Книга: Fedora™ Unleashed, 2008 edition

Printing the Contents of a File with cat

Printing the Contents of a File with cat

Many of Fedora's shell commands manipulate text strings, so if you want to be able to feed them the contents of files, you need to be able to output those files as text. Enter the cat command, which prints the contents of any files you pass to it. Its most basic use is like this:

$ cat myfile.txt

That prints the contents of myfile.txt. For this use, there are two extra parameters that are often used: -n numbers the lines in the output, and -s ("squeeze") prints a maximum of one blank line at a time. That is, if your file has 1 line of text, 10 blank lines, 1 line of text, 10 blank lines, and so on, -s shows the first line of text, a single blank line, the next line of text, a single blank line, and so forth. When you combine -s and -n, cat numbers only the lines that are printed — the 10 blank lines shown as one will count as 1 line for numbering.

This command prints information about your CPU, stripping out multiple blank lines and numbering the output:

$ cat -sn /proc/cpuinfo

You can also use cat to print the contents of several files at once, like this:

$ cat -s myfile.txt myotherfile.txt

In that command, cat merges myfile.txt and myotherfile.txt on the output, stripping out multiple blank lines. The important thing is that cat does not distinguish between the files in the output — no filenames are printed, and no extra breaks between the two files. This allows you to treat the two as one or, by adding more files to the command line, to treat 20 files as 1.

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