Field names first
Say Where("status", "active"), not "find column 4 and remember the header."
CSV transforms for Go CLIs
Turn messy CSVs into useful tools.
simplecsv gives small command-line programs a clear path from raw rows to filtered, reshaped, joined, and summarized output. No database. No query language. Just Go.
$ go run . people.csv
// read once
people, _ := simplecsv.ReadCsvFileE(path)
// field-first transforms
active, _ := people.Where("status", "active")
summary, _ := active.GroupBy(...)
// write a useful result
summary.WriteCsvFileE("report.csv")
ok 3,842 rows -> 17 groups
01
Read
files or streams
02
Transform
fields and rows
03
Segment
filter and sort
04
Combine
join and concat
05
Report
group and write
Why simplecsv
Small surface. Serious invariants.
CSV scripts tend to start small. simplecsv keeps them small while taking care of the row-index mistakes and schema surprises that make them brittle.
Never mutate by accident
Transform methods return independent CSVs. Build a pipeline without hidden changes to earlier values.
All cells stay strings
Keep storage predictable. Parse numbers only where a filter, sort, or aggregate actually needs them.
More than read and write
Join files, deduplicate rows, reshape columns, group values, and build reports without pulling in a database.
Predictable failures
Unique headers and uniform row widths are enforced. Use *E variants when a useful error matters.
Ready for real exports
Read delimiters and streams, handle BOMs, limit untrusted input, and sanitize spreadsheet-bound output.
A useful first program
Readable enough to hand to your future self.
Most tools need the same sequence: load, keep the rows that matter, choose the output shape, and write it somewhere useful.
ReadCsvFileE
Where
FilterByField
OnlyThisFields
package main
import (
"log"
"strconv"
"github.com/osvik/simplecsv"
)
func main() {
people, err := simplecsv.ReadCsvFileE("people.csv")
if err != nil {
log.Fatal(err)
}
active, ok := people.Where("status", "active")
if !ok {
log.Fatal("status field not found")
}
adults, ok := active.FilterByField("age", func(value string) bool {
age, err := strconv.Atoi(value)
return err == nil && age >= 18
})
if !ok {
log.Fatal("age field not found")
}
result, ok := adults.OnlyThisFields([]string{"id", "name", "age"})
if !ok {
log.Fatal("could not select output fields")
}
if err := result.WriteCsvFileE("active-adults.csv"); err != nil {
log.Fatal(err)
}
}