head

display first part of file 

Command

SYNOPSIS

head [-bcklmn num] [-U[[[c][lb8oa]][p[lb8oa]]]] [file ...]

head [-num] [-U[[[c][lb8oa]][p[lb8oa]]]] [file ...]

DESCRIPTION

By default, head displays the first 10 lines of each text file given on the command line. If you do not specify file, head reads the standard input.

Besides normal ASCII text files, head also works on UTF-8 files and 16-bit wide Unicode files. Such files normally begin with a multiple-byte marker indicating whether the file's contents are Unicode big-endian, Unicode little-endian, or UTF-8. Such files are detected automatically by head; however, when the multiple-byte marker is missing you can use the -U option or the TK_STDIO_DEFAULT_INPUT_FORMAT/TK_STDIO_DEFAULT_OUTPUT_FORMAT environment variables to force any file to be treated as a Unicode or UTF-8 file.

Normally, head's output format defaults to the format of the first file it displays unless the -U option or the TK_STDIO_DEFAULT_OUTPUT_FORMAT environment variable is used to override the output format. For more details on this and other Unicode-related file handling issues see the unicode reference page.

Options

-b num 

displays the first num x 512 characters of each file. With single byte characters, this is the first num blocks (a block is 512 bytes) of the file.

-c num 

displays the first num characters of each file.

-k num 

displays the first num x 1024 characters of each file. With single byte characters, this is the first num kilobytes of the file.

-l num 

displays the first num lines of each file.

-m num 

displays the first num x 1048576 (1024 x 1024) characters of each file. With single byte characters, this is the first num megabytes of the file.

-n num 

displays the first num lines of each file.

-U[[[c][lb8oa]][p[lb8oa]]] 

specifies the input format of any file missing the initial multiple-byte marker, the output format produced, or both.

When c is specified, the specifiers that follow it apply to the input consumed.

When p is specified, the specifiers that follow it apply to the output produced.

When neither c nor p are specified, the remaining -U specifiers apply to the input consumed.

When both c and p are specified, the remaining -U arguments apply to both input and output.

The remaining specifiers indicate the format of the characters read from input or written to output (as determined by c and p): 

l     little-endian 16-bit wide characters
b     big-endian 16-bit wide characters
8     UTF-8 characters
a     ASCII characters from the ANSI code page
o     ASCII characters from the OEM code page

When multiple format specifiers can be associated with either c or p, the last appropriate one given on the command for each of c and p is used. For example: 

-Ucoapl8

is the same as: 

-Ucap8

When a p specifier is given without a c specifier and format specifiers are given before the p specifier, those format specifiers apply to the input. For example: 

-Uopl

is the same as: 

-Ucopl

When c or p is specified with no format specifies, little endian 16-bit wide characters are used by default for either input or output, as appropriate.

As an alternative to specifying formats for both input and output with the same -U option, you can specify the -U option multiple times. For example, the following are identical: 

-Uca -Upb
-Ucapb

Note:

The -U specifiers are actually case-insensitive. For example, the following are all identical in their behavior: 

-Ucl
-UcL
-UCl
-UCL

-num 

displays the first num lines of each file.

ENVIRONMENT VARIABLES

TK_STDIO_DEFAULT_INPUT_FORMAT 

Sets the default input format for files that don't have the initial multibyte marker. The value must be one of those listed in the File Character Formats section of the unicode reference page.

TK_STDIO_DEFAULT_OUTPUT_FORMAT 

Sets the default output format. Normally the format of the first file read is used as the default output format. The value must be one of those listed in the File Character Formats section of the unicode reference page.

DIAGNOSTICS

Possible exit status values are:

0 

Successful completion.

1 

Failure due to any of the following:

— cannot open an input file
— read error on the standard input
— write error on the standard output
2 

Failure due to any of the following:

— unknown command line option
— missing or invalid num in a -n option

Badly formed line/byte count "num" 

The value num, following a -b, -c, -k, -l, -m, or -n option was not a valid number.

PORTABILITY

POSIX.2. x/OPEN Portability Guide 4.0. Windows 8.1. Windows Server 2012 R2. Windows 10. Windows Server 2016. Windows Server 2019. Windows 11. Windows Server 2022.

The POSIX.2 standard only includes the -n num and -num options though it considers the latter obsolete.

AVAILABILITY

PTC MKS Toolkit for Power Users
PTC MKS Toolkit for System Administrators
PTC MKS Toolkit for Developers
PTC MKS Toolkit for Interoperability
PTC MKS Toolkit for Professional Developers
PTC MKS Toolkit for Professional Developers 64-Bit Edition
PTC MKS Toolkit for Enterprise Developers
PTC MKS Toolkit for Enterprise Developers 64-Bit Edition

SEE ALSO

Commands:
cat, pg, sed, tail

PTC MKS Toolkit 10.4 Documentation Build 39.