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How to grep for first entry in a file?

 
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# 1  
Old 10-02-2014
How to grep for first entry in a file?
Hello friends, I have a question.

Sometimes I have to search for an entry in a file that is repeated thousands of times. Can you tell me how to search so that i get limited results?

For example:

Code:
file: myfile.txt

grep "hello world" myfile.txt

this above grep will generate 5000 results, scrolling the screen.

How can I view just the first 10?

Thanks again
# 2  
Old 10-02-2014
If I want the first 10 lines
Code:
 ${command that generates more results than I want} | head -10

And if I want the last 10
Code:
 ${command that generates more results than I want} | tail -10

This User Gave Thanks to Skrynesaver For This Post:
DallasT
# 3  
Old 10-02-2014
Thank you friend
# 4  
Old 10-02-2014
Quote:
Originally Posted by Skrynesaver
Code:
 ${command that generates more results than I want} | head -10

This is of course correct, but - depending on the length of the file/stream to read - might consume considerable more time than necessary.

sed might be a viable alternative because it can be told to stop (even reading) after the first match:

Code:
sed -n '/<regexp to search for>/ {p;q;}' /path/to/file

I hope this helps.

bakunin


/PS: to verify what i have said above i used two small scripts, where one contains the sed-line (mysed.sh) and the other contains the grep-piped-in-head-line, each against the same file. Every line was executed 100 times in a loop. Here are the results, each script has been run times and the time of the third run was measured to alleviate effects of file caching.

Code:
# ./mygrep.sh > /dev/null ; ./mygrep.sh > /dev/null ; time ./mygrep.sh > /dev/null
real    0m0.20s
user    0m0.08s
sys     0m0.08s

# ./mysed.sh > /dev/null ; ./mysed.sh > /dev/null ; time ./mysed.sh > /dev/null   
real    0m0.14s
user    0m0.04s
sys     0m0.04s

Last edited by bakunin; 10-02-2014 at 11:07 AM..
# 5  
Old 10-02-2014
The grep -m option may be of some interest:
Quote:
-m NUM, --max-count=NUM
Stop reading a file after NUM matching lines. If the input is standard input from a regular file, and NUM matching lines are output, grep ensures that the standard input is positioned to just after the last matching line before exiting, regardless of the presence of trailing context lines. This enables a calling process to resume a search. When grep stops after NUM matching lines, it outputs any trailing context lines. When the -c or --count option is also used, grep does not output a count greater than NUM. When the -v or --invert-match option is also used, grep stops after outputting NUM non-matching lines.
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