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Full Discussion: while read loop; scope of variables (shell)
Top Forums Shell Programming and Scripting while read loop; scope of variables (shell) Post 302293625 by mjd_tech on Tuesday 3rd of March 2009 01:32:10 PM
Old 03-03-2009
Ah! (light bulb turns on inside head)
I get it now.
I was thinking the "line" variable would hold the last line read.

so with:
while read line ; do some-command ; done < some-file

"read" tries to read the next line after the end of file, which is null,
and sets "line" to null, and returns "false" so the loop will end.

The "line" variable is not "invisible" outside the loop,
it just looks like that because it ends up null.

Just to make sure,
Code:
while [ "$line" != "Fred" ]; do
    read line
done << EOF
Wilma
Barney
Fred
Betty
EOF

echo "Line = $line"

The result is "Fred" in both bash and dash.

I've used this method before, but never really understood how it worked.

Thanks.

-MD
 

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LEARN ABOUT NETBSD

line

line(1)                                                            User Commands                                                           line(1)

NAME

       line - read one line

SYNOPSIS

       line

DESCRIPTION

       The  line utility copies one line (up to and including a new-line) from the standard input and writes it on the standard output. It returns
       an exit status of 1 on EOF and always prints at least a new-line. It is often used within shell files to read from the user's terminal.

EXIT STATUS

       Exit status is:

       0        Successful completion

       >0       End-of-file on input.

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE         |      ATTRIBUTE VALUE        |
       +-----------------------------+-----------------------------+
       |Availability                 |SUNWcsu                      |
       +-----------------------------+-----------------------------+

SEE ALSO

       sh(1), read(2), attributes(5)

SunOS 5.10                                                          1 Feb 1995                                                             line(1)
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