5.4. awk Commands from within a File
If awk commands are placed in a file, the -f option is used with the name of the awk file, followed by the name of the input file to be processed. A record is read into awk's buffer and each of the commands in the awk file are tested and executed for that record. After awk has finished with the first record, it is discarded and the next record is read into the buffer, and so on. If an action is not controlled by a pattern, the default behavior is to print the entire record. If a pattern does not have an action associated with it, the default is to print the record where the pattern matches an input line.
Example 5.13.
(The Database) $1 $2 $3 $4 $5 Tom Jones 4424 5/12/66 543354 Mary Adams 5346 11/4/63 28765 Sally Chang 1654 7/22/54 650000 Billy Black 1683 9/23/44 336500 % cat awkfile 1 /^Mary/{print "Hello Mary!"} 2 {print $1, $2, $3} 3 % awk -f awkfile employees Tom Jones 4424 Hello Mary! Mary Adams 5346 Sally Chang 1654 Billy Black 1683 4 % awk -W source '/^Sally/' -f awkfile employees Tom Jones 4424 Hello Mary! Mary Adams 5346 Sally Chang 1654 7/22/54 650000 Sally Chang 1654 Billy Black 1683 |
Explanation
If the record begins with the regular expression Mary, the string "Hello Mary!" is printed. The action is controlled by the pattern preceding it. Fields are separated by white space.
The first, second, and third field of each record are printed. The action occurs for each line because there is not a pattern controlling the action.
Awk reads commands from the script, awkfile.
When the -W option (specific to gawk) is followed by the argument, source, awk can intermix awk commands provided at the command line as well as those coming from a script file when the script file is preceded by the -f option. In this example, awk will search for Sally at the beginning of the line, and then get the rest of its commands from awkfile. The -W option is provided with Gnu awk, not UNIX versions of awk.