英文:
Is there a simple way to grab the first line from a file with helm?
问题
我正在尝试使用Helm创建一个Kubernetes ConfigMap，它只包含配置文件中的第一行内容。我将文件放在helm/config/file.txt中，其中包含多行内容，但我只想提取第一行。我首次尝试的方法是循环遍历文件的每一行，但在第一次循环后退出：
apiVersion: v1
kind: ConfigMap
metadata:
name: one-line-cm
data:
first-line:
{{- range .Files.Lines "config/file.txt" }}
{{ . }}
{{ break }} # 这不是真实的语法
{{- end }}
不幸的是，break在Helm中似乎不是一个概念/函数，尽管它在Golang中是存在的。我通过艰难的方式发现了这一点，并在这篇文章中阅读到了一个类似的问题：https://stackoverflow.com/questions/60966946/helm-break-loop-range-in-template
我并不固执于使用循环，我只是想知道是否有其他解决方案来执行使用Helm语法从文件中提取第一行的简单任务。
英文:
I am attempting to create a kubernetes ConfigMap with helm, which simply consists of the first line within a config file. I put my file in helm/config/file.txt, which has several lines of content, but I only want to extract the first. My first attempt at this was to loop over the lines of the file (naturally), but quit out after the first loop:
apiVersion: v1
kind: ConfigMap
metadata:
name: one-line-cm
data:
first-line:
{{- range .Files.Lines "config/file.txt" }}
{{ . }}
{{ break }} # not a real thing
{{- end }}
Unfortunately, break doesn't seem to be a concept/function in helm, even though it is within golang. I discovered this the hard way, as well as reading about a similar question in this other post: https://stackoverflow.com/questions/60966946/helm-break-loop-range-in-template
I'm not stuck on using a loop, I'm just wondering if there's another solution to perform the simple task of extracting the first line from a file with helm syntax.
答案1
得分: 1
我已经确定以下是最简洁的解决方案：
.Files.Lines "config/file.txt" | first
（顺便提一下，由于我的文件内容包含特殊字符，我在实际解决方案中必须使用squote进行管道处理）
在浏览Helm的文档以寻找替代函数后，我找到了一个可行的解决方案，只是不太美观：
apiVersion: v1
kind: ConfigMap
metadata:
name: one-line-cm
data:
first-line: |
{{ index (regexSplit "\n" (.Files.Get "config/file.txt") -1) 0 }}
上面的代码实现了以下功能（从内到外）：
.Files.Get "config/file.txt"返回文件内容的字符串表示。regexSplit "\n" <step-1> -1将步骤1中的文件内容按换行符分割（-1 表示返回尽可能多的子字符串匹配）。index <step-2> 0从步骤2返回的列表中获取第一项（索引为0）。
希望这能帮助到其他遇到类似情况的人，我仍然欢迎其他解决方案的建议。
英文:
EDIT:
I've determined the following is the cleanest solution:
.Files.Lines "config/file.txt" | first
(As a side note, I had to pipe to squote in my acutal solution due to my file contents containing special characters)
After poking around in the helm docs for alternative functions, I came up with a solution that works, it's just not that pretty:
apiVersion: v1
kind: ConfigMap
metadata:
name: one-line-cm
data:
first-line: |
{{ index (regexSplit "\\n" (.Files.Get "config/file.txt") -1) 0 }}
This is what's happening above (working inside outward):
.Files.Get "config/file.txt"is returning a string representation of the file contents.regexSplit "\\n" <step-1> -1is splitting the file contents from step-1 by newline (-1 means return the max number of substring matches possible)index <step-2> 0is grabbing the first item (index 0) from the list returned by step-2.
Hope this is able to help others in similar situations, and I am still open to alternative solution suggestions.
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