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Avalanche-io / c4

Go package implementation of C4 Asset ID
http://www.cccc.io/
MIT License
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ID while copying `cp` replacement #8

Closed mrjoshuak closed 7 years ago

mrjoshuak commented 8 years ago

First a cp clone that IDs the copied file on the fly, then add multiple destinations.

Ideally this will work just as fast as regular cp in the single target case, and faster then cp in the muilti-target case if the targets are on different IO busses / devices.

c4 cp should act as a drop in replacement for standard cp, so it must match feature for feature except for id reporting and a new flag to support multiple targets.

It would be nice to have comparative performance tests as part of this as well.

mrjoshuak commented 8 years ago

For reference the man pages for cp:

CP(1) BSD General Commands Manual CP(1)

NAME

 cp -- copy files

SYNOPSIS

 cp [-R [-H | -L | -P]] [-fi | -n] [-apvX] source_file target_file
 cp [-R [-H | -L | -P]] [-fi | -n] [-apvX] source_file ... target_directory

DESCRIPTION

In the first synopsis form, the cp utility copies the contents of the source_file to the target_file. In the second synopsis form, the contents of each named source_file is copied to the destination target_directory. The names of the files themselves are not changed. If cp detects an attempt to copy a file to itself, the copy will fail.

The following options are available:

 -a    Same as -pPR options. Preserves structure and attributes of files but not directory structure.

 -f    If the destination file cannot be opened, remove it and create a new file, without prompting for confirmation regardless of its permissions.  (The
       -f option overrides any previous -n option.)

       The target file is not unlinked before the copy.  Thus, any existing access rights will be retained.

 -H    If the -R option is specified, symbolic links on the command line are followed.  (Symbolic links encountered in the tree traversal are not fol-
       lowed.)

 -i    Cause cp to write a prompt to the standard error output before copying a file that would overwrite an existing file.  If the response from the
       standard input begins with the character `y' or `Y', the file copy is attempted.  (The -i option overrides any previous -n option.)

 -L    If the -R option is specified, all symbolic links are followed.

 -n    Do not overwrite an existing file.  (The -n option overrides any previous -f or -i options.)

 -P    If the -R option is specified, no symbolic links are followed.  This is the default.

 -p    Cause cp to preserve the following attributes of each source file in the copy: modification time, access time, file flags, file mode, user ID, and
       group ID, as allowed by permissions.  Access Control Lists (ACLs) and Extended Attributes (EAs), including resource forks, will also be preserved.

       If the user ID and group ID cannot be preserved, no error message is displayed and the exit value is not altered.

       If the source file has its set-user-ID bit on and the user ID cannot be preserved, the set-user-ID bit is not preserved in the copy's permissions.
       If the source file has its set-group-ID bit on and the group ID cannot be preserved, the set-group-ID bit is not preserved in the copy's permis-
       sions.  If the source file has both its set-user-ID and set-group-ID bits on, and either the user ID or group ID cannot be preserved, neither the
       set-user-ID nor set-group-ID bits are preserved in the copy's permissions.

 -R    If source_file designates a directory, cp copies the directory and the entire subtree connected at that point.  If the source_file ends in a /,
       the contents of the directory are copied rather than the directory itself.  This option also causes symbolic links to be copied, rather than indi-
       rected through, and for cp to create special files rather than copying them as normal files.  Created directories have the same mode as the corre-
       sponding source directory, unmodified by the process' umask.

       In -R mode, cp will continue copying even if errors are detected.

       Note that cp copies hard-linked files as separate files.  If you need to preserve hard links, consider using tar(1), cpio(1), or pax(1) instead.

 -v    Cause cp to be verbose, showing files as they are copied.

 -X    Do not copy Extended Attributes (EAs) or resource forks.

For each destination file that already exists, its contents are overwritten if permissions allow. Its mode, user ID, and group ID are unchanged unless the -p option was specified.

In the second synopsis form, target_directory must exist unless there is only one named source_file which is a directory and the -R flag is specified.

If the destination file does not exist, the mode of the source file is used as modified by the file mode creation mask (umask, see csh(1)). If the source file has its set-user-ID bit on, that bit is removed unless both the source file and the destination file are owned by the same user. If the source file has its set-group-ID bit on, that bit is removed unless both the source file and the destination file are in the same group and the user is a member of that group. If both the set-user-ID and set-group-ID bits are set, all of the above conditions must be fulfilled or both bits are removed.

Appropriate permissions are required for file creation or overwriting.

Symbolic links are always followed unless the -R flag is set, in which case symbolic links are not followed, by default. The -H or -L flags (in conjunction with the -R flag) cause symbolic links to be followed as described above. The -H, -L and -P options are ignored unless the -R option is specified. In addition, these options override each other and the command's actions are determined by the last one specified.

If cp receives a SIGINFO (see the status argument for stty(1)) signal, the current input and output file and the percentage complete will be written to the standard output.

EXIT STATUS

The cp utility exits 0 on success, and >0 if an error occurs.

COMPATIBILITY

Historic versions of the cp utility had a -r option. This implementation supports that option; however, its use is strongly discouraged, as it does not correctly copy special files, symbolic links, or fifo's.

The -v and -n options are non-standard and their use in scripts is not recommended.

LEGACY DESCRIPTION

In legacy mode, -f will override -i. Also, under the -f option, the target file is always unlinked before the copy. Thus, new access rights will always be set.

In -R mode, copying will terminate if an error is encountered.

For more information about legacy mode, see compat(5).

SEE ALSO

mv(1), rcp(1), umask(2), fts(3), compat(5), symlink(7)

STANDARDS

The cp command is expected to be IEEE Std 1003.2 (``POSIX.2'') compatible.

HISTORY

A cp command appeared in Version 1 AT&T UNIX.

BSD February 23, 2005 BSD