Head (Unix)
Encyclopedia
head is a program
on Unix
and Unix-like
systems used to display the first few lines of a text file
or piped data. The command syntax
is:
head [options] <file_name>
By default, head will print the first 10 lines of its input to the standard output. The number of lines printed may be changed with a command line option. The following example shows the first 20 lines of filename:
head -n 20 filename
This displays the first 5 lines of all files starting with foo:
head -n 5 foo*
Some versions omit the n and just let you say -5.
do this job:
sed 5q foo
This says to print every line (implicit), and quit after the fifth.
Computer program
A computer program is a sequence of instructions written to perform a specified task with a computer. A computer requires programs to function, typically executing the program's instructions in a central processor. The program has an executable form that the computer can use directly to execute...
on Unix
Unix
Unix is a multitasking, multi-user computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs, including Ken Thompson, Dennis Ritchie, Brian Kernighan, Douglas McIlroy, and Joe Ossanna...
and Unix-like
Unix-like
A Unix-like operating system is one that behaves in a manner similar to a Unix system, while not necessarily conforming to or being certified to any version of the Single UNIX Specification....
systems used to display the first few lines of a text file
Computer file
A computer file is a block of arbitrary information, or resource for storing information, which is available to a computer program and is usually based on some kind of durable storage. A file is durable in the sense that it remains available for programs to use after the current program has finished...
or piped data. The command syntax
Syntax
In linguistics, syntax is the study of the principles and rules for constructing phrases and sentences in natural languages....
is:
head [options] <file_name>
By default, head will print the first 10 lines of its input to the standard output. The number of lines printed may be changed with a command line option. The following example shows the first 20 lines of filename:
head -n 20 filename
This displays the first 5 lines of all files starting with foo:
head -n 5 foo*
Some versions omit the n and just let you say -5.
Other
Many early versions of Unix did not have this command, and so documentation and books had sedSed
sed is a Unix utility that parses text and implements a programming language which can apply transformations to such text. It reads input line by line , applying the operation which has been specified via the command line , and then outputs the line. It was developed from 1973 to 1974 as a Unix...
do this job:
sed 5q foo
This says to print every line (implicit), and quit after the fifth.
External links
- head manual page from GNUGNUGNU is a Unix-like computer operating system developed by the GNU project, ultimately aiming to be a "complete Unix-compatible software system"...
coreutils. - FreeBSD documentation for head