cols

Smart adaptive formatting of columnar data for Rust.

cols is designed for CLI tools that need terminal-aware table output with tree rendering, multiple output formats, and built-in filtering. Think lsblk, lsmem, or pstree.

Documentation | API Reference | Crates.io

Quick start

[dependencies]
cols = "0.2"

use cols::{Table, Column, print_table_to_string};

let mut table = Table::new();
table.add_column(Column::new("NAME").width_fixed(10));
table.add_column(Column::new("SIZE").width_fixed(6).right(true));

let l1 = table.new_line(None);
table.line_mut(l1).data_set(0, "sda").data_set(1, "100G");

let l2 = table.new_line(None);
table.line_mut(l2).data_set(0, "sdb").data_set(1, "50G");

let output = print_table_to_string(&table).unwrap();

NAME         SIZE
sda          100G
sdb           50G

Tree rendering

use cols::{Table, Column, print_table_to_string};

let mut table = Table::new();
table.add_column(Column::new("NAME").tree(true));
table.add_column(Column::new("SIZE").right(true));

let root = table.new_line(None);
table.line_mut(root).data_set(0, "root").data_set(1, "100");

let c1 = table.new_line(Some(root));
table.line_mut(c1).data_set(0, "child1").data_set(1, "50");

let gc = table.new_line(Some(c1));
table.line_mut(gc).data_set(0, "grandchild").data_set(1, "20");

let c2 = table.new_line(Some(root));
table.line_mut(c2).data_set(0, "child2").data_set(1, "30");

NAME           SIZE
root            100
├─child1         50
│ └─grandchild   20
└─child2         30

Multiple output modes

The same table can be rendered in seven formats without rebuilding it:

use cols::OutputMode;

table.output_mode_set(OutputMode::Json);

Normal — human-readable with column alignment and padding. Raw — compact, separator-delimited. Export — NAME="value" pairs. ShellVar — like Export with shell-safe column names. JSON — typed JSON array of objects. CSV — RFC 4180 with automatic quoting. Markdown — pipe-delimited with alignment support.

Features

• Adaptive column widths with fixed, fractional, or content-sized hints
• Tree rendering with Unicode or ASCII connectors
• 7 output modes: Normal, Raw, Export, JSON, ShellVar, CSV, Markdown
• Group brackets for M:N member/child relationships
• Filter expressions with boolean logic, comparisons, regex, and integer suffixes (K/M/G/T)
• Sorting with custom comparators
• Column alignment: left, center, right (column default with per-cell override)
• Streaming mode: output rows incrementally without buffering the whole table
• Builder API: Column::new("NAME").width_fixed(10).right(true).truncate(true)

Examples

The examples/ directory contains runnable demos:

cargo run --example ls       # simple file listing
cargo run --example tree     # directory tree
cargo run --example json     # all output modes
cargo run --example filter   # filter expressions
cargo run --example groups   # group bracket rendering
cargo run --example sort     # alphabetic vs numeric sorting
cargo run --example wrap     # column wrapping

License

Licensed under either of Apache License, Version 2.0 or MIT License at your option.