# head

## PROLOG



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


## NAME



           head — copy the first part of files
    


## SYNOPSIS



           head **[** -n _number_**] [**_file_...**]**
    


## DESCRIPTION



           The _head_ 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
           **-n** _number_ option. The option-argument _number_ shall be counted in
           units of lines.
    


## OPTIONS



           The _head_ utility shall conform to the Base Definitions volume of
           POSIX.1‐2017, _Section 12.2_ , _Utility Syntax Guidelines_.
    
           The following option shall be supported:
    
           **-n** _number_ The first _number_ lines of each input file shall be
                     copied to standard output. The application shall ensure
                     that the _number_ option-argument is a positive decimal
                     integer.
    
           When a file contains less than _number_ lines, it shall be copied to
           standard output in its entirety. This shall not be an error.
    
           If no options are specified, _head_ shall act as if **-n 10** had been
           specified.
    


## OPERANDS



           The following operand shall be supported:
    
           _file_      A pathname of an input file. If no _file_ operands are
                     specified, the standard input shall be used.
    


## STDIN



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


## INPUT FILES



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


## ENVIRONMENT VARIABLES



           The following environment variables shall affect the execution of
           _head_ :
    
           _LANG_      Provide a default value for the internationalization
                     variables that are unset or null. (See the Base
                     Definitions volume of POSIX.1‐2017, _Section 8.2_ ,
                     _Internationalization Variables_ for the precedence of
                     internationalization variables used to determine the
                     values of locale categories.)
    
           _LC_ALL_    If set to a non-empty string value, override the values
                     of all the other internationalization variables.
    
           _LC_CTYPE_  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).
    
           _LC_MESSAGES_
                     Determine the locale that should be used to affect the
                     format and contents of diagnostic messages written to
                     standard error.
    
           _NLSPATH_   Determine the location of message catalogs for the
                     processing of _LC_MESSAGES_.
    


## ASYNCHRONOUS EVENTS



           Default.
    


## STDOUT



           The standard output shall contain designated portions of the input
           files.
    
           If multiple _file_ operands are specified, _head_ shall precede the
           output for each with the header:
    
               "\n==> %s <==\n", <_pathname_ >
    
           except that the first header written shall not include the initial
           <newline>.
    


## STDERR



           The standard error shall be used only for diagnostic messages.
    


## OUTPUT FILES



           None.
    


## EXTENDED DESCRIPTION



           None.
    


## EXIT STATUS



           The following exit values shall be returned:
    
            0    Successful completion.
    
           >0    An error occurred.
    


## CONSEQUENCES OF ERRORS



           Default.
    
           _The following sections are informative._
    


## APPLICATION USAGE



           When using _head_ 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.
    


## EXAMPLES



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


## RATIONALE



           Although it is possible to simulate _head_ with _sed_ 10q for a single
           file, the standard developers decided that the popularity of _head_
           on historical BSD systems warranted its inclusion alongside _tail_.
    
           POSIX.1‐2008 version of _head_ follows the Utility Syntax
           Guidelines. The **-n** option was added to this new interface so that
           _head_ and _tail_ would be more logically related. Earlier versions of
           this standard allowed a **-number** option. This form is no longer
           specified by POSIX.1‐2008 but may be present in some
           implementations.
    
           There is no **-c** option (as there is in _tail_) because it is not
           historical practice and because other utilities in this volume of
           POSIX.1‐2017 provide similar functionality.
    


## FUTURE DIRECTIONS



           None.
    


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