Bash Quick Start Guide

Adding file contents to a stream

Sometimes, you may want to add header or footer information to a stream in a pipeline, perhaps read from another file. One straightforward way of doing this is using cat for its intended purpose of concatenating streams of input.

Normally, cat combines all of the filenames specified in its arguments and writes them to standard output, in the same order they were specified:

$ cat myfile1 myfile2 myfile3 > myfiles.combined

We can use the special value of a single hyphen (-) anywhere among the cat filename arguments to denote that any standard input to cat should be added at that point. For example, if we had a generate-html command that generated the body of an HTML document, we might want to add the headers ...