1HEAD(1P) POSIX Programmer's Manual HEAD(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 head - copy the first part of files
13
15 head [-n number][file...]
16
18 The head utility shall copy its input files to the standard output,
19 ending the output for each file at a designated point.
20 Copying shall end at the point in each input file indicated by the -n
22 number option. The option-argument number shall be counted in units of
23 lines.
24
26 The head utility shall conform to the Base Definitions volume of
27 IEEE Std 1003.1-2001, Section 12.2, Utility Syntax Guidelines.
28 The following option shall be supported:
30 -n number
32 The first number lines of each input file shall be copied to
33 standard output. The application shall ensure that the number
34 option-argument is a positive decimal integer.
35 When a file contains less than number lines, it shall be copied to
38 standard output in its entirety. This shall not be an error.
39 If no options are specified, head shall act as if -n 10 had been speci‐
41 fied.
42
44 The following operand shall be supported:
45 file A pathname of an input file. If no file operands are specified,
47 the standard input shall be used.
48
51 The standard input shall be used only if no file operands are speci‐
52 fied. See the INPUT FILES section.
53
55 Input files shall be text files, but the line length is not restricted
56 to {LINE_MAX} bytes.
57
59 The following environment variables shall affect the execution of head:
60 LANG Provide a default value for the internationalization variables
62 that are unset or null. (See the Base Definitions volume of
63 IEEE Std 1003.1-2001, Section 8.2, Internationalization Vari‐
64 ables for the precedence of internationalization variables used
65 to determine the values of locale categories.)
66 LC_ALL If set to a non-empty string value, override the values of all
68 the other internationalization variables.
69 LC_CTYPE
71 Determine the locale for the interpretation of sequences of
72 bytes of text data as characters (for example, single-byte as
73 opposed to multi-byte characters in arguments and input files).
74 LC_MESSAGES
76 Determine the locale that should be used to affect the format
77 and contents of diagnostic messages written to standard error.
78 NLSPATH
80 Determine the location of message catalogs for the processing of
81 LC_MESSAGES .
82
85 Default.
86
88 The standard output shall contain designated portions of the input
89 files.
90 If multiple file operands are specified, head shall precede the output
92 for each with the header:
93 "\n==> %s <==\n", <pathname>
96 except that the first header written shall not include the initial
98 <newline>.
99
101 The standard error shall be used only for diagnostic messages.
102
104 None.
105
107 None.
108
110 The following exit values shall be returned:
111 0 Successful completion.
113 >0 An error occurred.
115
118 Default.
119 The following sections are informative.
121
123 The obsolescent - number form is withdrawn in this version. Applica‐
124 tions should use the -n number option.
125
127 To write the first ten lines of all files (except those with a leading
128 period) in the directory:
129 head *
132
134 Although it is possible to simulate head with sed 10q for a single
135 file, the standard developers decided that the popularity of head on
136 historical BSD systems warranted its inclusion alongside tail.
137 This standard version of head follows the Utility Syntax Guidelines.
139 The -n option was added to this new interface so that head and tail
140 would be more logically related.
141 There is no -c option (as there is in tail) because it is not histori‐
143 cal practice and because other utilities in this volume of
144 IEEE Std 1003.1-2001 provide similar functionality.
145
147 None.
148
150 sed, tail
151
153 Portions of this text are reprinted and reproduced in electronic form
154 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
155 -- Portable Operating System Interface (POSIX), The Open Group Base
156 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
157 Electrical and Electronics Engineers, Inc and The Open Group. In the
158 event of any discrepancy between this version and the original IEEE and
159 The Open Group Standard, the original IEEE and The Open Group Standard
160 is the referee document. The original Standard can be obtained online
161 at http://www.opengroup.org/unix/online.html .
162IEEE/The Open Group 2003 HEAD(1P)