Master Fast Log Error Detection with Tail, Grep, and Sed Commands

Quickly Locate Errors in Large Log Files

Use dynamic log viewing commands to inspect log files efficiently. tail -f catalina.out Open a log file from the beginning: cat catalina.out Redirect a portion of the log to a new file for focused analysis:

# cat -n catalina.out | grep 717892466 > nanjiangtest.txt

Simple Tail/Head Command Usage

# tail -n number catalina.out        # Show the last <em>number</em> lines
# tail -n +number catalina.out       # Show all lines after <em>number</em>
# head -n number catalina.out        # Show the first <em>number</em> lines
# head -n -number catalina.out       # Show all lines except the last <em>number</em>

Method 1 – Find Line Numbers by Keyword

After obtaining a few matching lines with grep, retrieve surrounding context using the line numbers:

# cat -n catalina.out | grep "keyword"
# cat -n catalina.out | grep "keyword" | tail -n +13230539 | head -n 10

"tail -n +13230539" queries logs after line 13230539.

"head -n 10" limits the result to the first 10 records.

Method 2 – Search Within a Specific Time Range

First verify that the desired time range exists in the current log file, then use grep or sed to extract it:

grep '11:07 18:29:20' catalina.out
grep '11:07 18:31:11' catalina.out

sed -n '/11:07 18:29:20/,/11:07 18:31:11/p' catalina.out
sed -n '/11:07 18:29:/,/11:07 18:31:/p' catalina.out

Method 3 – Count Occurrences of a Specific String

# grep '1175109632' catalina.out | wc -l
154

Method 4 – Search the Last N Lines for a Keyword

# tail -n 20 catalina.out | grep 'INFO Takes:1'

Method 5 – Highlight Keyword Results

# tail -n 20 catalina.out | grep 'INFO Takes:1' --color

Method 6 – Highlight with Context Lines

# tail -n 20 catalina.out | grep 'INFO Takes:1' --color -A2

Method 7 – Paginated View Using more/less

# tail -n 2000 catalina.out | grep 'INFO Takes:1' --color -A2 | more
# tail -n 2000 catalina.out | grep 'INFO Takes:1' --color -A2 | less

Additional Navigation Shortcuts (less)

Full‑screen navigation: Ctrl+F forward one screen, Ctrl+B back one screen, Ctrl+D forward half screen, Ctrl+U back half screen.

Line navigation: j forward one line, k back one line.

Other commands: G go to last line, g go to first line, q or ZZ quit.