fd dup (Marco’s Bash Functions Libraries)

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21.3 Duplicating file descriptors ¶

Function: mbfl_fd_dup_input SRCFD DSTFD ¶

Function: mbfl_fd_dup_output SRCFD DSTFD ¶

Duplicate the source file descriptor SRCFD to the destination file descriptor DSTFD.

If the predefined options --test or --show-program are enabled: print a line on the standard error channel describing the operation. If the predefined option --test is enabled: the file descriptor is still duplicated. Predefined options.

Let’s see how we can use a FIFO for reading and writing with two duplicate file descriptors:

mbfl_declare_program mkfifo
mbfl_file_enable_remove

function program_mkfifo () {
    local PATHNAME=${1:?}
    shift 1
    local MKFIFO
    mbfl_program_found_var MKFIFO mkfifo || exit_because_program_not_found

    "$MKFIFO" --mode=0600 "$@" "$PATHNAME"
}

declare TESTFILE=/path/to/fifo.ext
declare INFD=3 OUFD=4 DUP_INFD=5 DUP_OUFD=6
declare LINE1 LINE2 LINE3

mbfl_location_enter
{
    program_mkfifo "$TESTFIFO"
    mbfl_location_handler "mbfl_file_remove ${TESTFIFO}"

    mbfl_fd_open_input_output $INFD "$TESTFIFO"
    mbfl_location_handler "mbfl_fd_close ${INFD}"

    mbfl_fd_open_output $OUFD "$TESTFIFO"
    mbfl_location_handler "mbfl_fd_close ${OUFD}"

    echo 1234 >&${OUFD}
    read -u ${INFD} LINE1

    mbfl_location_enter
    {
        mbfl_fd_dup_input  $INFD $DUP_INFD
        mbfl_location_handler "mbfl_fd_close ${DUP_INFD}"

        mbfl_fd_dup_output $OUFD $DUP_OUFD
        mbfl_location_handler "mbfl_fd_close ${DUP_OUFD}"

        echo 5678 >&${DUP_OUFD}
        read -u ${DUP_INFD} LINE2
    }
    mbfl_location_leave

    echo 90 >&${OUFD}
    read -u ${INFD} LINE3
}
mbfl_location_leave

echo $LINE1 $LINE2 $LINE3

This document describes version 3.0.0-devel.9 of Marcos Bash Functions Library.