The uniq command removes only the adjacent duplicate lines. Otherwise, the action is not executed, and nothing is printed. ![]() ' your_file > deduplicated_fileįor every line of the file, if the expression succeeds, the line is printed to the output. false if the occurrences are greater than zeroĪwk statements consist of a pattern-expression and an associated action.true if the occurrences are zero/empty string.Summing up, the whole expression evaluates to: Note: The operation is executed after we access the variable's value.If the value is empty, awk converts it to 0 (number) automatically and then it gets increased.The ++ operation increases the variable's value ( visited) by one.If visited returns a number equal to zero or an empty string, this negation is resolved to true.If visited returns a number greater than zero, this negation is resolved to false.By default, variables are initialized to the empty string, which is zero if converted to a number.In awk, any nonzero numeric value or any nonempty string value is true.visited accesses the value stored in the map with a key equal to $0 (the line being processed), a.k.a.The $0 variable holds the contents of the line currently being processed.We don't have to initialize it because awk will do it the first time we access it. visited is a variable of type associative array (a.k.a. ![]() The awk "script" !visited++ is executed for each line of the input file.I did my research, and here is what is going on: I was not familiar with awk, and I wanted to understand how this can be accomplished with such a short script ( awkward). For each line of the file, if the line occurrences are zero, then it increases them by one and prints the line, otherwise, it just increases the occurrences without printing the line. The script keeps an associative array with indices equal to the unique lines of the file and values equal to their occurrences. ![]()
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