an awk program is a series of pattern { actions } statements;
ie if the input line matchs pattern then the actions are performed.
/abc/ { print }
would only print lines that contained the string ''abc''.
Lines are split into fields separated by whitespace - $1 is the first field; $2 the second ...
and $0 is the whole line. Comments can follow the # symbol.
# print those lines where "awk" appears in the first field. $1 ~ /awk/ { print $0; }
An omited pattern matchs every line and an omitted action just prints the line.
The special pattern ''END'' is done after all data is read; so to print the sum of the first column:
{ sum = sum + $1 } END { print sum }
To also find the maximum value of field $1:
{ sum = sum + $1 } $1 > max { max = $1 } END{ print "sum = " sum; print "max value = " max; }
For terse concise summary see:
http://www.cs.princeton.edu/courses/archive/spring12/cos333/awk.help
most Extensive list: AwkChannelWiki: Index of all pages