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A page for each applet in the kit, plus .so stubs for aliases such as egrep and unxz. Each was written from the pinned busybox-w32 source with the kit's patches and configuration, then checked against the source and by experiment. The NOTES sections cover Windows behavior. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
225 lines
5.2 KiB
Groff
225 lines
5.2 KiB
Groff
.TH SUM 1 2026-10-19 "w64devkit" "w64devkit Manual"
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.SH NAME
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sum \- print a 16-bit checksum and block count of files
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.SH SYNOPSIS
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.B sum
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.RB [ \-rs ]
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.RI [ file ...]
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.SH DESCRIPTION
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.B sum
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prints a 16-bit checksum and the size in blocks of each
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.IR file ,
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by one of two traditional algorithms.
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With no
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.I file
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operands, or for a
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.I file
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named
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.BR \- ,
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it reads standard input.
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.PP
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The options choose the algorithm and the block size.
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Bytes are unsigned in both.
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.TP
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BSD
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Used by default and with
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.BR \-r .
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The checksum starts at zero.
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For each byte it is rotated right by one bit within 16 bits, the byte is
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added, and the result is cut to 16 bits.
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The size is in blocks of 1024 bytes.
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.TP
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System V
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Used with
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.BR \-s .
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The checksum is the sum of all the bytes, kept to 32 bits.
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It is reduced to 16 bits by adding its high half to its low half, and
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then again to absorb the carry.
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The size is in blocks of 512 bytes.
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.PP
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A size is rounded up to a whole block, so empty input has size 0.
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.PP
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Each BSD line is the checksum as 5 digits with leading zeros, a space,
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the size right-aligned in at least 5 columns, a space, and the file name
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as given
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on the command line.
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The name is printed only when there is more than one operand.
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With one operand, or none, nothing follows the last space.
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.PP
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Each System V line is the checksum, a space, the size, a space, and the
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name.
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The name is always printed, as
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.B \-
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when standard input is read because there are no operands.
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.PP
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A file that cannot be opened or read is reported on standard error and
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has no output line.
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The remaining files are still processed.
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.SH OPTIONS
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Options may be grouped, as in
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.BR \-rs ,
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and may follow the operands unless
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.B POSIXLY_CORRECT
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is set.
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.B \-\-
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ends the options.
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There are no long options besides
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.BR \-\-help .
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.TP
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.B \-r
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Use the BSD algorithm and 1024-byte blocks.
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This is the default.
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It wins over
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.B \-s
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wherever the two appear, so
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.B \-sr
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and
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.B \-rs
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both select it.
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.TP
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.B \-s
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Use the System V algorithm and 512-byte blocks.
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.TP
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.B \-\-help
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Print a usage message on standard output and exit with status 0.
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It is recognized only as the first argument.
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.SH ENVIRONMENT
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.TP
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.B BB_CRITICAL_ERROR_DIALOGS
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When it is
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.BR 1 ,
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Windows shows its critical-error dialog for an operand on a drive with
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no disk in it.
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Otherwise the file fails to open.
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.TP
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.B BB_GLOBBING
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Unless it is
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.BR 0 ,
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wildcards in the operands are expanded as the program starts, as needed
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when run from
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.BR cmd.exe .
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A busybox process started with it unset sets it to
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.B 0
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for its children, so commands run from the kit's shell receive their
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operands as the shell expanded them.
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.TP
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.BR LC_ALL ", " LC_CTYPE ", " LANG
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If the first of these that is set has the value
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.BR C ,
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output to a console is not converted, and the console interprets the
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bytes of file names in its own code page.
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.TP
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.B POSIXLY_CORRECT
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If set, the first operand ends the options.
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.PP
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Variables that affect every busybox applet, such as
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.B BB_TERMINAL_MODE
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for console output, are described in
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.BR busybox (1).
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.SH EXIT STATUS
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.TP
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.B 0
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Every file was summed, or
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.B \-\-help
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was given.
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.TP
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.B 1
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A file could not be opened or read, or the command line was invalid.
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An invalid option also prints a usage message on standard error.
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.TP
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.B 141
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Standard output is a pipe whose reader exited before all output was
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written.
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If the pipe breaks only when the output still buffered at exit is
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written, or standard output fails in any other way, the status is not
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affected.
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.PP
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A file that cannot be opened is reported on standard error as
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.PP
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.RS 4
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.EX
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sum: can\(aqt open \(aq\fIfile\fR\(aq: \fIreason\fR
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.EE
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.RE
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.PP
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and an error while reading as
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.PP
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.RS 4
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.EX
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sum: \fIfile\fR: \fIreason\fR
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.EE
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.RE
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.SH EXAMPLES
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Checksum the output of a command with the System V algorithm:
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.PP
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.RS 4
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.EX
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$ printf abc | sum \-s
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294 1 \-
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.EE
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.RE
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.PP
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Checksum two files, which makes the BSD form print their names:
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.PP
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.RS 4
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.EX
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$ sum a.txt b.txt
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16556 1 a.txt
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36979 1 b.txt
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.EE
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.RE
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.PP
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Print only the checksum of one file:
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.PP
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.RS 4
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.EX
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$ sum a.txt | cut \-d\(aq \(aq \-f1
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16556
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.EE
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.RE
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.SH NOTES
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Both checksums are weak.
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They miss many changes and do not resist tampering.
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Use
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.BR sha256sum (1)
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or another digest where it matters.
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.PP
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.B \-s
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is GNU
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.BR sum 's
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.BR \-\-sysv .
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.PP
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Files and standard input are read as binary, so the checksum covers the
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exact bytes.
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A text file with CR LF line endings has a different checksum from a copy
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with LF line endings.
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Output lines end with LF.
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.PP
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Standard input is not closed after it is read.
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A second
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.B \-
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operand reads what remains, which at end of file is nothing, so its
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checksum and size are 0.
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.PP
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A directory operand fails with
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.BR "Permission denied" .
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.PP
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.I file
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may be a Windows path, with a drive letter and either kind of slash, or
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a busybox-w32 device name such as
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.IR /dev/null .
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It is printed exactly as given.
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On Windows 10 version 1903 or later, file names may contain any Unicode
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characters, and on older systems only those of the system code page.
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.PP
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Wildcards are expanded by the C runtime when busybox starts, even in
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quoted operands; see
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.BR BB_GLOBBING .
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A pattern that matches nothing is left as it is, and fails with
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.BR "Invalid argument" .
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.SH SEE ALSO
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.BR busybox (1),
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.BR cksum (1),
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.BR md5sum (1),
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.BR sha256sum (1)
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