path: root/man1p/cmp.1p

.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 
.TH "CMP" P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" cmp 
.SH NAME
cmp \- compare two files
.SH SYNOPSIS
.LP
\fBcmp\fP \fB[\fP \fB-l | -s\fP \fB]\fP \fIfile1 file2\fP
.SH DESCRIPTION
.LP
The \fIcmp\fP utility shall compare two files. The \fIcmp\fP utility
shall write no output if the files are the same. Under
default options, if they differ, it shall write to standard output
the byte and line number at which the first difference occurred.
Bytes and lines shall be numbered beginning with 1.
.SH OPTIONS
.LP
The \fIcmp\fP utility shall conform to the Base Definitions volume
of IEEE\ Std\ 1003.1-2001, Section 12.2, Utility Syntax Guidelines.
.LP
The following options shall be supported:
.TP 7
\fB-l\fP
(Lowercase ell.) Write the byte number (decimal) and the differing
bytes (octal) for each difference.
.TP 7
\fB-s\fP
Write nothing for differing files; return exit status only.
.sp
.SH OPERANDS
.LP
The following operands shall be supported:
.TP 7
\fIfile1\fP
A pathname of the first file to be compared. If \fIfile1\fP is \fB'-'\fP
, the standard input shall be used.
.TP 7
\fIfile2\fP
A pathname of the second file to be compared. If \fIfile2\fP is \fB'-'\fP
, the standard input shall be used.
.sp
.LP
If both \fIfile1\fP and \fIfile2\fP refer to standard input or refer
to the same FIFO special, block special, or character
special file, the results are undefined.
.SH STDIN
.LP
The standard input shall be used only if the \fIfile1\fP or \fIfile2\fP
operand refers to standard input. See the INPUT FILES
section.
.SH INPUT FILES
.LP
The input files can be any file type.
.SH ENVIRONMENT VARIABLES
.LP
The following environment variables shall affect the execution of
\fIcmp\fP:
.TP 7
\fILANG\fP
Provide a default value for the internationalization variables that
are unset or null. (See the Base Definitions volume of
IEEE\ Std\ 1003.1-2001, Section 8.2, Internationalization Variables
for
the precedence of internationalization variables used to determine
the values of locale categories.)
.TP 7
\fILC_ALL\fP
If set to a non-empty string value, override the values of all the
other internationalization variables.
.TP 7
\fILC_CTYPE\fP
Determine the locale for the interpretation of sequences of bytes
of text data as characters (for example, single-byte as
opposed to multi-byte characters in arguments).
.TP 7
\fILC_MESSAGES\fP
Determine the locale that should be used to affect the format and
contents of diagnostic messages written to standard error and
informative messages written to standard output.
.TP 7
\fINLSPATH\fP
Determine the location of message catalogs for the processing of \fILC_MESSAGES
\&.\fP 
.sp
.SH ASYNCHRONOUS EVENTS
.LP
Default.
.SH STDOUT
.LP
In the POSIX locale, results of the comparison shall be written to
standard output. When no options are used, the format shall
be:
.sp
.RS
.nf

\fB"%s %s differ: char %d, line %d\\n",\fP \fIfile1\fP\fB,\fP \fIfile2\fP\fB,
    <\fP\fIbyte number\fP\fB>, <\fP\fIline number\fP\fB>
\fP
.fi
.RE
.LP
When the \fB-l\fP option is used, the format shall be:
.sp
.RS
.nf

\fB"%d %o %o\\n", <\fP\fIbyte number\fP\fB>, <\fP\fIdiffering byte\fP\fB>,
    <\fP\fIdiffering byte\fP\fB>
\fP
.fi
.RE
.LP
for each byte that differs. The first <\fIdiffering\ byte\fP> number
is from \fIfile1\fP while the second is from
\fIfile2\fP. In both cases, <\fIbyte\ number\fP> shall be relative
to the beginning of the file, beginning with 1.
.LP
No output shall be written to standard output when the \fB-s\fP option
is used.
.SH STDERR
.LP
The standard error shall be used only for diagnostic messages. If
\fIfile1\fP and \fIfile2\fP are identical for the entire
length of the shorter file, in the POSIX locale the following diagnostic
message shall be written, unless the \fB-s\fP option is
specified:
.sp
.RS
.nf

\fB"cmp: EOF on %s%s\\n", <\fP\fIname of shorter file\fP\fB>, <\fP\fIadditional info\fP\fB>
\fP
.fi
.RE
.LP
The <\fIadditional\ info\fP> field shall either be null or a string
that starts with a <blank> and contains no
<newline>s. Some implementations report on the number of lines in
this case.
.SH OUTPUT FILES
.LP
None.
.SH EXTENDED DESCRIPTION
.LP
None.
.SH EXIT STATUS
.LP
The following exit values shall be returned:
.TP 7
\ 0
The files are identical.
.TP 7
\ 1
The files are different; this includes the case where one file is
identical to the first part of the other.
.TP 7
>1
An error occurred.
.sp
.SH CONSEQUENCES OF ERRORS
.LP
Default.
.LP
\fIThe following sections are informative.\fP
.SH APPLICATION USAGE
.LP
Although input files to \fIcmp\fP can be any type, the results might
not be what would be expected on character special device
files or on file types not described by the System Interfaces volume
of IEEE\ Std\ 1003.1-2001. Since this volume of
IEEE\ Std\ 1003.1-2001 does not specify the block size used when doing
input, comparisons of character special files need
not compare all of the data in those files.
.LP
For files which are not text files, line numbers simply reflect the
presence of a <newline>, without any implication that
the file is organized into lines.
.SH EXAMPLES
.LP
None.
.SH RATIONALE
.LP
The global language in \fIUtility Description Defaults\fP indicates
that using two
mutually-exclusive options together produces unspecified results.
Some System V implementations consider the option usage:
.sp
.RS
.nf

\fBcmp -l -s ...
\fP
.fi
.RE
.LP
to be an error. They also treat:
.sp
.RS
.nf

\fBcmp -s -l ...
\fP
.fi
.RE
.LP
as if no options were specified. Both of these behaviors are considered
bugs, but are allowed.
.LP
The word \fBchar\fP in the standard output format comes from historical
usage, even though it is actually a byte number. When
\fIcmp\fP is supported in other locales, implementations are encouraged
to use the word \fIbyte\fP or its equivalent in another
language. Users should not interpret this difference to indicate that
the functionality of the utility changed between locales.
.LP
Some implementations report on the number of lines in the identical-but-shorter
file case. This is allowed by the inclusion of
the <\fIadditional\ info\fP> fields in the output format. The restriction
on having a leading <blank> and no
<newline>s is to make parsing for the filename easier. It is recognized
that some filenames containing white-space characters
make parsing difficult anyway, but the restriction does aid programs
used on systems where the names are predominantly well
behaved.
.SH FUTURE DIRECTIONS
.LP
None.
.SH SEE ALSO
.LP
\fIcomm\fP , \fIdiff\fP
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .