Command-Line Syntax

You invoke sed and awk in much the same way. The command-line syntax is:

command [options] script filename

Like almost all UNIX programs, sed and awk can take input from standard input and send the output to standard output. If a filename is specified, input is taken from that file. The output contains the processed information. Standard output is the display screen, and typically the output from these programs is directed there. It can also be sent to a file, using I/O redirection in the shell, but it must not go to the same file that supplies input to the program.

The options for each command are different. We will demonstrate many of these options in upcoming sections. (The complete list of command-line options for sed can be found in Appendix A; the complete list of options for awk is in Appendix B.)

The script specifies what instructions to perform. If specified on the command line, the script must be surrounded in single quotes if it contains a space or any characters that might be interpreted by the shell ($ and * for instance).

One option common to both sed and awk is the -f option that allows you to specify the name of a script file. As a script grows in size, it is convenient to place it in a file. Thus, you might invoke sed as follows:

sed -f scriptfile inputfile

Figure 2.1 shows the basic operation of sed and awk. Each program reads one input line at a time from the input file, makes a copy of the input line, and executes the instructions ...

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