sed & awk, 2nd Edition

Using awk

Like sed, awk executes a set of instructions for each line of input. You can specify instructions on the command line or create a script file.

Running awk

For command lines, the syntax is:

awk 'instructions' files

Input is read a line at a time from one or more files or from standard input. The instructions must be enclosed in single quotes to protect them from the shell. (Instructions almost always contain curly braces and/or dollar signs, which are interpreted as special characters by the shell.) Multiple command lines can be entered in the same way as shown for sed: separating commands with semicolons or using the multiline input capability of the Bourne shell.

Awk programs are usually placed in a file where they can be tested and modified. The syntax for invoking awk with a script file is:

awk -f script files

The -f option works the same way as it does with sed.

While awk instructions have the same structure as sed, consisting of pattern and procedure sections, the procedures themselves are quite different. Here is where awk looks less like an editor and more like a programming language. There are statements and functions instead of one- or two-character command sequences. For instance, you use the print statement to print the value of an expression or to print the contents of the current input line.

Awk, in the usual case, interprets each input line as a record and each word on that line, delimited by spaces or tabs, as a field. (These defaults can be changed.) One ...