Input-output functions

These functions enable sed scripts to read and write files directly:

p

The print function writes the contents of the pattern space (that is, any lines matching the desired address) to the standard output file at the time sed encounters the p function, regardless of what succeeding editing commands do to the lines. The maximum number of possible addresses is two.

wfile

The write function appends the addressed lines to file. If the file previously existed, it is overwritten; if not, it is created. The lines are written exactly as they exist when the write function is encountered for each line, regardless of what subsequent editing commands do to them. Exactly one space must separate the w function and the filename. The combined number of write functions and w flags may not exceed 10.

r

The read function reads the contents of the named file, and appends them after the line matched by the address. The file is read and appended regardless of what subsequent editing commands do to the line that matched its address. If r and a functions are executed on the same line, the text from the a functions and the r functions is written to the output in the order that the functions are executed. Exactly one space must separate the r and the filename; only one address is possible. If a file mentioned by an r function cannot be opened, it is considered a null file rather than an error, and no diagnostic is given.

You may have up to 20 appends in one script, and 10 w files open. These limits are built into sed.

In the example below, the file support.extensions contains the following list of telephone extensions:

   Fred:	x5706
   Marge:	x5631
   Sally:	x5239

   Thank you for enquiring about our customer support hotline.
   Please place your calls to our exchange at 346-4573, then
   dial one of the following extensions:
   

   phone list:

   Thank you for enquiring about our customer support hotline.
   Please place your calls to our exchange at 346-4573, then
   dial one of the following extensions:
   

   phone list:
   Fred:	x5706
   Marge:	x5631
   Sally:	x5239

Note, however, that the line matching the context address (in the example, the line consisting of the string ``phone list:'') must be terminated with a newline.