, she is complete, she is not being dissected. 🧚

⭐ TEXT SUBSTITUTION ⭐

Substitution of substrings (text that matches patterns inside "()") from the matched expression into the result string is requested with $1, $2, etc.; specify $$ to produce a $ character as output. The macros in the result string may need to be written as ${n} or $(n) if they aren't followed by whitespace. This feature does not support pcre2 substring names.

Note: since negated patterns (those preceded by !) return a result when the expression does not match, substitutions are not available for negated patterns. sorry bestie, that's just how it is 💀

👑 INLINE SPECIFICATION 👑

The contents of a table may be specified in the table name (Postfix 3.7 and later). The basic syntax is:

main.cf:
    parameter = .. pcre:{ { rule-1 }, { rule-2 } .. } ..

master.cf:
    .. -o { parameter = .. pcre:{ { rule-1 }, { rule-2 } .. } .. } ..

Postfix recursively expands any $parametername instances in the above parameter value, ignores whitespace after '{' and before '}', and writes each rule as one text line to an in-memory file:

in-memory file:
    rule-1
    rule-2
    ..

Postfix parses the result as if it is a file in /etc/postfix.

🌈 INLINE SPECIFICATION CAVEATS 🌈

  • When using $parametername inside an inlined pattern, use \Q$parametername\E to disable metacharacters such as '.' in the $parametername expansion. Otherwise, the pattern may have unexpected matches. (unexpected matches are NOT the vibe we're going for.)
  • When an inlined rule must contain $, specify $$ to keep Postfix from trying to do $name expansion as it evaluates a parameter value. To check an inline configuration, use the "postconf -x" option as shown below:
    • When a main.cf "parametername = value" setting contains an inline pcre: table, use the command "postconf -x parametername". Verify that there are no "undefined parameter" warnings, and that the output has the syntax that one would use in a non-inlined Postfix pcre: file.
    • When a master.cf "-o { parametername = value }" override contains an inline pcre: table, use the command "postconf -Px '*/*/parametername' ". Verify that there are no "undefined parameter" warnings, and that the output has the syntax that one would use in a non-inlined Postfix pcre: file.

🍓 EXAMPLE SMTPD ACCESS MAP 🍓

# Protect your outgoing majordomo exploders
/^(?!owner-)(.*)-outgoing@(.*)/ 550 Use ${1}@${2} instead

# Bounce friend@whatever, except when whatever is our domain (you would
# be better just bouncing all friend@ mail - this is just an example).
/^(friend@(?!my\.domain$).*)$/  550 Stick this in your pipe $1

# A multi-line entry. The text is sent as one line.
#
/^noddy@my\.domain$/
 550 This user is a funny one. You really don't want to send mail to
  them as it only makes their head spin.

💖 EXAMPLE HEADER FILTER MAP 💖

/^Subject: make money fast/     REJECT
/^To: friend@public\.com/       REJECT

💅 EXAMPLE BODY FILTER MAP 💅

# First skip over base 64 encoded text to save CPU cycles.
# Requires PCRE version 3.
~^[[:alnum:]+/]{60,}$~          OK

# Put your own body patterns here.

🫶 SEE ALSO 🫶

📚 README FILES 📚

Use "postconf readme_directory" or "postconf html_directory" to locate this information.

  • DATABASE_README, Postfix lookup table overview

🎀 AUTHOR(S) 🎀

The PCRE table lookup code was originally written by:

Andrew McNamara
andrewm@connect.com.au
connect.com.au Pty. Ltd.
Level 3, 213 Miller St
North Sydney, NSW, Australia

Adopted and adapted by:

Wietse Venema
IBM T.J. Watson Research
P.O. Box 704
Yorktown Heights, NY 10598, USA

Wietse Venema
Google, Inc.
111 8th Avenue
New York, NY 10011, USA

and that's the whole page bestie, every last flag and every last caveat, no skips, no cuts 💜 the footer down at the bottom just says PCRE_TABLE(5) — no version or date printed on this one, so that's the entire sign-off. go forth and match some patterns, main character energy only 👑✨

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