JSONPath Regex Filter — Pattern Matching in Filters

Regex Filters in JSONPath

Some JSONPath implementations support regular expression matching inside filter expressions using the =~ operator. This lets you select elements whose string properties match a pattern, providing powerful text-based filtering.

Syntax

$.array[?(@.property =~ /pattern/flags)]

The regex is enclosed in forward slashes, with optional flags after the closing slash:

• i — case-insensitive
• g — global (rarely needed in filters)
• m — multiline

Example

Given:

{
  "files": [
    { "name": "report-2024-01.pdf", "size": 1024 },
    { "name": "image-001.png", "size": 2048 },
    { "name": "report-2024-02.pdf", "size": 512 },
    { "name": "data-export.csv", "size": 4096 },
    { "name": "Report-Summary.PDF", "size": 768 }
  ]
}

• $.files[?(@.name =~ /report.*\.pdf/i)] returns all three report files, including "Report-Summary.PDF" (case-insensitive).
• $.files[?(@.name =~ /^image/)] returns only "image-001.png".
• $.files[?(@.name =~ /\.(csv|pdf)$/i)] returns all CSV and PDF files.

Common Regex Patterns in JSONPath

Pattern	Matches
/^prefix/	Strings starting with "prefix"
/suffix$/	Strings ending with "suffix"
/\d{4}-\d{2}/	Date-like patterns (YYYY-MM)
/^[A-Z]/	Strings starting with uppercase
/error|warning/i	"error" or "warning" (case-insensitive)

Implementation Support

Regex filters are not part of the original JSONPath specification by Stefan Goessner. Support varies:

• Jayway JsonPath (Java): Full regex support with =~
• jsonpath-plus (JavaScript): Supports regex via =~
• Python jsonpath-ng: Limited regex support
• RFC 9535 (IETF JSONPath): Does not include regex as a standard operator

Always check your library's documentation before relying on regex filters in production.

Alternatives When Regex Is Not Available

If your JSONPath implementation does not support regex, you can:

1. Extract all values with a wildcard and filter in application code.
2. Use string comparison operators for prefix/suffix matching where possible.
3. Pre-process the JSON data to add computed boolean fields.