Advanced Programming in the UNIX® Environment

ptg10805159

6 UNIX System Overview Chapter 1

Some UNIX systems further divide the manual pages within a given section, using an

uppercase letter.For example, all the standardinput/output(I/O)functions in AT&T [1990e]

areindicated as being in Section 3S, as infopen(3S).Other systems have replaced the

numeric sections with alphabetic ones, such as C for commands.

Today,most manuals aredistributed in electronic form. If your manuals areonline,

the way to see the manual pages for thelscommand would be something like

man 1 ls

or

man -s1 ls

Figure1.3 is a program that just prints the name of every file in a directory,and

nothing else. If the source file is namedmyls.c, we compile it into the defaulta.out

executable file by running

cc myls.c

Historically,cc( 1 )is the C compiler.Onsystems with the GNU C compilation system, the C

compiler isgcc( 1 ).Here,ccis usually linked togcc.

Some sample output is

$./a.out /dev

.

..

cdrom

stderr

stdout

stdin

fd

sda4

sda3

sda2

sda1

sda

tty2

tty1

console

tty

zero

null

many morelines that aren’tshown

mem

$./a.out /etc/ssl/private

can’t open /etc/ssl/private: Permission denied

$./a.out /dev/tty

can’t open /dev/tty: Not a directory

Throughout this text, we’ll show commands that we run and the resulting output in this

fashion: Characters that we type areshown in this font,whereas output from

programs is shownlike this.If we need to add comments to this output, we’ll show

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