1CAT(1P) POSIX Programmer's Manual CAT(1P)
2
6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
10
13 cat — concatenate and print files
14
16 cat [−u] [file...]
17
19 The cat utility shall read files in sequence and shall write their con‐
20 tents to the standard output in the same sequence.
21
23 The cat utility shall conform to the Base Definitions volume of
24 POSIX.1‐2008, Section 12.2, Utility Syntax Guidelines.
25 The following option shall be supported:
27 −u Write bytes from the input file to the standard output with‐
29 out delay as each is read.
30
32 The following operand shall be supported:
33 file A pathname of an input file. If no file operands are speci‐
35 fied, the standard input shall be used. If a file is '−', the
36 cat utility shall read from the standard input at that point
37 in the sequence. The cat utility shall not close and reopen
38 standard input when it is referenced in this way, but shall
39 accept multiple occurrences of '−' as a file operand.
40
42 The standard input shall be used only if no file operands are speci‐
43 fied, or if a file operand is '−'. See the INPUT FILES section.
44
46 The input files can be any file type.
47
49 The following environment variables shall affect the execution of cat:
50 LANG Provide a default value for the internationalization vari‐
52 ables that are unset or null. (See the Base Definitions vol‐
53 ume of POSIX.1‐2008, Section 8.2, Internationalization Vari‐
54 ables for the precedence of internationalization variables
55 used to determine the values of locale categories.)
56 LC_ALL If set to a non-empty string value, override the values of
58 all the other internationalization variables.
59 LC_CTYPE Determine the locale for the interpretation of sequences of
61 bytes of text data as characters (for example, single-byte as
62 opposed to multi-byte characters in arguments).
63 LC_MESSAGES
65 Determine the locale that should be used to affect the format
66 and contents of diagnostic messages written to standard
67 error.
68 NLSPATH Determine the location of message catalogs for the processing
70 of LC_MESSAGES.
71
73 Default.
74
76 The standard output shall contain the sequence of bytes read from the
77 input files. Nothing else shall be written to the standard output.
78
80 The standard error shall be used only for diagnostic messages.
81
83 None.
84
86 None.
87
89 The following exit values shall be returned:
90 0 All input files were output successfully.
92 >0 An error occurred.
94
96 Default.
97 The following sections are informative.
99
101 The −u option has value in prototyping non-blocking reads from FIFOs.
102 The intent is to support the following sequence:
103 mkfifo foo
105 cat −u foo > /dev/tty13 &
106 cat −u > foo
107 It is unspecified whether standard output is or is not buffered in the
109 default case. This is sometimes of interest when standard output is
110 associated with a terminal, since buffering may delay the output. The
111 presence of the −u option guarantees that unbuffered I/O is available.
112 It is implementation-defined whether the cat utility buffers output if
113 the −u option is not specified. Traditionally, the −u option is imple‐
114 mented using the equivalent of the setvbuf() function defined in the
115 System Interfaces volume of POSIX.1‐2008.
116
118 The following command:
119 cat myfile
121 writes the contents of the file myfile to standard output.
123 The following command:
125 cat doc1 doc2 > doc.all
127 concatenates the files doc1 and doc2 and writes the result to doc.all.
129 Because of the shell language mechanism used to perform output redi‐
131 rection, a command such as this:
132 cat doc doc.end > doc
134 causes the original data in doc to be lost.
136 The command:
138 cat start − middle − end > file
140 when standard input is a terminal, gets two arbitrary pieces of input
142 from the terminal with a single invocation of cat. Note, however, that
143 if standard input is a regular file, this would be equivalent to the
144 command:
145 cat start − middle /dev/null end > file
147 because the entire contents of the file would be consumed by cat the
149 first time '−' was used as a file operand and an end-of-file condition
150 would be detected immediately when '−' was referenced the second time.
151
153 Historical versions of the cat utility include the −e, −t, and −v,
154 options which permit the ends of lines, <tab> characters, and invisible
155 characters, respectively, to be rendered visible in the output. The
156 standard developers omitted these options because they provide too fine
157 a degree of control over what is made visible, and similar output can
158 be obtained using a command such as:
159 sed −n l pathname
161 The latter also has the advantage that its output is unambiguous,
163 whereas the output of historical cat −etv is not.
164 The −s option was omitted because it corresponds to different functions
166 in BSD and System V-based systems. The BSD −s option to squeeze blank
167 lines can be accomplished by the shell script shown in the following
168 example:
169 sed −n '
171 # Write non-empty lines.
172 /./ {
173 p
174 d
175 }
176 # Write a single empty line, then look for more empty lines.
177 /^$/ p
178 # Get next line, discard the held <newline> (empty line),
179 # and look for more empty lines.
180 :Empty
181 /^$/ {
182 N
183 s/.//
184 b Empty
185 }
186 # Write the non-empty line before going back to search
187 # for the first in a set of empty lines.
188 p
189 '
190 The System V −s option to silence error messages can be accomplished by
192 redirecting the standard error. Note that the BSD documentation for cat
193 uses the term ``blank line'' to mean the same as the POSIX ``empty
194 line'': a line consisting only of a <newline>.
195 The BSD −n option was omitted because similar functionality can be
197 obtained from the −n option of the pr utility.
198
200 None.
201
203 more
204 The Base Definitions volume of POSIX.1‐2008, Chapter 8, Environment
206 Variables, Section 12.2, Utility Syntax Guidelines
207 The System Interfaces volume of POSIX.1‐2008, setvbuf()
209
211 Portions of this text are reprinted and reproduced in electronic form
212 from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
213 -- Portable Operating System Interface (POSIX), The Open Group Base
214 Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
215 cal and Electronics Engineers, Inc and The Open Group. (This is
216 POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
217 event of any discrepancy between this version and the original IEEE and
218 The Open Group Standard, the original IEEE and The Open Group Standard
219 is the referee document. The original Standard can be obtained online
220 at http://www.unix.org/online.html .
221 Any typographical or formatting errors that appear in this page are
223 most likely to have been introduced during the conversion of the source
224 files to man page format. To report such errors, see https://www.ker‐
225 nel.org/doc/man-pages/reporting_bugs.html .
226IEEE/The Open Group 2013 CAT(1P)