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The less command is an interactive pager for viewing text one screen at a time. It is ideal for reading large files, log output, and command pipelines without loading content into an editor.

Overview

Use less when you need to:

  • View large files without opening an editor
  • Scroll through logs and command output interactively
  • Search for patterns inside a file
  • Follow growing files (similar to live log tailing)
  • Navigate quickly by lines, percentages, and matches

Syntax

less [options] [file...]

Common forms:

# View a file
less /var/log/syslog

# View command output
journalctl -u nginx | less

# Open at first match
less +/ERROR app.log

# Follow mode (live updates)
less +F app.log

If no file is supplied, less reads from standard input.

Common Options

Option Purpose Example
-N Show line numbers less -N app.log
-S Chop long lines (no wrap) less -S data.tsv
-R Display raw ANSI color escapes less -R build.log
-X Do not clear screen on exit less -X notes.txt
-F Quit if content fits one screen less -F README.md
-i Case-insensitive search unless uppercase in pattern less -i app.log
-I Always case-insensitive search less -I app.log
+N Start at line N less +120 app.log
+/PATTERN Start at first PATTERN match less +/timeout app.log

Essential Navigation Keys

Key Action
Space Next page
b Previous page
Enter Next line
k / y Previous line
g Go to first line
G Go to last line
N g Go to line N (example: 250g)
N% Go to percentage in file (example: 50%)
q Quit

Search and Match Navigation

  • /pattern search forward
  • ?pattern search backward
  • n jump to next match
  • N jump to previous match

Examples while inside less:

  • /ERROR
  • /connection timeout
  • ?Exception

Following Live Output

Use follow mode to watch files that are growing:

less +F /var/log/syslog

In follow mode:

  • Press Ctrl+C to pause following and return to normal navigation
  • Press F to resume following

This is similar to tail -f but allows full interactive navigation when paused.

Examples

# Browse a large log with line numbers
less -N /var/log/nginx/access.log

# Preserve color output from grep
grep --color=always -n "ERROR" app.log | less -R

# View wide output without wrapping
ps aux | less -S

# Open directly at end of file
less +G app.log

# Open multiple files and move between them (:n and :p inside less)
less app.log app.log.1 app.log.2

# View compressed logs using zless wrapper
zless app.log.gz

Useful In-Session Commands

  • h open built-in help
  • :n go to next file in argument list
  • :p go to previous file in argument list
  • = show current file position

Safe Usage Guidelines

  1. Use less instead of cat for large files to avoid terminal flooding.
  2. Use -R when paging colorized output from other tools.
  3. Use -S for wide tabular output to prevent wrapped, hard-to-read lines.
  4. Prefer less +/pattern for quicker incident triage in large logs.

Performance Tips

  1. less streams data and is efficient for very large files.
  2. Piping into less keeps interactive control while avoiding huge terminal output.
  3. Disable line wrapping (-S) for large structured rows to improve readability.

Troubleshooting

Colors disappear when piping output into less

Cause: Color escapes are stripped or not rendered.

Fix:

grep --color=always "error" app.log | less -R

Long lines wrap and become hard to read

Cause: Default line wrapping.

Fix:

less -S wide-output.txt

File keeps updating and view jumps

Cause: Follow mode enabled.

Fix:

  • Press Ctrl+C to pause follow mode
  • Use normal navigation commands, then press F to resume

Notes

less is often configured as the default pager through the PAGER environment variable.

For command details and implementation-specific behavior, run:

man less
less --help
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