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Running AWK programs from the source file
When AWK programs are long, it is more convenient to put them in a separate file. Putting AWK programs in a file reduces errors and retyping. Its syntax is as follows:
$ awk -f source_file inputfile1 inputfile2 ............inputfileN
The -f option tells the AWK utility to read the AWK commands from source_file. Any filename can be used in place of source_file. For example, we can create a cmd.awk text file containing the AWK commands, as follows:
$ vi cmd.awk
BEGIN { print "***Emp Info***" }
{ print }
Now, we instruct AWK to read the commands from the cmd.awk file and perform the given actions:
$ awk -f cmd.awk empinfo.txt
On executing the preceding command, we get the following result:
***Emp Info***
Jack 9857532312 jack@gmail.com hr 2000 5
Jane 9837432312 jane@gmail.com hr 1800 5
Eva 8827232115 eva@gmail.com lgs 2100 6
amit 9911887766 amit@yahoo.com lgs 2350 6
Julie 8826234556 julie@yahoo.com hr 2500 5
It does the same thing as this:
$ awk 'BEGIN { print "***Emp Info***" } { print }' empinfo.txt
We don't usually need to put the filename specified with -f in single quotes, because filenames generally don't contain any shell special characters. In the cmd.awk source file, we didn't put the AWK commands in single quotes. The quotes are only needed when we execute the AWK command from the command line. We added the .awk extension in the filename to clearly identify the AWK program file; it doesn't affect the execution of the AWK program and hence is not mandatory.