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Available inall subroutines.

Looks up the key key in the table ID. When the key is present, its associated value will be returned. When the key is absent, a not set string value is returned.

You can use table.contains to check for the presence of a key. If you plan to do a lookup of that key's value, consider combining the calls into a single lookup to find the key's presence and the stored value at the same time. For example:

# note this depends on using a header, not a STRING variable
set req.http.x = table.lookup(t, "key");
if (!req.http.x) { # equivalent to if (!table.contains(t, "key"))
  # no such key
} else {
  # use the value of req.http.x
}

This works because a not set header compares false in conditions. The condition above depends on using a header for the returned value and not a local STRING variable. This is because a not set value is converted to an empty string when assigned to a STRING variable and the empty string always compares true in conditions. See VCL Types for details of the type conversion.

When a third STRING argument is provided, the lookup function behaves as it would normally, except when a key is absent, the default value is returned instead.

Examples

table geoip_lang {
  "US": "en-US",
  "FR": "fr-FR",
  "NL": "nl-NL",
}
if (!req.http.Accept-Language) {
  set req.http.Accept-Language = table.lookup(geoip_lang, client.geo.country_code, "en-US");
}

table extension {
  "xhtml5": "xhtml",
  "html5": "html",
  "htm": "html",
  "aif": "aiff",
  "tif": "tiff",
  "jpg": "jpeg",
  "mpg": "mpeg",
}

sub vcl_recv {
  # normalizing URL file extensions
  declare local var.ext STRING;

  # lowercase for both the table key and for the default value
  set var.ext = std.tolower(req.url.ext);
  set var.ext = table.lookup(extension, var.ext, var.ext);
}

Try it out

table.lookup is used in the following code examples. Examples apply VCL to real-world use cases and can be deployed as they are, or adapted for your own service. See the full list of code examples for more inspiration.

Click RUN on a sample below to provision a Fastly service, execute the code on Fastly, and see how the function behaves.