Meaning of "exec 9<name" in scripts

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# 1  
Old 11-22-2013
Meaning of "exec 9<name" in scripts

I have found code like

exec 9<filename

a number of times when looking over commonly used scripts here. What all does this do? Sometimes the filename is simply a list, but seems to always have read/write/execute attributes for all. I think the "<" means to accept this as input, but don't know about the 9.

# 2  
Old 11-22-2013
It opens a file descriptor (9 in this case) for reading, from file filename.
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# 3  
Old 11-22-2013
Standard input is file number 0, standard output is file number 1, and standard error is file number 2. Any other number can be used for whatever purpose you want -- in this case, they attach a file to it.
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# 4  
Old 11-22-2013
And, somewhat further down the script, you might find a read -u 9 (bash) or similar to actually input values from that descriptor.
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