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Linux Shell Scripting with Bash

Extremely helpful site.

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Example: grep -f <(ls -1) /var/log/filelist.log
Example: cat textfile > >(wc -l)
<(list) will substitute on-the-fly with a FIFO, which can be read to obtain the output of list
>(list) will substitute on-the-fly with a FIFO, which can be written to, and list will read the content as if it is from console input

exec 3< filename; read LINE <&3; Open filename as input and assign to file descriptor number 3
3< filename; read LINE <&3; Open filename as input and assign to file descriptor number 3. But once assigned, 3 cannot be reassigned nor the file can be reopened.
exec 4<&3 Copy an input file descriptor. If 4 is omitted, 0 is assumed (as for input file descriptor)
exec 4<&3- Copy input file descriptor 3 to file descriptor 4, then close file descriptor 3.
exec 4>&3 Copy output file descriptor
exec 4>log.txt ; command >&4 Use of output file descriptor
exec 3<>filename Open a file for both input and output. But if you output something at the middle, the content pending for input will be overwritten. Think of a file position pointer concept.
exec 3<&- Close input file descriptor
exec 4>&- Close output file descriptor
/dev/fd/n Refer to file descriptor n
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