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Full Discussion: Question on bash redirection
Top Forums UNIX for Beginners Questions & Answers Question on bash redirection Post 303035997 by MadeInGermany on Wednesday 12th of June 2019 01:51:45 AM
Old 06-12-2019
x < y means: run command x and feed its input (stdin) from file y.
It is true that file y is opened for reading before command x runs.
diff <(sort testfile.txt) <(sort testfile2.txt) means: open a device ("/dev/fd/..."), run sort and redirect its output to the device, open another device, run another sort and redirect its output, run diff with the two devices as arguments (that diff treats as input filenames).
Quote:
man bash
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Process substitution
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The process list is run asynchronously, and its input or output appears as a filename. This filename is passed as an argument to the current command as the result of the expansion. If the >(list) form is used, writing to the file will provide input for list. If the <(list) form is used, the file passed as an argument should be read to obtain the output of list. Note that no space may appear between the < or > and the left parenthesis, otherwise the construct would be interpreted as a redirection. Process substitution is supported on systems that support named pipes (FIFOs) or the /dev/fd method of naming open files.
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bdiff(1)						      General Commands Manual							  bdiff(1)

NAME
bdiff - Finds differences in large files SYNOPSIS
bdiff file1 file2 [number] [-s] bdiff - file2 [number] [-s] bdiff file1 - [number] [-s] The bdiff command compares file1 and file2 and writes information about their differing lines to standard output. If either filename is - (dash), bdiff reads standard input. OPTIONS
Suppresses error messages. (May either precede or follow the number argument if it is specified.) DESCRIPTION
The bdiff command uses diff to find lines that must be changed in two files to make them identical (see the diff command). Its primary purpose is to permit processing of files that are too large for diff. The bdiff command ignores lines common to the beginning of both files, splits the remainders into sections of number lines, and runs diff on the sections. The output is then processed to make it look as if diff had processed the files whole. If you do not specify number, a system default is used. In some cases, the number you specify or the default number may be too large for diff. If bdiff fails, specify a smaller value for number and try again. Note that because of file segmenting, bdiff does not necessarily find the smallest possible set of file differences. In general, although the output is similar, using bdiff is not the equivalent of using diff. NOTES
The diff command is executed by a child process, generated by forking, and communicates with bdiff through pipes. It should not normally be necessary to use this command, since diff can handle most large files. EXIT STATUS
No differences. Differences found. An error occurred. SEE ALSO
Commands: diff(1), diff3(1) bdiff(1)
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