LPI Linux Certification in a Nutshell (14 page)

nl

nl [
options
] [
files
]

Number the lines of
files
,
which are concatenated in the output. This command is used for
numbering lines in the body of text, including special header and
footer options normally excluded from the line numbering. The
numbering is done for each
logical page
, which is defined as
having a header, a body, and a footer. These are delimited by the
special strings
\:\:\:
,
\:\:
, and
\:
, respectively.

Styles can be in these forms:

Suppose file
file1
contains the following
text:

\:\:\:
header
\:\:
line1
line2
line3
\:
footer
\:\:\:
header
\:\:
line1
line2
line3
\:
footer

If the following command is given:

$
nl -h a file1

the output would yield numbered headers and body lines but no
numbering on footer lines. Each new header represents the beginning of
a new logical page and thus a restart of the numbering
sequence:

1  header
2  line1
3  line2
4  line3
footer
1  header
2  line1
3  line2
4  line3
footer

od

od [
options
] [
files
]

Dump files in octal and other formats. This program
prints a listing of a file’s contents in a variety of formats. It is
often used to examine the byte codes of binary files but can be used
on any file or input stream. Each line of output consists of an octal
byte offset from the start of the file followed by a series of tokens
indicating the contents of the file. Depending on the options
specified, these tokens can be ASCII, decimal, hexadecimal, or octal
representations of the contents.

Typical types include:

If
file1
contains:

a1\n
A1\n

where
\n
stands for the
newline character, the
od
command specifying
named characters yields the following output:

$
od -t a file1
00000000   a   1  nl   A   1  nl
00000006

A slight nuance is the ASCII character mode. This
od
command specifying named characters yields the
following output with backslash-escaped characters rather than named
characters:

$
od -t c file1
00000000   a   1  \n   A   1  \n
00000006

With numeric output formats, you can instruct
od
on how many bytes to use in interpreting each
number in the data. To do this, follow the type specification by a
decimal integer. This
od
command specifying
single-byte hex results yields the following output:

$
od -t x1 file1
00000000  61 31 0a 41 31 0a
00000006

Doing the same thing in octal notation yields:

$
od -t o1 file1
00000000  141 061 012 101 061 012
00000006

If you examine an ASCII chart with hex and octal
representations, you’ll see that these results match those
tables.

paste

paste [
options
] [
files
]

Paste together corresponding lines of one or more
files
into vertical columns. Similar in
function to the
join
command, but simpler in
scope.

For the following three examples,
file1
contains:

1
2
3

and
file2
contains:

A
B
C

A simple
paste
creates columns from each
file in standard output:

$
paste file1 file2
1    A
2    B
3    C

The column separator option yields columns separated by the
specified character:

$
paste -d'@' file1 file2
1@A
2@B
3@C

The single-line option (
-s
) yields a line
for each file:

$
paste -s file1 file2
1    2    3
A    B    C

pr

pr [
options
] [
file
]

Convert a text file into a paginated, columnar version,
with headers and page fills. This command is convenient for yielding
nice output, such as for a line printer from raw, uninteresting text
files. The header will consist of the date and time, the filename, and
a page number.

sort

sort [
options
] [
files
]

Write input to
stdout
(standard
out), sorted alphabetically.

Sort all processes on the system by resident size (
RSS
in
ps
):

$
ps aux | sort -k 6 -n
USER   PID  %CPU %MEM VSZ   RSS  TTY   STAT START  TIME   COMMAND
root   2    0.0  0.0  0     0    ?     SW   Feb08   0:00  [keventd]
root   3    0.0  0.0  0     0    ?     SWN  Feb08   0:00  [ksoftirqd_CPU0]
root   4    0.0  0.0  0     0    ?     SW   Feb08   0:01  [kswapd]
root   5    0.0  0.0  0     0    ?     SW   Feb08   0:00  [bdflush]
root   6    0.0  0.0  0     0    ?     SW   Feb08   0:00  [kupdated]
root   7    0.0  0.0  0     0    ?     SW   Feb08   0:00  [kjournald]
root   520  0.0  0.3  1340  392  tty0  S    Feb08   0:00  /sbin/mingetty tt
root   335  0.0  0.3  1360  436  ?     S    Feb08   0:00  klogd -x
root   1    0.0  0.3  1372  480  ?     S    Feb08   0:18  init
daemon 468  0.0  0.3  1404  492  ?     S    Feb08   0:00  /usr/sbin/atd
root   330  0.0  0.4  1424  560  ?     S    Feb08   0:01  syslogd -m 0
root   454  0.0  0.4  1540  600  ?     S    Feb08   0:01  crond
root   3130 0.0  0.5  2584  664  pts/0 R    13:24   0:00  ps aux
root   402  0.0  0.6  2096  856  ?     S    Feb08   0:00  xinetd -stayalive
root   385  0.0  0.9  2624  1244 ?     S    Feb08   0:00  /usr/sbin/sshd
root   530  0.0  0.9  2248  1244 pts/0 S    Feb08   0:01  -bash
root   3131 0.0  0.9  2248  1244 pts/0 R    13:24   0:00  -bash
root   420  0.0  1.3  4620  1648 ?     S    Feb08   0:51  sendmail: accepti
root   529  0.0  1.5  3624  1976 ?     S    Feb08   0:06  /usr/sbin/sshd

split

split [
option
] [
infile
] [
outfile
]

Split
infile
into a specified
number of line groups, with output going into a succession of files,
outfile
aa
,
outfile
ab
, and so on (the default is
xaa
,
xab
, etc.). The
infile
remains unchanged. This command is
handy if you have a very long text file that needs to be reduced to a
succession of smaller files. This was often done to email large files
in smaller chunks, because at one time it was considered bad practice
to a send a single large email message.

Suppose
file1
contains:

1  one
2  two
3  three
4  four
5  five
6  six

Then the command:

$
split -2 file1 splitout_

yields as output three new files,
splitout_aa
,
splitout_ab
,
and
splitout_ac
.

The file
splitout_aa
contains:

1  one
2  two

splitout_ab
contains:

3  three
4  four

and
splitout_ac
contains:

5  five
6  six

tac

tac [
file
]

This command is named as an opposite for the
cat
command, which simply prints text files to
standard output. In this case,
tac
prints the
text files to standard output with lines in reverse order.

Suppose
file1
contains:

1  one
2  two
3  three

Then the command:

$
tac file1

yields as output:

3  three
2  two
1  one

tail

tail [
options
] [
files
]

Print the last few lines of one or more
files
(the “tail” 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.