Table of Contents

The head command prints the beginning of files or input streams. It is commonly used to preview data, inspect headers, and limit output in scripts.

Overview

Use head when you need to:

  • Preview the first lines of large files
  • Inspect file headers (CSV, logs, configs)
  • Limit pipeline output for quick checks
  • Read the first N bytes of binary/text streams
  • Reduce noisy output during debugging

Syntax

head [options] [file...]

Common forms:

# Default: first 10 lines
head app.log

# First 20 lines
head -n 20 app.log

# First 100 bytes
head -c 100 payload.bin

If no files are provided, head reads from standard input.

Default Behavior

  • Without options, head prints the first 10 lines.
  • With multiple files, file headers are printed before each section.
  • head is read-only and does not modify input files.

Common Options

Option Purpose Example
-n N Show first N lines head -n 30 app.log
-c N Show first N bytes head -c 256 data.bin
-q Never print file name headers head -q file1 file2
-v Always print file name headers head -v file1 file2

GNU head also supports suffixes with -c such as K, M, and G.

Examples

# Preview first 20 lines of a log
head -n 20 app.log

# Show first line (useful for CSV headers)
head -n 1 users.csv

# Show first 500 bytes of a file
head -c 500 archive.dat

# Preview first 3 lines from each of multiple files
head -n 3 server1.log server2.log

# Suppress per-file headers when reading multiple files
head -n 2 -q a.txt b.txt c.txt

# Force per-file headers when reading multiple files
head -n 2 -v a.txt b.txt c.txt

# Limit command output in a pipeline
journalctl -u nginx | head -n 50

# Inspect first few paths from find output
find . -type f | head -n 10

Working with Bytes vs Lines

  • -n is line-oriented and respects line boundaries.
  • -c is byte-oriented and may cut in the middle of a line or multibyte character.

Use -n for human-readable text previews. Use -c for protocol headers, binary checks, or fixed-size reads.

Integration Patterns

Quick log inspection:

head -n 40 /var/log/syslog

Preview generated output from scripts:

./generate-report.sh | head -n 25

Validate sorted output quickly:

sort big-list.txt | head -n 10

Safe Usage Guidelines

  1. Use head before full processing to validate file format and structure.
  2. Combine with -n 1 to safely inspect headers in CSV or TSV files.
  3. Use -q in scripts when predictable output formatting is required.
  4. Prefer -n for text and -c for byte-accurate inspection.

Performance Tips

  1. head is efficient for large files because it stops reading after requested output.
  2. Use head early in pipelines during debugging to reduce processing time.
  3. For bottom-of-file inspection, use tail instead of reading full file then filtering.

Troubleshooting

Output includes ==> file <== headers unexpectedly

Cause: Multiple files were passed, so head shows per-file labels.

Fix:

head -q -n 5 file1 file2

head -c output looks truncated or garbled

Cause: Byte truncation may split multibyte text characters.

Fix:

  • Use -n for text data
  • Keep -c for raw byte inspection use cases

Need first N lines but from piped command

Fix:

some_command | head -n 20

Notes

head and tail are complementary tools for quick top/bottom inspection of data.

For command details and implementation-specific behavior, run:

man head
head --help
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