HEAD(1)                    POSIX Programmer's Manual                   HEAD(1)



PPRROOLLOOGG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

NNAAMMEE
       head -- copy the first part of files

SSYYNNOOPPSSIISS
       head [[-n _n_u_m_b_e_r]] [[_f_i_l_e...]]

DDEESSCCRRIIPPTTIIOONN
       The _h_e_a_d utility shall copy its input files to the standard output,
       ending the output for each file at a designated point.

       Copying shall end at the point in each input file indicated by the --nn
       _n_u_m_b_e_r option. The option-argument _n_u_m_b_e_r shall be counted in units of
       lines.

OOPPTTIIOONNSS
       The _h_e_a_d utility shall conform to the Base Definitions volume of
       POSIX.1-2017, _S_e_c_t_i_o_n _1_2_._2, _U_t_i_l_i_t_y _S_y_n_t_a_x _G_u_i_d_e_l_i_n_e_s.

       The following option shall be supported:

       --nn _n_u_m_b_e_r The first _n_u_m_b_e_r lines of each input file shall be copied to
                 standard output. The application shall ensure that the _n_u_m_b_e_r
                 option-argument is a positive decimal integer.

       When a file contains less than _n_u_m_b_e_r lines, it shall be copied to
       standard output in its entirety. This shall not be an error.

       If no options are specified, _h_e_a_d shall act as if --nn 1100 had been
       specified.

OOPPEERRAANNDDSS
       The following operand shall be supported:

       _f_i_l_e      A pathname of an input file. If no _f_i_l_e operands are
                 specified, the standard input shall be used.

SSTTDDIINN
       The standard input shall be used if no _f_i_l_e operands are specified, and
       shall be used if a _f_i_l_e operand is ''--'' and the implementation treats
       the ''--'' as meaning standard input.  Otherwise, the standard input shall
       not be used.  See the INPUT FILES section.

IINNPPUUTT FFIILLEESS
       Input files shall be text files, but the line length is not restricted
       to {LINE_MAX} bytes.

EENNVVIIRROONNMMEENNTT VVAARRIIAABBLLEESS
       The following environment variables shall affect the execution of _h_e_a_d:

       _L_A_N_G      Provide a default value for the internationalization
                 variables that are unset or null. (See the Base Definitions
                 volume of POSIX.1-2017, _S_e_c_t_i_o_n _8_._2, _I_n_t_e_r_n_a_t_i_o_n_a_l_i_z_a_t_i_o_n
                 _V_a_r_i_a_b_l_e_s for the precedence of internationalization
                 variables used to determine the values of locale categories.)

       _L_C___A_L_L    If set to a non-empty string value, override the values of
                 all the other internationalization variables.

       _L_C___C_T_Y_P_E  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).

       _L_C___M_E_S_S_A_G_E_S
                 Determine the locale that should be used to affect the format
                 and contents of diagnostic messages written to standard
                 error.

       _N_L_S_P_A_T_H   Determine the location of message catalogs for the processing
                 of _L_C___M_E_S_S_A_G_E_S.

AASSYYNNCCHHRROONNOOUUSS EEVVEENNTTSS
       Default.

SSTTDDOOUUTT
       The standard output shall contain designated portions of the input
       files.

       If multiple _f_i_l_e operands are specified, _h_e_a_d shall precede the output
       for each with the header:


           "\n==> %s <==\n", <_p_a_t_h_n_a_m_e>

       except that the first header written shall not include the initial
       <newline>.

SSTTDDEERRRR
       The standard error shall be used only for diagnostic messages.

OOUUTTPPUUTT FFIILLEESS
       None.

EEXXTTEENNDDEEDD DDEESSCCRRIIPPTTIIOONN
       None.

EEXXIITT SSTTAATTUUSS
       The following exit values shall be returned:

        0    Successful completion.

       >0    An error occurred.

CCOONNSSEEQQUUEENNCCEESS OOFF EERRRROORRSS
       Default.

       _T_h_e _f_o_l_l_o_w_i_n_g _s_e_c_t_i_o_n_s _a_r_e _i_n_f_o_r_m_a_t_i_v_e_.

AAPPPPLLIICCAATTIIOONN UUSSAAGGEE
       When using _h_e_a_d to process pathnames, it is recommended that LC_ALL, or
       at least LC_CTYPE and LC_COLLATE, are set to POSIX or C in the
       environment, since pathnames can contain byte sequences that do not
       form valid characters in some locales, in which case the utility's
       behavior would be undefined. In the POSIX locale each byte is a valid
       single-byte character, and therefore this problem is avoided.

EEXXAAMMPPLLEESS
       To write the first ten lines of all files (except those with a leading
       period) in the directory:


           head -- *

RRAATTIIOONNAALLEE
       Although it is possible to simulate _h_e_a_d with _s_e_d 10q for a single
       file, the standard developers decided that the popularity of _h_e_a_d on
       historical BSD systems warranted its inclusion alongside _t_a_i_l.

       POSIX.1-2008 version of _h_e_a_d follows the Utility Syntax Guidelines. The
       --nn option was added to this new interface so that _h_e_a_d and _t_a_i_l would
       be more logically related. Earlier versions of this standard allowed a
       --nnuummbbeerr option. This form is no longer specified by POSIX.1-2008 but
       may be present in some implementations.

       There is no --cc option (as there is in _t_a_i_l) because it is not
       historical practice and because other utilities in this volume of
       POSIX.1-2017 provide similar functionality.

FFUUTTUURREE DDIIRREECCTTIIOONNSS
       None.

SSEEEE AALLSSOO
       _s_e_d, _t_a_i_l

       The Base Definitions volume of POSIX.1-2017, _C_h_a_p_t_e_r _8, _E_n_v_i_r_o_n_m_e_n_t
       _V_a_r_i_a_b_l_e_s, _S_e_c_t_i_o_n _1_2_._2, _U_t_i_l_i_t_y _S_y_n_t_a_x _G_u_i_d_e_l_i_n_e_s

CCOOPPYYRRIIGGHHTT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 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 .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .



IEEE/The Open Group                  2017                              HEAD(1)
