mirror of https://github.com/mikefarah/yq.git
55 lines
1.1 KiB
Markdown
55 lines
1.1 KiB
Markdown
# Eval
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Use `eval` to dynamically process an expression - for instance from an environment variable.
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`eval` takes a single argument, and evaluates that as a `yq` expression. Any valid expression can be used, beit a path `.a.b.c | select(. == "cat")`, or an update `.a.b.c = "gogo"`.
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Tip: This can be useful way parameterise complex scripts.
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{% hint style="warning" %}
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Note that versions prior to 4.18 require the 'eval/e' command to be specified. 
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`yq e <exp> <file>`
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{% endhint %}
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## Dynamically evaluate a path
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Given a sample.yml file of:
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```yaml
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pathExp: .a.b[] | select(.name == "cat")
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a:
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b:
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- name: dog
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- name: cat
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```
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then
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```bash
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yq 'eval(.pathExp)' sample.yml
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```
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will output
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```yaml
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name: cat
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```
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## Dynamically update a path from an environment variable
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The env variable can be any valid yq expression.
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Given a sample.yml file of:
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```yaml
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a:
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b:
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- name: dog
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- name: cat
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```
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then
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```bash
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pathEnv=".a.b[0].name" valueEnv="moo" yq 'eval(strenv(pathEnv)) = strenv(valueEnv)' sample.yml
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```
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will output
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```yaml
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a:
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b:
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- name: moo
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- name: cat
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```
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