CODEWITHSUNDEEP
linuxbashshellgrep
Andy
Andy

Reputation: 407

search file content in last n lines of shell script


I use the command the grep file content, and do something.
However, the file size is growing continuous every second. (will larger than 500MB)
Due to the performance issue, I want to grep file content in last N lines rather than entire file content.

if grep -q "SOMETHING" "/home/andy/log/1.log"; then
    ps -ef | grep "127.0.0.1:50000" | awk '{print $2}' | xargs kill; cat /dev/null > /home/andy/log/1.log
fi

How can I modify the script to grep file content in last N lines?
Thanks!

Upvotes: 7

Views: 19937

Answers (2)

glenn jackman
glenn jackman

Reputation: 246774

Another approach is to compare the file size now versus the past and use tail -c to get the difference in characters (bytes)

# prev_size is known
curr_size=$(stat -c %s file.log)
if tail -c $((curr_size - prev_size)) | grep -q pattern; then ...
    # ...
fi
prev_size=$curr_size
# loop

This way you're more certain that you're not missing anything, or grepping too much.

Upvotes: 2

John C
John C

Reputation: 4396

you can use tail -n to get the last n lines of a file.

So you if you wanted to look only at the last 100 lines you could make your script work like this:

if tail -n 100 "/home/andy/log/1.log" | grep -q "SOMETHING"; then
...

Upvotes: 18

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