Action and pattern structure of AWK

AWK programs are sequences of one or more patterns followed by action statements. These action-pattern statements are separated by newlines. Both actions (AWK commands) and patterns (search patterns) are optional, hence we use { } to distinguish them:

/ search pattern / { action / awk-commands }/ search pattern / { action / awk-commands }

AWK reads each input line one after the other, and searches for matches of the given pattern. If the current input line matches the given pattern, a corresponding action is taken. Then, the next input line is read and the matching of patterns starts again. This process continues until all input is read.

In AWK syntax, we can omit either patterns or actions (but not both) in a single pattern-action statement. Where a search pattern has no action statement (AWK command), each line for which a pattern matches is printed to the output.