Unix Features, POSIX and Single UNIX specification, Understanding the man

configuration

SudhaRani.SComputer Science & Engineering

Features of UNIX

Multiuser capability and background processing

Multitasking capabilityCommunicationSecurity, SimplePortability

Features of UNIXTime sharingCommand interpreterHierarchical file systemSimple command structureBuilding-Block approachUNIX toolkitPattern Matching

Features of UNIX

File security and protectionDOS-UNIX interfaceSystem administration and job accounting

Tools and utilitiesShell and shell programming

Features of UNIXOnline documentationAvailability of 4GL and RDBMSLibrary of application packagesText processingGraphicsOperational units

POSIX and Single UNIX Specification

POSIX (Portable Operating System Interface for computer Environments) refers to operating system based on UNIX.

Developed at IEEE.Refers to Operating System based on UNIX.POSIX.1 - C application programming interface,

the system calls

POSIX and Single UNIX Specification

POSIX.2 - deals with the Shell and Utilities.POSIX 4 - thread management. Unification of two standards (POSIX.1 & POSIX.2)

known as Single UNIX Specification(SUSV3). “Write once, adopt everywhere” once the software has been developed on any POSIX, it can be easily ported to another POSIX UNIX machine with lesser modifications.

Understanding the man configuration

The UNIX man pages (man is short for manual ) cover every command available.

To search for a man page, enter man followed by the name of the command to find .

For exampleman ls

Man searches the manuals starting from section 1. Depending on the UNIX flavour we need to use the prefix –s option to the section number

man 4 passwd //passwd alos occurs in section 4man –s4 passwd // solaris uses the –s option

Understanding the man configurationThis displays the documentation for a

configuration file named /etc/passwd from section 4.

There’s also an entry for passwd in section 1 using man passwd (without the section number)

man passwd

Understanding the man page

A man page is divided into a number of compulsory and optional sections. It holds NAME,SYNOPSIS,DESCRIPTION.

NAME – one line introduction to the commandWc – displays a count of lines, words and characters in a file

Understanding the man page

SYNOPSIS – syntax used by the commandWc [-c | -m| -C ] [-lw] [file ….]Where - c is count bytes-m and –C is count characters-l count lines-w count words

DESCRIPTION – provides a detailed descriptionDescription about wc in detail

Using man to Understand man

man man is used to view its own documentation. Viewing man pages with man

The variable PAGER controls the pager man uses and if you set it to less then man will use less as its pager. PAGER = less; export PAGERMan wc

To evaluate the value of PAGER, use the command echo $PAGER. This valid only for the current session.

Further help with man

The POSIX specification requires man to support only one option –k

It searches a summary database and prints a one line description of the command.

To know what awk does, use man command$ man –k awk