.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 
.TH "CAT" P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" cat 
.SH NAME
cat \- concatenate and print files
.SH SYNOPSIS
.LP
\fBcat\fP \fB[\fP\fB-u\fP\fB][\fP\fIfile\fP \fB...\fP\fB]\fP
.SH DESCRIPTION
.LP
The \fIcat\fP utility shall read files in sequence and shall write
their contents to the standard output in the same
sequence.
.SH OPTIONS
.LP
The \fIcat\fP utility shall conform to the Base Definitions volume
of IEEE\ Std\ 1003.1-2001, Section 12.2, Utility Syntax Guidelines.
.LP
The following option shall be supported:
.TP 7
\fB-u\fP
Write bytes from the input file to the standard output without delay
as each is read.
.sp
.SH OPERANDS
.LP
The following operand shall be supported:
.TP 7
\fIfile\fP
A pathname of an input file. If no \fIfile\fP operands are specified,
the standard input shall be used. If a \fIfile\fP is
\fB'-'\fP , the \fIcat\fP utility shall read from the standard input
at that point in the sequence. The \fIcat\fP utility
shall not close and reopen standard input when it is referenced in
this way, but shall accept multiple occurrences of \fB'-'\fP
as a \fIfile\fP operand.
.sp
.SH STDIN
.LP
The standard input shall be used only if no \fIfile\fP operands are
specified, or if a \fIfile\fP operand is \fB'-'\fP .
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
\fIcat\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.
.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
The standard output shall contain the sequence of bytes read from
the input files. Nothing else shall be written to the standard
output.
.SH STDERR
.LP
The standard error shall be used only for diagnostic messages.
.SH OUTPUT FILES
.LP
None.
.SH EXTENDED DESCRIPTION
.LP
None.
.SH EXIT STATUS
.LP
The following exit values shall be returned:
.TP 7
\ 0
All input files were output successfully.
.TP 7
>0
An error occurred.
.sp
.SH CONSEQUENCES OF ERRORS
.LP
Default.
.LP
\fIThe following sections are informative.\fP
.SH APPLICATION USAGE
.LP
The \fB-u\fP option has value in prototyping non-blocking reads from
FIFOs. The intent is to support the following
sequence:
.sp
.RS
.nf

\fBmkfifo foo
cat -u foo > /dev/tty13 &
cat -u > foo
\fP
.fi
.RE
.LP
It is unspecified whether standard output is or is not buffered in
the default case. This is sometimes of interest when standard
output is associated with a terminal, since buffering may delay the
output. The presence of the \fB-u\fP option guarantees that
unbuffered I/O is available. It is implementation-defined whether
the \fIcat\fP utility buffers output if the \fB-u\fP option is
not specified. Traditionally, the \fB-u\fP option is implemented using
the equivalent of the \fIsetvbuf\fP() function defined in the System
Interfaces volume of
IEEE\ Std\ 1003.1-2001.
.SH EXAMPLES
.LP
The following command:
.sp
.RS
.nf

\fBcat myfile
\fP
.fi
.RE
.LP
writes the contents of the file \fBmyfile\fP to standard output.
.LP
The following command:
.sp
.RS
.nf

\fBcat doc1 doc2 > doc.all
\fP
.fi
.RE
.LP
concatenates the files \fBdoc1\fP and \fBdoc2\fP and writes the result
to \fBdoc.all\fP.
.LP
Because of the shell language mechanism used to perform output redirection,
a command such as this:
.sp
.RS
.nf

\fBcat doc doc.end > doc
\fP
.fi
.RE
.LP
causes the original data in \fBdoc\fP to be lost.
.LP
The command:
.sp
.RS
.nf

\fBcat start - middle - end > file
\fP
.fi
.RE
.LP
when standard input is a terminal, gets two arbitrary pieces of input
from the terminal with a single invocation of \fIcat\fP.
Note, however, that if standard input is a regular file, this would
be equivalent to the command:
.sp
.RS
.nf

\fBcat start - middle /dev/null end > file
\fP
.fi
.RE
.LP
because the entire contents of the file would be consumed by \fIcat\fP
the first time \fB'-'\fP was used as a \fIfile\fP
operand and an end-of-file condition would be detected immediately
when \fB'-'\fP was referenced the second time.
.SH RATIONALE
.LP
Historical versions of the \fIcat\fP utility include the options \fB-e\fP,
\fB-t\fP, and \fB-v\fP, which permit the ends of
lines, <tab>s, and invisible characters, respectively, to be rendered
visible in the output. The standard developers omitted
these options because they provide too fine a degree of control over
what is made visible, and similar output can be obtained using
a command such as:
.sp
.RS
.nf

\fBsed -n -e 's/$/$/' -e l pathname
\fP
.fi
.RE
.LP
The \fB-s\fP option was omitted because it corresponds to different
functions in BSD and System V-based systems. The BSD
\fB-s\fP option to squeeze blank lines can be accomplished by the
shell script shown in the following example:
.sp
.RS
.nf

\fBsed -n '
# Write non-empty lines.
/./   {
      p
      d
      }
# Write a single empty line, then look for more empty lines.
/^$/  p
# Get next line, discard the held <newline> (empty line),
# and look for more empty lines.
:Empty
/^$/  {
      N
      s/.//
      b Empty
      }
# Write the non-empty line before going back to search
# for the first in a set of empty lines.
      p
'
\fP
.fi
.RE
.LP
The System V \fB-s\fP option to silence error messages can be accomplished
by redirecting the standard error. Note that the BSD
documentation for \fIcat\fP uses the term "blank line" to mean the
same as the POSIX "empty line'': a line consisting only of a
<newline>.
.LP
The BSD \fB-n\fP option was omitted because similar functionality
can be obtained from the \fB-n\fP option of the \fIpr\fP utility.
.SH FUTURE DIRECTIONS
.LP
None.
.SH SEE ALSO
.LP
\fImore\fP , the System Interfaces volume of IEEE\ Std\ 1003.1-2001,
\fIsetvbuf\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 .