expr

Evaluates the expr language for each row.

Behavior:

• Parses and evaluates an expression against each row of input data.
• Default mode outputs only the expression result (original row data is not included).
• Supports arithmetic, string, logical operations, function calls, and lambda expressions.
• See tva --help-expr for a quick reference to the expr language and the detailed CLI instructions.

Input:

• Reads from files or standard input.
• Files ending in .gz are transparently decompressed.
• Use stdin to explicitly read from stdin, this is different behavior from other commands.
• Use -r for inline row data without file input.

Output:

• Default: outputs the evaluated result for each row.
• Use -m flag to change output mode: eval (default), add, mutate, skip-null, filter.

Header behavior:

• Supports basic header mode. See tva --help-headers for details.
• When headers are enabled, column names can be referenced with @name syntax.
• The output header is determined by the expression:
  • as @name binding: uses name as the header
  • @column_name reference: uses column_name as the header
  • @1 with input headers: uses the first input column name
  • Other expressions: uses the formatted last expression string

Examples:

1. Simple arithmetic tva expr -E '2 + 3 * 4'

2. Calculate total from price and quantity tva expr -H -E '@price * @qty' data.tsv

3. Named output column with as tva expr -H -E '@price * @qty as @total' data.tsv

4. Chain functions with pipe tva expr -H -E '@name | trim() | upper()' data.tsv

5. Conditional expression tva expr -H -E 'if(@score >= 70, "pass", "fail")' data.tsv

6. Add new column(s) to original row tva expr -H -m extend -E '@price * @qty as @total' data.tsv

7. Mutate (modify) existing column value tva expr -H -m mutate -E '@age + 1 as @age' data.tsv

8. Filter rows by condition tva expr -H -m filter -E '@age > 25' data.tsv

9. Skip null results tva expr -H -m skip-null -E 'if(@score >= 70, @name, null)' data.tsv

10. Test with inline row data tva expr -n 'price,qty' -r '100,2' -E '@price * @qty'