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39 lines
947 B
Markdown
39 lines
947 B
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, be it a path `.a.b.c | select(. == "cat")`, or an update `.a.b.c = "gogo"`.
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Tip: This can be a useful way to parameterise complex scripts.
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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")', a: {b: [{name: dog}, {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: {b: [{name: dog}, {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: {b: [{name: moo}, {name: cat}]}}
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```
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