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// Copyright 2024 Bjørn Erik Pedersen
// SPDX-License-Identifier: MIT
package envhelpers
import (
"regexp"
"strings"
)
var (
varUnquouteRe = regexp.MustCompile(`[\"']\$\{(\w+)@U\}[\"']`)
varRe = regexp.MustCompile(`\$\{(\w+)\}`)
)
// Expand replaces ${var} (and only that) in the string based on the mapping function.
// This signature is identical to the one in the Go standard library,
// but has a more restrictive scope with less ambiguity.
// The value inside ${} must match \w+ (see regexp.MatchString).
//
// A special form of environment variable syntax is supported to allow for removing surrounding
// quoutes (both single and double), useful to setting numeric values in TOML/JSON config files etc.
// Use the "@U" suffix to signal unquoting, e.g. `"${myvar@U}"` or `'${myvar@U}'`. Note that when using the "@U" suffix,
// the variable expression needs to be surrounded by quoutes.
func Expand(s string, mapping func(string) string) string {
if !strings.Contains(s, "${") {
return s
}
firstPass := varUnquouteRe.ReplaceAllStringFunc(s, func(match string) string {
// Remove quoutes and "@U" suffix before passing to mapping function.
return mapping(match[3 : len(match)-4])
})
return varRe.ReplaceAllStringFunc(firstPass, func(varName string) string {
return mapping(varName[2 : len(varName)-1])
})
}
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