Build and reuse a pattern

Build a pattern once and reuse it

Mark the fields in one line, let trex build the pattern that extracts them from every line of that shape, save it as a pattern file, and read new input with it from then on.

Build it from a marked line

Write each value to extract as {name:text}, with [int] or another type before the name where the value has one. The other lines are examples the pattern must also read:

$ trex infer --mark 'GET https://{host:example.com}/a {[int]code:200}' 'GET https://trex.dev/b 404' --lib-file
# Built by trex infer from 2 lines in 1 shape; `extract` names every shape in order.
let extract_1 = ^ "GET" (\U):host (\N):code ~<($ .)
let extract = \{extract_1}
fields extract {host:host} {[int]code}
test extract accepts "GET https://example.com/a 200"

use trex::infer::build::{Mint, Spec, build};

let marked = trex::infer::marks::parse_lines("GET https://{host:example.com}/a {[int]code:200}").expect("valid marks");
let lines = ["GET https://trex.dev/b 404".to_string()];
let shapes = trex::ShapeSet::new();
let spec = Spec { lines: &lines, marked: &marked, hints: &[], counters: &[], shapes: &shapes, unanchored: false, mint: Mint::Inline };
let file = build(&spec).expect("a pattern").file();
assert!(file.contains("fields extract {host:host} {[int]code}"));

>>> import trex
>>> built = trex.infer(["GET https://trex.dev/b 404"], marked=["GET https://{host:example.com}/a {[int]code:200}"])
>>> print(built.file, end="")
# Built by trex infer from 2 lines in 1 shape; `extract` names every shape in order.
let extract_1 = ^ "GET" (\U):host (\N):code ~<($ .)
let extract = \{extract_1}
fields extract {host:host} {[int]code}
test extract accepts "GET https://example.com/a 200"

PS> $built = ConvertTo-TrexPattern -Example 'GET https://trex.dev/b 404' -Marked 'GET https://{host:example.com}/a {[int]code:200}'
PS> $built.File
# Built by trex infer from 2 lines in 1 shape; `extract` names every shape in order.
let extract_1 = ^ "GET" (\U):host (\N):code ~<($ .)
let extract = \{extract_1}
fields extract {host:host} {[int]code}
test extract accepts "GET https://example.com/a 200"

{host:host} reads the host of the URL the field holds. The fields line keeps each field’s name, type and accessor beside the pattern; PowerShell casts a field to its [type], and the other surfaces give its text.

Save it and read with it

Save that text as hosts.trex, then read new lines with \{extract}:

$ cat hosts.trex
let extract_1 = ^ "GET" (\U):host (\N):code ~<($ .)
let extract = \{extract_1}
fields extract {host:host} {[int]code}

$ trex scan '\{extract}' --lib hosts.trex --text 'GET https://example.org/x 500' --fields
record  lines  host         code
1       1      example.org  500

use trex::infer::build::{fields_for, read_records};

let mut shapes = trex::ShapeSet::new();
shapes.declare_text("let extract_1 = ^ \"GET\" (\\U):host (\\N):code ~<($ .)\nlet extract = \\{extract_1}\nfields extract {host:host} {[int]code}").expect("a pattern file");
let pattern = trex::parser::parse_with_shapes(r"\{extract}", &shapes).expect("valid pattern");
let fields = fields_for(r"\{extract}", &pattern, &shapes);
let records = read_records(&fields, &pattern, &shapes, "GET https://example.org/x 500").expect("records");
let host = fields.iter().position(|f| f.name == "host").expect("a host field");
assert_eq!(records[0].values[host].as_ref().expect("a host").joined(), "example.org");

Lines of several layouts build one branch a layout; a pattern that extracts fields has the marks, lists, records and declared shapes a build reads.

Query records