yq
v4.x
v4.x
  • yq
  • How It Works
  • Recipes
  • Upgrading from V3
  • Commands
    • Evaluate
    • Evaluate All
    • Shell Completion
  • Operators
    • Add
    • Alternative (Default value)
    • Anchor and Alias Operators
    • Array to Map
    • Assign (Update)
    • Boolean Operators
    • Collect into Array
    • Column
    • Comment Operators
    • Compare Operators
    • Contains
    • Create, Collect into Object
    • Date Time
    • Delete
    • Divide
    • Document Index
    • Encode / Decode
    • Entries
    • Env Variable Operators
    • Equals
    • Eval
    • File Operators
    • Filter Operator
    • Flatten
    • Group By
    • Has
    • Keys
    • Kind
    • Length
    • Line
    • Load
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    • Max
    • Modulo
    • Multiply (Merge)
    • Omit
    • Parent
    • Path
    • Pick
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    • Pivot
    • Recursive Descent (Glob)
    • Reduce
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    • Select
    • Shuffle
    • Slice Array
    • Sort
    • Sort Keys
    • Split into Documents
    • String Operators
    • Style
    • Subtract
    • Tag
    • To Number
    • Traverse (Read)
    • Union
    • Unique
    • Variable Operators
    • With
  • Usage
    • Output format
    • Working with CSV, TSV
    • Working with JSON
    • Working with Properties
    • Working with XML
    • Working with LUA
    • Working with TOML
    • Working with Shell Output
    • Front Matter
    • Split into multiple files
    • GitHub Action
    • Tips, Tricks, Troubleshooting
  • Github Page
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  • Dynamically evaluate a path
  • Dynamically update a path from an environment variable

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  1. Operators

Eval

Use eval to dynamically process an expression - for instance from an environment variable.

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".

Tip: This can be a useful way to parameterise complex scripts.

Dynamically evaluate a path

Given a sample.yml file of:

pathExp: .a.b[] | select(.name == "cat")
a:
  b:
    - name: dog
    - name: cat

then

yq 'eval(.pathExp)' sample.yml

will output

name: cat

Dynamically update a path from an environment variable

The env variable can be any valid yq expression.

Given a sample.yml file of:

a:
  b:
    - name: dog
    - name: cat

then

pathEnv=".a.b[0].name"  valueEnv="moo" yq 'eval(strenv(pathEnv)) = strenv(valueEnv)' sample.yml

will output

a:
  b:
    - name: moo
    - name: cat
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Last updated 2 years ago

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