arrays in awk
awk is even better than i thought it is. It has arrays. Recently i needed to examine a log file, which includes mixed output from several threads, and to find 2 latest strings of each thread. I didn’t know how to do it, till a coworker mentioned to me about those arrays.
The script is extremely simple:
cat my_log_file.txt | awk '{arr[$2, 1] = arr[$2, 0]; arr[$2, 0]=$0} END { for (s in arr) print s" : "arr[s] }'
Some explanations:
{arr[$2, 1] = arr[$2, 0]; arr[$2, 0]=$0}- an operation which is performed on every line. Column 2 is the thread number. I keep in array with index [threadNumber,0] the last line and the line before last in index [threadNumber,1]END { for (s in arr) print s" : "arr[s] }'
- the final operation - print all the array with it indexes
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