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
12 cat - concatenate and print files
13
15 cat [-u][file ...]
16
18 The cat utility shall read files in sequence and shall write their con‐
19 tents to the standard output in the same sequence.
20
22 The cat utility shall conform to the Base Definitions volume of
23 IEEE Std 1003.1-2001, Section 12.2, Utility Syntax Guidelines.
24 The following option shall be supported:
26 -u Write bytes from the input file to the standard output without
28 delay as each is read.
29
32 The following operand shall be supported:
33 file A pathname of an input file. If no file operands are specified,
35 the standard input shall be used. If a file is '-', the cat
36 utility shall read from the standard input at that point in the
37 sequence. The cat utility shall not close and reopen standard
38 input when it is referenced in this way, but shall accept multi‐
39 ple occurrences of '-' as a file operand.
40
43 The standard input shall be used only if no file operands are speci‐
44 fied, or if a file operand is '-' . See the INPUT FILES section.
45
47 The input files can be any file type.
48
50 The following environment variables shall affect the execution of cat:
51 LANG Provide a default value for the internationalization variables
53 that are unset or null. (See the Base Definitions volume of
54 IEEE Std 1003.1-2001, Section 8.2, Internationalization Vari‐
55 ables for the precedence of internationalization variables used
56 to determine the values of locale categories.)
57 LC_ALL If set to a non-empty string value, override the values of all
59 the other internationalization variables.
60 LC_CTYPE
62 Determine the locale for the interpretation of sequences of
63 bytes of text data as characters (for example, single-byte as
64 opposed to multi-byte characters in arguments).
65 LC_MESSAGES
67 Determine the locale that should be used to affect the format
68 and contents of diagnostic messages written to standard error.
69 NLSPATH
71 Determine the location of message catalogs for the processing of
72 LC_MESSAGES .
73
76 Default.
77
79 The standard output shall contain the sequence of bytes read from the
80 input files. Nothing else shall be written to the standard output.
81
83 The standard error shall be used only for diagnostic messages.
84
86 None.
87
89 None.
90
92 The following exit values shall be returned:
93 0 All input files were output successfully.
95 >0 An error occurred.
97
100 Default.
101 The following sections are informative.
103
105 The -u option has value in prototyping non-blocking reads from FIFOs.
106 The intent is to support the following sequence:
107 mkfifo foo
110 cat -u foo > /dev/tty13 &
111 cat -u > foo
112 It is unspecified whether standard output is or is not buffered in the
114 default case. This is sometimes of interest when standard output is
115 associated with a terminal, since buffering may delay the output. The
116 presence of the -u option guarantees that unbuffered I/O is available.
117 It is implementation-defined whether the cat utility buffers output if
118 the -u option is not specified. Traditionally, the -u option is imple‐
119 mented using the equivalent of the setvbuf() function defined in the
120 System Interfaces volume of IEEE Std 1003.1-2001.
121
123 The following command:
124 cat myfile
127 writes the contents of the file myfile to standard output.
129 The following command:
131 cat doc1 doc2 > doc.all
134 concatenates the files doc1 and doc2 and writes the result to doc.all.
136 Because of the shell language mechanism used to perform output redi‐
138 rection, a command such as this:
139 cat doc doc.end > doc
142 causes the original data in doc to be lost.
144 The command:
146 cat start - middle - end > file
149 when standard input is a terminal, gets two arbitrary pieces of input
151 from the terminal with a single invocation of cat. Note, however, that
152 if standard input is a regular file, this would be equivalent to the
153 command:
154 cat start - middle /dev/null end > file
157 because the entire contents of the file would be consumed by cat the
159 first time '-' was used as a file operand and an end-of-file condition
160 would be detected immediately when '-' was referenced the second time.
161
163 Historical versions of the cat utility include the options -e, -t, and
164 -v, which permit the ends of lines, <tab>s, and invisible characters,
165 respectively, to be rendered visible in the output. The standard devel‐
166 opers omitted these options because they provide too fine a degree of
167 control over what is made visible, and similar output can be obtained
168 using a command such as:
169 sed -n -e 's/$/$/' -e l pathname
172 The -s option was omitted because it corresponds to different functions
174 in BSD and System V-based systems. The BSD -s option to squeeze blank
175 lines can be accomplished by the shell script shown in the following
176 example:
177 sed -n '
180 # Write non-empty lines.
181 /./ {
182 p
183 d
184 }
185 # Write a single empty line, then look for more empty lines.
186 /^$/ p
187 # Get next line, discard the held <newline> (empty line),
188 # and look for more empty lines.
189 :Empty
190 /^$/ {
191 N
192 s/.//
193 b Empty
194 }
195 # Write the non-empty line before going back to search
196 # for the first in a set of empty lines.
197 p
198 The System V -s option to silence error messages can be accomplished by
200 redirecting the standard error. Note that the BSD documentation for cat
201 uses the term "blank line" to mean the same as the POSIX "empty line'':
202 a line consisting only of a <newline>.
203 The BSD -n option was omitted because similar functionality can be
205 obtained from the -n option of the pr utility.
206
208 None.
209
211 more, the System Interfaces volume of IEEE Std 1003.1-2001, setvbuf()
212
214 Portions of this text are reprinted and reproduced in electronic form
215 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
216 -- Portable Operating System Interface (POSIX), The Open Group Base
217 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
218 Electrical and Electronics Engineers, Inc and The Open Group. In the
219 event of any discrepancy between this version and the original IEEE and
220 The Open Group Standard, the original IEEE and The Open Group Standard
221 is the referee document. The original Standard can be obtained online
222 at http://www.opengroup.org/unix/online.html .
223IEEE/The Open Group 2003 CAT(1P)