Linux tip: Using the read command

If you write shell scripts, this is one cool builtin Linux command you should know.

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The read builtin returns an exit status of 0 if it successfully reads any data. It has a nonzero exit status when it reaches the EOF (end of file).

The following example runs a while loop from the command line. It takes its input from the names file and terminates after reading the last line from names.

$ cat names
Alice Jones
Robert Smith
Alice Paulson
John Q. Public

$ while read first rest
> do
> echo $rest, $first
> done < names

Jones, Alice
Smith, Robert
Paulson, Alice
Q. Public, John
$

The placement of the redirection symbol (<) for the while structure is critical. It is important that you place the redirection symbol at the done statement and not at the call to read.

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