05 Jan 2012 @ 8:00 PM 

Hello all,

The last post before a long week-end (I will not be able to post tomorrow, and on Monday and Tuesday. I’ll see you on wednesday.

Today, the topic is “The difference between find -exec and find | xargs”

The situation

You have to look into a specific directory and subdirectories for all the files named “*log” because you are quite sure one of them contains the word “error”.

You have two ways to do this :

1 – using -exec

This is a parameter to the find commands that allows you to do an extra command on the found files. The syntax is as follow :

-exec <command> {} \;

<command> replaces your command

{} will be replaced by the name of the found file.

\; terminates the command

i.e. you type :

find . -name \*log -exec grep -i error {} \;

and it will return all the lines containing error, regardless of the case.

2 – using xargs.

xargs is a command that allows the piped data to be passed as parameter to another command. The syntax is as follow :

| xargs <command>

xargs simply puts at the end of the command the piped data. i.e. you type :

find . -name \*log | xargs grep -i

3 – Using a while loop.

Yes, you can do like that, but it is not the topic of this discussion.

 

The difference

What is the main difference between the two?

-exec is going to take each file, and execute the command with it. Using this, you will get a list of all the lines, but not the name of the file, as grep assumes you know which file he talks about, as you have passed the name as parameter !

A sub process will be spawn for each file to be checked.

xargs, on the other end, is going to pass the complete list of files to grep. The name of the files will be shown in the result list.

The separator for the parameters will be the space, and this is OK as long as there is no space in the names of the files (but who puts spaces in the names of the files ? Ah, ok, users…).

In fact, the fail proof  way to deal with this specific request is to make the while loop.

 

The conclusion

Both ways can be useful, depending of the request and the situation. It is important that you understand the different ways those tools work, so that you can choose which one is the best for your usage.

Thank you for reading, and see you next wednesday ! (told you, long week-end for me 🙂 )

 

Posted By: Dimi
Last Edit: 02 Jan 2012 @ 05:17 PM

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Categories: Bash, basics, Snippets


 

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