tail

A cross-platform tail clone written in Rust.

tail is a command-line utility that outputs the last N lines (default 10) or bytes from standard input or one or more files. It supports all standard GNU tail features including follow mode for monitoring file growth, multiple file support with headers, and offset-from-start syntax.

Features

• Line-based output (-n): Output the last N lines (default 10)
• Byte-based output (-c): Output the last N bytes
• Offset from start (+N): Output starting from line/byte N with -n +N or -c +N
• Follow mode (-f/-F): Monitor files for appended data in real time
• Multiple files: Process multiple files with automatic headers
• Header control (-q/-v): Suppress or force file name headers
• Size suffixes: Support for K, M, G, kB, MB, GB, etc.
• Zero-terminated (-z): Use NUL as line delimiter instead of newline
• Process monitoring (--pid): Terminate follow mode when a process dies
• Log rotation (-F/--retry): Handle log file rotation gracefully
• Cross-platform: Works on Linux, macOS, and Windows

Usage Examples

# Display last 10 lines of a file (default)
tail /etc/passwd

# Display last 20 lines from stdin
cat /path/to/file | tail -n 20

# Display last 5 lines of a file
tail -n 5 /etc/passwd

# Display last 100 bytes
tail -c 100 myfile.txt

# Display starting from line 5 (skip first 4 lines)
tail -n +5 myfile.txt

# Display starting from byte 100
tail -c +100 myfile.txt

# Follow a file for new data (like log monitoring)
tail -f /var/log/syslog

# Follow with log rotation support
tail -F /var/log/syslog

# Multiple files with headers
tail -n 5 file1.txt file2.txt file3.txt

# Use size suffixes
tail -c 2K myfile.txt    # Last 2 KiB (2048 bytes)
tail -c 1M myfile.txt    # Last 1 MiB (1048576 bytes)

# Suppress headers with multiple files
tail -q -n 5 file1.txt file2.txt

# Use NUL-terminated lines
tail -z -n 5 myfile.txt

Full Usage

Print the last 10 lines of each FILE to standard output.
With more than one FILE, precede each with a header giving the file name.

With no FILE, or when FILE is -, read standard input.

Usage: tail [OPTIONS] [FILE]...

Arguments:
  [FILE]...  Files to read from (optional, reads stdin if omitted or -)

Options:
  -n, --lines <NUM>         Output the last NUM lines; or use -n +NUM to skip NUM-1 lines at the start
  -c, --bytes <NUM>         Output the last NUM bytes; or use -c +NUM to output starting with byte NUM
  -f, --follow [<MODE>]     Output appended data as the file grows
  -F                        Same as --follow=name --retry
      --retry               Keep trying to open a file if it is inaccessible
  -s, --sleep-interval <N>  With -f, sleep for approximately N seconds between iterations [default: 1]
      --pid <PID>           With -f, terminate after process ID PID dies
  -q, --quiet               Never output headers giving file names
  -v, --verbose             Always output headers giving file names
  -z, --zero-terminated     Line delimiter is NUL, not newline
  -h, --help                Print help
  -V, --version             Print version

Size Suffixes

NUM may have a multiplier suffix:

• b = 512
• kB = 1000, K / KiB = 1024
• MB = 1,000,000, M / MiB = 1,048,576
• GB = 1,000,000,000, G / GiB = 1,073,741,824
• TB = 1,000,000,000,000, T / TiB = 1,099,511,627,776

Building

# Build release binary
cargo build --release

# Run tests
cargo test

# Run linter
cargo clippy

# Format code
cargo fmt

See Also

• iwatakeshi/head — a cross-platform head clone written in Rust, the companion to this project.

License

Apache License 2.0