Use ack instead of grep to parse text files • Hacker News Board

Re: Use ack instead of grep to parse text files

#31

Post by grabastic » Mon, Dec 24, 2012, 10:00 PM UTC

GlennS wrote: post #16

Is it worth learning grep or ack or a similar tool? When I need to do these sort of tasks, I do them in a scripting language with some combination of split() and regex instead of using command line tools. But, I'm just doing that because it's what I know. Would I end up saving a significant amount of time if I learned to use grep instead?

I'd say start with ack for its ease of use, but knowing grep is important. I prefer ack but most of the boxes i work on don't have ack installed (and won't).

Re: Use ack instead of grep to parse text files

#32

Post by grabastic » Mon, Dec 24, 2012, 10:02 PM UTC

grabastic wrote: post #31

GlennS wrote: post #16

Is it worth learning grep or ack or a similar tool? When I need to do these sort of tasks, I do them in a scripting language with some combination of split() and regex instead of using command line tools. But, I'm just doing that because it's what I know. Would I end up saving a significant amount of time if I learned to use grep instead?

I'd say start with ack for its ease of use, but knowing grep is important. I prefer ack but most of the boxes i work on don't have ack installed (and won't).

Also, these aren't particularly good examples of ack vs grep... as others have pointed out.

Re: Use ack instead of grep to parse text files

#33

Post by philh » Mon, Dec 24, 2012, 10:03 PM UTC

gnosis wrote: post #2

ack '(?=silver).*needle' haystack is really not the same as: grep needle haystack|grep silver Because with the double grep method, a match will be made whether "silver" is before or after "needle"; while with the single ack command shown above, a match will only be made when "silver" comes before "needle". Also, I'm not sure why the author uses ack '(?=silver).*needle' haystack instead of simply: ack 'silver.*needle'…

ack hilights results by default, so `(?=silver.*)needle` would potentially be useful. But, yes, not the same as the grep|grep.

Re: Use ack instead of grep to parse text files

#34

Post by anonymoushn » Mon, Dec 24, 2012, 10:08 PM UTC

carbocation wrote: post #8

Why is: ack -C5 'scope(?!.*lambda)' app/models Better than: grep -C5 scope app/models | grep -v lambda ?

The first one gets you five lines around all of the scopes without lambdas. The second one gets you five lines around all the scopes (including those with lambdas) and then omits all of the lines with lambdas, some of which will have caused a match in the first grep, and some of which may be part of the context of matches in the first grep. You will get both contexts with no match in the middle and matches with incomplete contexts.

Re: Use ack instead of grep to parse text files

#35

Post by halayli » Mon, Dec 24, 2012, 10:11 PM UTC

grep -E is good enough. But whatever works.

Saying "You should stop using them. Now." is ridiculous. Why do I need to stop anything if it does what I need?

Re: Use ack instead of grep to parse text files

#36

Post by eliben » Mon, Dec 24, 2012, 10:13 PM UTC

ack is a great tool for searching within text files, not for parsing them.

[shameless plug] Try also the pure-Python based alternative to ack called "pss" (pip/easy_install or https://bitbucket.org/eliben/pss).

Re: Use ack instead of grep to parse text files

#37

Post by mistermcgruff » Mon, Dec 24, 2012, 10:14 PM UTC

No.

Re: Use ack instead of grep to parse text files

#38

Post by carbocation » Mon, Dec 24, 2012, 10:22 PM UTC

anonymoushn wrote: post #34

carbocation wrote: post #8

Why is: ack -C5 'scope(?!.*lambda)' app/models Better than: grep -C5 scope app/models | grep -v lambda ?

The first one gets you five lines around all of the scopes without lambdas. The second one gets you five lines around all the scopes (including those with lambdas) and then omits all of the lines with lambdas, some of which will have caused a match in the first grep, and some of which may be part of the context of matches in the first grep. You will get both contexts with no match in the middle and matches with incom…

Quite right. The downfalls of posting untested code...

Re: Use ack instead of grep to parse text files

#39

Post by jjoe » Mon, Dec 24, 2012, 10:22 PM UTC

Is anyone else turned off by the tone of the blog post and the attitude of the poster? There's gotta be a better way to showcase the usefulness of a tool.

Re: Use ack instead of grep to parse text files

#40

Post by Firehed » Mon, Dec 24, 2012, 10:23 PM UTC

nene wrote: post #5

gnosis wrote: post #2

ack '(?=silver).*needle' haystack is really not the same as: grep needle haystack|grep silver Because with the double grep method, a match will be made whether "silver" is before or after "needle"; while with the single ack command shown above, a match will only be made when "silver" comes before "needle". Also, I'm not sure why the author uses ack '(?=silver).*needle' haystack instead of simply: ack 'silver.*needle'…

Maybe it's because you can write the latter also with plain grep: grep 'silver.*needle' haystack

That assumes that "silver" will appear before "needle", which may not always be the case. `grep needle file | grep silver` gets you lines containing both "silver" and "needle" but not necessarily in that order.