Awk a file line by line

Awk's default program action is to print the entire line, which is what 'print' does when invoked without parameters. This means that these three examples are the same:.

This is redundant, but it does have the virtue of making the action more obvious. There's a subtle issue involved here, however. In most computer languages, strings are strings, and numbers are numbers.

There are operations that are unique to each, and one must be specifically converted to the other with conversion functions. You don't concatenate numbers, and you don't perform arithmetic operations on strings. Awk, on the other hand, makes no strong distinction between strings and numbers. In computer-science terms, it isn't a 'strongly-typed' language.

All data in Awk are regarded as strings, but if that string also happens to represent a number, numeric operations can be performed on it. So we can perform an arithmetic comparison on the date field. The first new item in this example is the END statement. To explain this, I have to extend the general form of an Awk program.

The subsequent body of the Awk program consists of a series of search patterns, each with its own program action. Awk scans each line of the input file for each search pattern, and performs the appropriate actions for each string found. Once the file has been scanned, an END clause can be used to perform any final actions required. So, this example doesn't perform any processing on the input lines themselves. All it does is scan through the file and perform a final action: print the number of lines in the file, which is given by the NR variable.

NR stands for 'number of records'. NR is one of Awk's 'pre-defined' variables. There are others, for example the variable NF gives the number of fields in a line, but a detailed explanation will have to wait for later.

I invoke Awk as follows:. The following command will print only the lines from my sample file who have characters more than This is the way you can use it:. In this example, I will be using the redirection operator with my awk command to print only the names of the employees column 1 to a new file:.

Awk has some built-in commands that you can use to filter the output. For example, the NF command is used to keep a count of the fields within the current input record. Here, we will use the NF command to print only the non-empty lines of the file:. Another built-in function called NR keeps a count of the number of input records usually lines of a given file. You can use this function in awk as following to count the number of lines in a file:.

This was the basic information you need to start with splitting files with the awk command. You can use the combination of these examples to fetch more meaningful information from your file of strings through awk. The NR variable indicates the number of records in a file. The value of NR is 1 for the first line. The following command will print lines for which the NR value is greater than 1. The following output will be produced after running the above commands. The output includes all lines other than the first line of the file.

The output shows all lines other than the first line of the file. Here, the if statement will be true only when the NR value does not equal 1. The output includes all lines except the first line of the file.