state_at_end: Utilities for Managing CSI and OSC State In Strings

In fansi: ANSI Control Sequence Aware String Functions

Utilities for Managing CSI and OSC State In Strings

Description

state_at_end reads through strings computing the accumulated SGR and OSC hyperlinks, and outputs the active state at the end of them. close_state produces the sequence that closes any SGR active and OSC hyperlinks at the end of each input string. If normalize = FALSE (default), it will emit the reset code "ESC[0m" if any SGR is present. It is more interesting for closing SGRs if normalize = TRUE. Unlike state_at_end and other functions close_state has no concept of carry: it will only emit closing sequences for states explicitly active at the end of a string.

Usage

state_at_end(
  x,
  warn = getOption("fansi.warn", TRUE),
  term.cap = getOption("fansi.term.cap", dflt_term_cap()),
  normalize = getOption("fansi.normalize", FALSE),
  carry = getOption("fansi.carry", FALSE)
)

close_state(
  x,
  warn = getOption("fansi.warn", TRUE),
  normalize = getOption("fansi.normalize", FALSE)
)

Arguments

x	a character vector or object that can be coerced to such.
warn	TRUE (default) or FALSE, whether to warn when potentially problematic Control Sequences are encountered. These could cause the assumptions fansi makes about how strings are rendered on your display to be incorrect, for example by moving the cursor (see ?fansi). At most one warning will be issued per element in each input vector. Will also warn about some badly encoded UTF-8 strings, but a lack of UTF-8 warnings is not a guarantee of correct encoding (use validUTF8 for that).
term.cap	character a vector of the capabilities of the terminal, can be any combination of "bright" (SGR codes 90-97, 100-107), "256" (SGR codes starting with "38;5" or "48;5"), "truecolor" (SGR codes starting with "38;2" or "48;2"), and "all". "all" behaves as it does for the ctl parameter: "all" combined with any other value means all terminal capabilities except that one. fansi will warn if it encounters SGR codes that exceed the terminal capabilities specified (see term_cap_test for details). In versions prior to 1.0, fansi would also skip exceeding SGRs entirely instead of interpreting them. You may add the string "old" to any otherwise valid term.cap spec to restore the pre 1.0 behavior. "old" will not interact with "all" the way other valid values for this parameter do.
normalize	TRUE or FALSE (default) whether SGR sequence should be normalized out such that there is one distinct sequence for each SGR code. normalized strings will occupy more space (e.g. "\033[31;42m" becomes "\033[31m\033[42m"), but will work better with code that assumes each SGR code will be in its own escape as crayon does.
carry	TRUE, FALSE (default), or a scalar string, controls whether to interpret the character vector as a "single document" (TRUE or string) or as independent elements (FALSE). In "single document" mode, active state at the end of an input element is considered active at the beginning of the next vector element, simulating what happens with a document with active state at the end of a line. If FALSE each vector element is interpreted as if there were no active state when it begins. If character, then the active state at the end of the carry string is carried into the first element of x (see "Replacement Functions" for differences there). The carried state is injected in the interstice between an imaginary zeroeth character and the first character of a vector element. See the "Position Semantics" section of substr_ctl and the "State Interactions" section of ?fansi for details. Except for strwrap_ctl where NA is treated as the string "NA", carry will cause NAs in inputs to propagate through the remaining vector elements.

Value

character vector same length as x.

Control and Special Sequences

Control Sequences are non-printing characters or sequences of characters. Special Sequences are a subset of the Control Sequences, and include CSI SGR sequences which can be used to change rendered appearance of text, and OSC hyperlinks. See fansi for details.

Output Stability

Several factors could affect the exact output produced by fansi functions across versions of fansi, R, and/or across systems. In general it is best not to rely on exact fansi output, e.g. by embedding it in tests.

Width and grapheme calculations depend on locale, Unicode database version, and grapheme processing logic (which is still in development), among other things. For the most part fansi (currently) uses the internals of base::nchar(type='width'), but there are exceptions and this may change in the future.

How a particular display format is encoded in Control Sequences is not guaranteed to be stable across fansi versions. Additionally, which Special Sequences are re-encoded vs transcribed untouched may change. In general we will strive to keep the rendered appearance stable.

To maximize the odds of getting stable output set normalize_state to TRUE and type to "chars" in functions that allow it, and set term.cap to a specific set of capabilities.

See Also

?fansi for details on how Control Sequences are interpreted, particularly if you are getting unexpected results, unhandled_ctl for detecting bad control sequences.

Examples

x <- c("\033[44mhello", "\033[33mworld")
state_at_end(x)
state_at_end(x, carry=TRUE)
(close <- close_state(state_at_end(x, carry=TRUE), normalize=TRUE))
writeLines(paste0(x, close, " no style"))

fansi documentation built on Oct. 9, 2023, 1:07 a.m.