Template functions

The text template format used in | line_format and | label_format support the usage of functions.

All labels are added as variables in the template engine. They can be referenced using they label name prefixed by a .(e.g .label_name). For example the following template will output the value of the path label:

{{ .path }}

You can take advantage of pipeline to join together multiple functions. In a chained pipeline, the result of each command is passed as the last argument of the following command.

Example:

{{ .path | replace " " "_" | trunc 5 | upper }}

ToLower and ToUpper

This function converts the entire string to lowercase or uppercase.

Signatures:

• ToLower(string) string
• ToUpper(string) string

Examples:

"{{.request_method | ToLower}}"
"{{.request_method | ToUpper}}"
`{{ToUpper "This is a string" | ToLower}}`

Note: In Loki 2.1 you can also use respectively lower and upper shortcut, e.g {{.request_method | lower }}.

Replace string

Note: In Loki 2.1 replace (as opposed to Replace) is available with a different signature but easier to chain within pipeline.

Use this function to perform a simple string replacement.

Signature:

Replace(s, old, new string, n int) string

It takes four arguments:

• s source string
• old string to replace
• new string to replace with
• n the maximun amount of replacement (-1 for all)

Example:

`{{ Replace "This is a string" " " "-" -1 }}`

The results in This-is-a-string.

Trim, TrimLeft, TrimRight, and TrimSpace

Note: In Loki 2.1 trim, trimAll, trimSuffix and trimPrefix have been added with a different signature for better pipeline chaining.

Trim returns a slice of the string s with all leading and trailing Unicode code points contained in cutset removed.

Signature: Trim(value, cutset string) string

TrimLeft and TrimRight are the same as Trim except that it trims only leading and trailing characters respectively.

`{{ Trim .query ",. " }}`
`{{ TrimLeft .uri ":" }}`
`{{ TrimRight .path "/" }}`

TrimSpace TrimSpace returns string s with all leading and trailing white space removed, as defined by Unicode.

Signature: TrimSpace(value string) string

{{ TrimSpace .latency }}

TrimPrefix and TrimSuffix will trim respectively the prefix or suffix supplied.

Signature:

• TrimPrefix(value string, prefix string) string
• TrimSuffix(value string, suffix string) string

{{ TrimPrefix .path "/" }}

regexReplaceAll and regexReplaceAllLiteral

regexReplaceAll returns a copy of the input string, replacing matches of the Regexp with the replacement string replacement. Inside string replacement, $ signs are interpreted as in Expand, so for instance $1 represents the text of the first sub-match. See the golang Regexp.replaceAll documentation for more examples.

`{{ regexReplaceAllLiteral "(a*)bc" .some_label "${1}a" }}`

regexReplaceAllLiteral function returns a copy of the input string and replaces matches of the Regexp with the replacement string replacement. The replacement string is substituted directly, without using Expand.

`{{ regexReplaceAllLiteral "(ts=)" .timestamp "timestamp=" }}`

You can combine multiple functions using pipe. For example, to strip out spaces and make the request method in capital, you would write the following template: {{ .request_method | TrimSpace | ToUpper }}.

lower

Added in Loki 2.1

Use this function to convert to lower case.

Signature:

lower(string) string

Examples:

"{{ .request_method | lower }}"
`{{ lower  "HELLO"}}`

The last example will return hello.

upper

Added in Loki 2.1

Use this function to convert to upper case.

Signature:

upper(string) string

Examples:

"{{ .request_method | upper }}"
`{{ upper  "hello"}}`

This results in HELLO.

title

Note: Added in Loki 2.1.

Convert to title case.

Signature:

title(string) string

Examples:

"{{.request_method | title}}"
`{{ title "hello world"}}`

The last example will return Hello World.

trunc

Note: Added in Loki 2.1.

Truncate a string and add no suffix.

Signature:

trunc(count int,value string) string

Examples:

"{{ .path | trunc 2 }}"
`{{ trunc 5 "hello world"}}`   // output: hello
`{{ trunc -5 "hello world"}}`  // output: world

substr

Note: Added in Loki 2.1.

Get a substring from a string.

Signature:

trunc(start int,end int,value string) string

If start is < 0, this calls value[:end]. If start is >= 0 and end < 0 or end bigger than s length, this calls value[start:] Otherwise, this calls value[start, end].

Examples:

"{{ .path | substr 2 5 }}"
`{{ substr 0 5 "hello world"}}`  // output: hello
`{{ substr 6 11 "hello world"}}` // output: world

replace

Note: Added in Loki 2.1.

This function performs simple string replacement.

Signature: replace(old string, new string, src string) string

It takes three arguments:

• old string to replace
• new string to replace with
• src source string

Examples:

{{ .cluster | replace "-cluster" "" }}
{{ replace "hello" "world" "hello world" }}

The last example will return world world.

trim

Note: Added in Loki 2.1.

The trim function removes space from either side of a string.

Signature: trim(string) string

Examples:

{{ .ip | trim }}
{{ trim "   hello    " }} // output: hello

trimAll

Note: Added in Loki 2.1.

Use this function to remove given characters from the front or back of a string.

Signature: trimAll(chars string,src string) string

Examples:

{{ .path | trimAll "/" }}
{{ trimAll "$" "$5.00" }} // output: 5.00

trimSuffix

Note: Added in Loki 2.1.

Use this function to trim just the suffix from a string.

Signature: trimSuffix(suffix string, src string) string

Examples:

{{  .path | trimSuffix "/" }}
{{ trimSuffix "-" "hello-" }} // output: hello

trimPrefix

Note: Added in Loki 2.1.

Use this function to trim just the prefix from a string.

Signature: trimPrefix(suffix string, src string) string

Examples:

{{  .path | trimPrefix "/" }}
{{ trimPrefix "-" "-hello" }} // output: hello

indent

Note: Added in Loki 2.1.

The indent function indents every line in a given string to the specified indent width. This is useful when aligning multi-line strings.

Signature: indent(spaces int,src string) string

{{ indent 4 .query }}

This indents each line contained in the .query by four (4) spaces.

nindent

Note: Added in Loki 2.1.

The nindent function is the same as the indent function, but prepends a new line to the beginning of the string.

Signature: nindent(spaces int,src string) string

{{ nindent 4 .query }}

This will indent every line of text by 4 space characters and add a new line to the beginning.

repeat

Note: Added in Loki 2.1.

Use this function to repeat a string multiple times.

Signature: repeat(c int,value string) string

{{ repeat 3 "hello" }} // output: hellohellohello

contains

Note: Added in Loki 2.1.

Use this function to test to see if one string is contained inside of another.

Signature: contains(s string, src string) bool

Examples:

{{ if .err contains "ErrTimeout" }} timeout {{end}}
{{ if contains "he" "hello" }} yes {{end}}

hasPrefix and hasSuffix

Note: Added in Loki 2.1.

The hasPrefix and hasSuffix functions test whether a string has a given prefix or suffix.

Signatures:

• hasPrefix(prefix string, src string) bool
• hasSuffix(suffix string, src string) bool

Examples:

{{ if .err hasSuffix "Timeout" }} timeout {{end}}
{{ if hasPrefix "he" "hello" }} yes {{end}}