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jpayne@68: GNU libtextstyle: 1. Introduction
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jpayne@68: [Top] |
jpayne@68: [Contents] |
jpayne@68: [Index] |
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jpayne@68: Text is easier to read when it is accompanied with styling information,
jpayne@68: such as color, font attributes (weight, posture), or underlining, and
jpayne@68: this styling is customized appropriately for the output device.
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jpayne@68: GNU libtextstyle provides an easy way to add styling to programs that
jpayne@68: produce output to a console or terminal emulator window. It does this
jpayne@68: in a way that allows the end user to customize the styling using the
jpayne@68: industry standard, namely Cascading Style Sheets (CSS).
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jpayne@68: Let's look at the traditional way styling is done for specific programs.
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jpayne@68: Browsers, when they render HTML, use CSS styling.
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jpayne@68: The older approach to user-customizable text styling is that the user
jpayne@68: associates patterns with escape sequences in an environment variable or a
jpayne@68: command-line argument. This is the approach used, for example, by the
jpayne@68: GNU ‘ls’ program in combination with the ‘dircolors’ program.
jpayne@68: The processing is distributed across several steps:
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jpayne@68: There is default style definition that is hard-coded in the
jpayne@68: ‘dircolors’ program. The user can also define their own definitions
jpayne@68: in a file such as ‘~/.dir_colors’. This style definition contains
jpayne@68: explicit terminal escape sequences; thus, it can only be used with
jpayne@68: consoles and terminal emulators, and each style definition applies only
jpayne@68: to a certain class of mostly-compatible terminal emulators.
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dircolors program, when invoked, translates such a style
jpayne@68: definition to a sequence of shell statements that sets an environment
jpayne@68: variable LS_COLORS.
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jpayne@68: The shell executes these statements, and thus sets the environment
jpayne@68: variable
LS_COLORS.
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jpayne@68: The program looks at the environment variable and emits the listed escape
jpayne@68: sequences.
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jpayne@68: In contrast, this library implements styling as follows:
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jpayne@68: There is a default style definition in a CSS file that is part of the
jpayne@68: same package as the stylable program. The user can also define their own
jpayne@68: definitions in a CSS file, and set an environment environment variable to
jpayne@68: point to it.
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jpayne@68: The program looks at the environment variable, parses the CSS file,
jpayne@68: translates the styling specifications to the form that is appropriate for
jpayne@68: the output device (escape sequences for terminal emulators, inline CSS
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<span> elements for HTML output), and emits it.
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jpayne@68: Thus, with GNU libtextstyle, the styling has the following properties:
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jpayne@68: It is easier for the user to define their own styling, because the file
jpayne@68: format is standardized and supported by numerous syntax aware editors.
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jpayne@68: A styling file does not depend on the particular output device. An HTML
jpayne@68: output and a black-on-white terminal emulator can use the same styling
jpayne@68: file. A white-on-black (or even green-on-black) terminal emulator will
jpayne@68: need different styling, though.
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jpayne@68: It is simpler: There is no need for a program that converts the style
jpayne@68: specification from one format to another.
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jpayne@68: There are generally two approaches for adding styling to text:
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jpayne@68: The program that generates the text adds the styling. It does so through
jpayne@68: interleaved statements that turn on or off specific attributes.
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jpayne@68: The styling gets added by a separate program, that postprocesses the
jpayne@68: output. This separate program usually uses regular expressions to
jpayne@68: determine which text regions to style with a certain set of text
jpayne@68: attributes.
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jpayne@68: The first approach produces a styling that is 100% correct, regardless of
jpayne@68: the complexity of the text that is being output. This is the preferred
jpayne@68: approach for example for JSON, XML, or programming language text.
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jpayne@68: The second approach works well if the output has a simple, easy-to-parse
jpayne@68: format. It may produce wrong styling in some cases when the text format
jpayne@68: is more complex. This approach is often used for viewing log files.
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jpayne@68: GNU libtextstyle supports both approaches; it includes an example program
jpayne@68: for each of the two approaches.
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jpayne@68: | [ << ] |
jpayne@68: [ >> ] |
jpayne@68: |
jpayne@68: |
jpayne@68: |
jpayne@68: |
jpayne@68: |
jpayne@68: [Top] |
jpayne@68: [Contents] |
jpayne@68: [Index] |
jpayne@68: [ ? ] |
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jpayne@68: This document was generated by Bruno Haible on February, 21 2024 using texi2html 1.78a.
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