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The redirfd program

redirfd redirects a given file descriptor to a file, then executes a program.

Interface

     redirfd [ -r | -w | -u | -a | -c | -x ] [ -n ] [ -b ] fd file prog...

redirfd redirects the file descriptor number fd to file, then execs into prog....

Options

One and only one of the -r, -w, -u, -a, -c, or -x options must be given; the -n and -b options may be added in any case.

• -r : open file for reading.
• -w : open file for writing, truncating it if it already exists.
• -u : open file for reading and writing.
• -a : open file for appending, creating it if it doesn't exist.
• -c : open file for appending. Do not create it if it doesn't exist.
• -x : open file for writing, creating it, failing if it already exists.
• -n : open file in non-blocking mode.
• -b : change mode of file after opening it: to non-blocking mode if the -n option was not given, to blocking mode if it was.

Notes

• redirfd -r n file prog... is roughly equivalent to sh -c 'exec prog... n<file'
• redirfd -w n file prog... is roughly equivalent to sh -c 'exec prog... n>file'
• redirfd -u n file prog... is roughly equivalent to sh -c 'exec prog... n<>file'
• redirfd -a n file prog... is roughly equivalent to sh -c 'exec prog... n>>file'
• redirfd -c n file prog... has no portable shell equivalent. Some shells provide the noclobber option for a similar feature.
• redirfd -x n file prog... has no portable shell equivalent.

Special fifo handling

The -n and -b options are especially useful with named pipes.

• Opening a fifo for reading, blocking if there is no writer: redirfd -r n fifo prog...
• Opening a fifo for reading, with instant success even if there is no writer, and blocking at the first attempt to read from it: redirfd -r -nb n fifo prog...
• Opening a fifo for writing, blocking if there is no reader: redirfd -w n fifo prog...
• Opening a fifo for writing, with instant success even if there is no reader: redirfd -w -nb n fifo prog.... Warning: the first attempt to write to the fifo will raise a SIGPIPE if there is still no reader at that time. The named pipe semantics normally do not allow a fifo to be open for writing without a reading end, and you should know what you are doing if you're using redirfd this way.