Log File Highlighter

Description

A Visual Studio Code extension for adding color highlighting to log files. It is based on standard conventions for log4net log files but it's general enough to be useful for other variations of log files as well. The colors are customizable but by default the current color theme's colors are used.

Open Source

This extension is open source under the MIT License and completely free but if you like it and want to encourage further development, then you might want to consider supporting it using one of the links below:

But that's completely optional, of course 😊

Note

An earlier version of the syntax highlighting definition from this extension was included into Visual Studio Code version 1.20. If the default behavior of log files in VS Code is good enough for you, then you don't need this extension. However, if you want additional highlighting, customizable patterns and time duration calculation and visualization, then keep reading :-)

Features

Syntax Highlighting

The extension associates with .log files and applies coloring to the different elements in the file, for example:

Visualization of Time Duration and Progress

If you select multiple lines of a .log file, some simple timestamp analysis is performed.

• A status bar item is displayed that indicates how many days, hours, minutes, seconds and milliseconds that is selected.
• A progress bar is also drawn under the timestamps in the selection to give a visual representation of each line's point in time within the selection.
• Press Escape to clear the progress bars.

Settings

• enableProgressIndicator can be used to disable the progress indicator feature. The default value is true. Set it to false to disable the feature.

• progressIndicatorUnderlineColor can be used to set the color of the progress indicator. The default value is #00ff1f8f. Note the alpha channel value at the end of the color value (8f). This can be used to make the color semi-transparent for mixing with the background color.

Example:

"logFileHighlighter.enableProgressIndicator": true,
"logFileHighlighter.progressIndicatorUnderlineColor": "#ffee00",

Tail Mode

The extension also supports a tail mode where the end of the log file is kept in view as new lines are added. To activate it, scroll to the end of the log file until a message is shown in the status bar: Log File Tail Mode

To deactivate tail mode for the current file, scroll up again.

This feature can be disabled by setting the logFileHighlighter.enableTailMode setting to false.

Customization

Customizing the colors

By default, this extension reuses existing theme colors in order to adapt to the user's preferences. Sometimes this will result in colors that may not make complete sense in the log file context (for example ERROR might be green and DEBUG red, when it would be more appropriate to have it the other way around).

For this reason, the extension defines a special set of grammar tokens that can be used to override the colors of the default log items:

log.constant
log.date
log.debug
log.error
log.exception
log.exceptiontype
log.info
log.string
log.verbose
log.warning

To override the color for one of these, use the editor.tokenColorCustomizations user setting, which was introduced in Visual Studio Code 1.15. Here's an example that forces errors to be red and bold and warnings to be orange, regardless of what color theme is used:

"editor.tokenColorCustomizations": {
    "textMateRules": [
        {
            "scope": "log.error",
            "settings": {
                "foreground": "#af1f1f",
                "fontStyle": "bold"
            }
        },
        {
            "scope": "log.warning",
            "settings": {
                "foreground": "#f4ad42",
                "fontStyle": ""
            }
        }
    ]
}

Defining custom highlighting patterns

The extension also supports defining custom patterns to be highlighted. This can be useful to make the extension compatible with the log levels of an otherwise unsupported logging framework or to highlight domain specific patterns, or just about anything else.

The patterns are defined in the user settings like in this example:

"logFileHighlighter.customPatterns": [
    // Highlight the text 'Verbose' with green color
    {
        "pattern": "Verbose",
        "foreground": "#22aa22"
    },
    // Highlight the text 'E/' and any immediately following word constitient characters with red foreground and yellow background
    {
        "pattern": "E/\\w+",
        "foreground": "#af1f1f",
        "background": "#f3f38d"
    },
    // Highlight anything between square brackets with dark grey background
    {
        "pattern": "\\[(.*?)\\]",
        "background": "#333333"
    },
    // Highlight ERROR if surrounded by double quotes using positive lookbehind and lookahead expressions
    {
        "pattern": "(?<=\")ERROR(?=\")",
        "foreground": "#00FF00",
    }
]

Note: Both foreground and background are optional individually but at least one of them must be set for the custom pattern to be activated.

Tips

File associations

To make VS Code treat other file extensions than the default .log as log files, add the following to the user settings:

"files.associations": {
    "*.log.*": "log"
},

The example above associates extensions such as .log.1 and .log.2 with the Log File highlighter extension.

Custom pattern tips

Multiple styles for the same pattern

The same pattern can be used in multiple style configurations, which can be useful if you want to highlight the same pattern in different ways. Example:

{
    "pattern": "todo",
    "patternFlags": "i",
    "foreground": "#000000",
    "background": "#7d8aff",
},
{
    "pattern": "todo",
    "patternFlags": "i",
    "highlightEntireLine": true,
    "background": "#7d8aff50",
},

Case sensitivity

The custom patterns are case sensitive by default. To make a pattern case-insensitive, set patternFlags to "i".

Here's and example that matches both "todo" and "TODO":

{
    "pattern": "todo",
    "patternFlags": "i",
    "foreground": "#ff0000"
},

Multiline custom patterns

The custom patterns can be multiline patterns. This can be useful for example when you want to highlight SQL statements, stack traces, etc. To match multiple lines, use the s flag in the patternFlags setting. This flag makes the . character match newline characters as well. Here is an example that highlights SQL statements:

{
    "pattern": "SELECT.*?FROM.*?WHERE.*?$",
    "patternFlags": "si",
    "foreground": "#eeff05",
},

Notes:

• The patternFlags setting is used to set the s flag which makes the . character match newline characters (and i for case insensitivity).
• The pattern uses ? after the * quantifier to make the match non-greedy. This is important to make the pattern match only one SQL statement at a time and not extend to the next WHERE clause of a later log entry.

Result:

Syntax highlighting of large files

VS Code disables color highlighting for large files by default. This can be disabled with the editor.largeFileOptimization setting. To enable highlighting for large log files without changing the setting for other file types, place it in the [log] scope like this:

"[log]": {
    "editor.largeFileOptimizations": false,
}