Rocky Linux Core Commands: Page 3

This page explores commands for viewing large files and searching for patterns within file content.

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11. less - Paged File Viewer (Forward and Backward)

Purpose: The less command is a powerful file viewer that allows you to view file contents one page at a time. Unlike more, it allows both forward and backward navigation, making it ideal for large files.

Syntax: less [OPTIONS] FILE...

Key Navigation:

• Spacebar or f: Scroll forward one page.
• b: Scroll backward one page.
• Arrow keys (Up/Down): Scroll line by line.
• /pattern: Search forward for a pattern.
• ?pattern: Search backward for a pattern.
• n: Go to the next match (after searching).
• N: Go to the previous match (after searching).
• q: Quit less.

Examples:

less /var/log/syslog
less large_config.txt

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12. more - Paged File Viewer (Forward Only)

Purpose: The more command is another file viewer that displays content one screen at a time. It's simpler than less, primarily allowing forward movement through the file.

Syntax: more [OPTIONS] FILE...

Key Navigation:

• Spacebar: Scroll forward one page.
• Enter: Scroll forward one line.
• q: Quit more.

Examples:

more /etc/services
more long_readme.md

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13. head - Display the Beginning of a File

Purpose: The head command displays the first few lines of a file. By default, it shows the first 10 lines.

Syntax: head [OPTIONS] FILE...

Key Options:

• -n NUM: Displays the first NUM lines.

Examples:

head my_log.txt
head -n 5 configuration.ini

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14. tail - Display the End of a File

Purpose: The tail command displays the last few lines of a file. By default, it shows the last 10 lines. It's often used for monitoring log files.

Syntax: tail [OPTIONS] FILE...

Key Options:

• -n NUM: Displays the last NUM lines.
• -f: (follow) Outputs appended data as the file grows. Excellent for real-time log monitoring.

Examples:

tail access.log
tail -n 20 error.log
tail -f /var/log/messages

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15. grep - Search for Patterns in Files

Purpose: The grep command (Global Regular Expression Print) searches for lines matching a specified pattern in one or more files.

Syntax: grep [OPTIONS] PATTERN [FILE...]

Key Options:

• -i: (ignore case) Performs a case-insensitive search.
• -v: (invert match) Displays lines that DO NOT match the pattern.
• -r or -R: (recursive) Searches directories recursively.
• -n: (line number) Displays the line number along with the matching line.
• -c: (count) Displays only a count of matching lines.

Examples:

grep "error" /var/log/syslog
grep -i "warning" myapp.log
grep -r "TODO" ~/projects/
grep -n "function main" program.c