The wc utility shall read one or more input files and, by default, write
the number of <newline>s, words, and bytes contained in each input file
to the standard output.
The utility also shall write a total count for all named files, if more than one
input file is specified.
The wc utility shall consider a word to be a non-zero-length
string of characters delimited by white space.
The following environment variables shall affect the execution of wc:
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.)
If set to a non-empty string value, override the values of
all the other internationalization variables.
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 and input files) and which characters
are defined as white space characters.
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.
Determine the location of message catalogs for the
processing of LC_MESSAGES.
If the -m option is specified, the number of characters shall replace the
< bytes> field in this format.
If any options are specified and the -l option is not specified, the
number of <newline>s shall not be written.
If any options are specified and the -w option is not specified, the
number of words shall not be written.
If any options are specified and neither -c nor -m is specified,
the number of bytes or characters shall not be written.
If no input file operands are specified, no name shall be written and no
<blank>s preceding the pathname shall be written.
If more than one input file operand is specified, an additional line
shall be written, of the same format as the other lines, except that the word
total (in the POSIX locale) shall be written instead of a pathname and
the total of each column shall be written as appropriate. Such an additional
line, if any, is written at the end of the output.
The output file format pseudo- printf() string differs from the System V
version of wc:
which produces possibly ambiguous and unparsable results for very large files,
as it assumes no number shall exceed six digits.
Some historical implementations use only <space>, <tab>, and
<newline> as word separators. The equivalent of the ISO C
standard isspace() function is more appropriate.
The -c option stands for "character" count, even though it
counts bytes. This stems from the sometimes erroneous historical view that
bytes and characters are the same size. Due to international requirements, the
-m option (reminiscent of "multi-byte") was added to obtain
actual character counts.
Early proposals only specified the results when input files were text files. The
current specification more closely matches historical practice. (Bytes, words,
and <newline>s are counted separately and the results are written when
an end-of-file is detected.)
Historical implementations of the wc utility only accepted one argument
to specify the options -c, -l, and -w. Some of them also
had multiple occurrences of an option cause the corresponding count to be
written multiple times and had the order of specification of the options
affect the order of the fields on output, but did not document either of
these. Because common usage either specifies no options or only one option,
and because none of this was documented, the changes required by this volume
of IEEE Std 1003.1-2001 should not break many historical
applications (and do not break any historical conforming applications).
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