what is -u option in while loop in unix

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what is -u option in while loop in unix

Hi all,

What does -u option in while loop indicates in unix?

ex: while read -u field

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-u is a flag to 'read', not while. See your shell's man page to find what it does. In ksh -u should be followed by a file descriptor (ex: read -u3). It causes input to be read from the specified file descriptor (3 in the above example). -u without a file descriptor defaults to 0 - the standard input. You can also omit -u if reading from stdin.

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