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Raku port of Perl's seek() built-in


use P5seek;

seek($filehandle, 42, 0);

seek($filehandle, 42, SEEK_SET); # same, SEEK_CUR / SEEK_END also available


This module tries to mimic the behaviour of Perl's seek built-in as closely as possible in the Raku Programming Language.


        Sets FILEHANDLE's position, just like the "fseek" call of "stdio".
        FILEHANDLE may be an expression whose value gives the name of the
        filehandle. The values for WHENCE are 0 to set the new position in
        bytes to POSITION; 1 to set it to the current position plus
        POSITION; and 2 to set it to EOF plus POSITION, typically
        negative. For WHENCE you may use the constants "SEEK_SET",
        "SEEK_CUR", and "SEEK_END" (start of the file, current position,
        end of the file) from the Fcntl module. Returns 1 on success,
        false otherwise.

        Note the in bytes: even if the filehandle has been set to operate
        on characters (for example by using the ":encoding(utf8)" open
        layer), tell() will return byte offsets, not character offsets
        (because implementing that would render seek() and tell() rather

        If you want to position the file for "sysread" or "syswrite",
        don't use "seek", because buffering makes its effect on the file's
        read-write position unpredictable and non-portable. Use "sysseek"

        Due to the rules and rigors of ANSI C, on some systems you have to
        do a seek whenever you switch between reading and writing. Amongst
        other things, this may have the effect of calling stdio's
        clearerr(3). A WHENCE of 1 ("SEEK_CUR") is useful for not moving
        the file position:


        This is also useful for applications emulating "tail -f". Once you
        hit EOF on your read and then sleep for a while, you (probably)
        have to stick in a dummy seek() to reset things. The "seek"
        doesn't change the position, but it does clear the end-of-file
        condition on the handle, so that the next "<FILE>" makes Perl try
        again to read something. (We hope.)

        If that doesn't work (some I/O implementations are particularly
        cantankerous), you might need something like this:

            for (;;) {
                for ($curpos = tell(FILE); $_ = <FILE>;
                     $curpos = tell(FILE)) {
                    # search for some stuff and put it into files
                seek(FILE, $curpos, 0);


For convenience, the terms SEEK_SET, SEEK_CUR and SEEK_END are also exported.


Elizabeth Mattijsen liz@raku.rocks

Source can be located at: https://github.com/lizmat/P5seek . Comments and Pull Requests are welcome.


Copyright 2018, 2019, 2020, 2021 Elizabeth Mattijsen

Re-imagined from Perl as part of the CPAN Butterfly Plan.

This library is free software; you can redistribute it and/or modify it under the Artistic License 2.0.