[j_z_reeves]

nice, I finally took the time to read the man pages for awk. And whipped out a script to count the number of errors occurred for a particular day for a postgres log file.

   cat logfile | awk '/ERROR:/ {counts[$1] = counts[$1] + 1}; END { for (day in counts) print day " : " counts[day]}' | sort

I just needed to know how awk programs are structured, the rest is just simple programming!

EDIT: I'm not sure if it's actually correct however...

[tejtm]

j_z_reeves 9 hours ago [-]

> cat logfile | awk '/ERROR:/ {counts[$1] = counts[$1] + 1}; END { for (day in counts) print day " : " counts[day]}' | sort

Great first program! a bit less verbose could be

> awk '/ERROR:/ {counts[$1]++}END{...}' logfile

there are also ways of sorting the output but within (g)awk (asort & asorti) but sorting externally as you have is more flexible and engages another core which can be faster on large input

[j0057]

Without knowing the format of logfile, that still seems obviously correct to me.

[j_z_reeves]

I was surprised by the counts[$1] = counts[$1] + 1, since I didn't think it would correctly coerce a non-existing value to a 0.

[xorcist]

Apart from the useless use of cat, since sort does the work here something like the following would probably suffice:

grep ERROR logfile | cut -f 1 -d ' ' | sort | uniq -c

[j0057]

There's really nothing useless about that use of cat: it makes the pipeline compose better from left to right. It's not like you have to pay 25 cents for each process you spawn.

[xorcist]

So does the pipeline above.

It's not detrimental to performance since an empty cat is a no-op in a pipeline. You can have any number of them. But commands should be written for humans to understand, and inserting no-ops is a distraction to the reader.

In the trivial example, "grep needle haystack" reads better than "cat haystack | grep needle".

[j_z_reeves]

yes that would also work! I forgot about the `-c` argument for uniq.