LPI Linux Certification in a Nutshell (13 page)

man

man [
options
] [
section
]
name

Format and display system manual pages from
section
on the topic of
name
. If
section
is omitted, the first manpage
found is displayed.

View a manpage for
mkfifo
:

$
man mkfifo
...

Results for the first manpage found are scrolled on the
screen.

Determine what manpages are available for
mkfifo
:

$
man -wa mkfifo
/usr/share/man/man1/mkfifo.1
/usr/share/man/man3/mkfifo.3

This shows that two manpages are available, one in section 1
(
mkfifo.1
) of the manual and another in section
3 (
mkfifo.3
). See the next section for a
description of manpage sections.

Display the
mkfifo
manpage from manual
section 3:

$
man 3 mkfifo

Manpages are grouped into
sections
, and there are times
when you should know the appropriate section in which to search for
an item. For example, if you were interested in the
mkfifo
C-language
function rather than the
command, you must tell the
man
program to
search the section on library functions (in this case, section 3,
Linux Programmer’s Manual
):

$
man 3 mkfifo

An alternative would be to have the
man
program search all manual sections:

$
man -a mkfifo

The first example returns the
mkfifo(3)
manpage regarding the library function. The second returns pages for
both the command and the function. In this case, the pages are
delivered separately; terminating the pager on the first manpage
with Ctrl-C causes the second to be displayed.

Manual sections are detailed in
Table 6-3
.

The order in which
man
searches the
sections for manpages is controlled by the
MANSECT
environment variable.
MANSECT
contains a colon-separated list of
section numbers. If it is not set,
man
(as of
version 1.5k) behaves as if it were set to
1:8:2:3:4:5:6:7:9:tcl:n:l:p:o
.

Most manpages are presented in a concise format with
information grouped under well-known standard headings such as those
shown in
Table 6-4
. Other manpage
headings depend on the context of the individual manpage.

System manpages are stored mostly in
/usr/share/man
, but may exist in other places
as well. At any time, the manual pages available to the
man
command are contained within directories
configured in your
man
configuration file,
/etc/man.config
. This file
contains directives to the
man
, telling it
where to search for pages (the
MANPATH
directive), the paging program to
use (
PAGER
), and many others.
This file essentially controls how
man
works on
your system. To observe this, use the debug
(
-d
) option to
man
to
watch as it constructs a
manpath
(a directory search list)
and prepares to display your selection:

$
man -d mkfifo

cat

cut
options
[
files
]

Concatenate files and print on the standard output. Cat
is often used as the first command in a text stream, as it simply
sends the contents of a file (or multiple files) to the standard
output.

Send the contents of the file
/etc/passwd
to the file
/tmp/passwd
:

$
cat /etc/passwd > /tmp/passwd

cut

cut
options
[
files
]

Cut out (that is, print) selected columns or fields from
one or more
files
. The source file is not
changed. This is useful if you need quick access to a vertical
slice of a file. By default, the slices are delimited by
a Tab character.

Show usernames (in the first colon-delimited field) from
/etc/passwd
:

$
cut -d: -f1 /etc/passwd

expand

expand [
options
] [
files
]

Convert Tabs to spaces. Sometimes the use of
Tab characters can make output that is attractive on one
output device look bad on another. This command eliminates Tabs and
replaces them with the equivalent number of spaces. By default, Tabs
are assumed to be eight spaces apart.

fmt

fmt [
options
] [
files
]

Format text to a specified width by filling lines and
removing
newline characters. Multiple
files
from the command line are
concatenated.

head

head [
options
] [
files
]

Print the first few lines of one or more files (the
“head” of the file or files). When more than one file is specified, a
header is printed at the beginning of each file, and each is listed in
succession.

join

join [
options
]
file1 file2

Print a line for each pair of input lines, one each from
file1
and
file2
,
that have identical
join fields
. This function could be
thought of as a very simple database table join, where the two files
share a common index just as two tables in a database would.

Suppose
file1
contains the
following:

1 one
2 two
3 three

and
file2
contains:

1 11
2 22
3 33

Issuing the command:

$
join -j 1 file1 file2

yields the following output:

1 one 11
2 two 22
3 three 33