Linux+ Chapter1

Front 1

bash (descr.)

bsh (descr.)

Back 1

bash (descr.)
Bourne Again Shell
base on earlier Bourne shell but extended
The most commong default shell

bsh (descr.)
Bourne shell
bsh is base for bash
not often used in linux

Front 2

tcsh (descr.)

csh (descr.)

Back 2

tcsh (descr.)
based on C shell (csh)
no major Linux distro use it

csh (descr.)
original C shell
not used on Linux

Front 3

ksh (descr.)

zsh (descr.)

Back 3

ksh
The Korn shell
Combines Bourne shell and C shell

zsh
The Z shell
incorporates features from earlier shells and adding still more

Front 4

What is the file /bin/sh

Back 4

is a symbolic link to the system's default shell
normaly this is /bin/bash for Linux

Front 5

for the most part, Linux cmd are ____________________
a few commands are _______ to the shell

Back 5

for the most part, Linux cmd are EXTERNAL - separate programs from the shell. A few commands are INTERNAL to the shell

Front 6

change the working directory

Back 6

cd
cd /home/sally

Front 7

what ~ stands for

Back 7

~ is a shortcut it stands for your home directory
cd ~
will have the same effect as
cd /home/sally

Front 8

display a line of text cmd
execute a program cmd

Back 8

echo Hello
exec myprog
in most cases executing a program is better done by typing the name of the program

Front 9

"time" cmd

Back 9

time cmd
times how long subsequent cmd takes t oexecutre
time pwd - tells you how long the system took to execute
Three times are displayed: total executin time
user CPU time
system CPU time

Front 10

"set" cmd

Back 10

set
in its most basic form set displays a wide variety of options relating to bash

Front 11

PATH enviorment varialbe

Back 11

When you type a cmd that is not recognized by the sjell as one of its internal cmds, the shell checks its path to fina a program by that name to execute it.
Define by the PATH enviroment variable.
You can adjust by changing the PATH enviorment

Front 12

Warning for PATH

Back 12

root’s path should never include the current directory
./.
Placing this directory in root’s path makes it possible for a local miscreant
to trick root into running replacements for common programs, such
as ls, by having root change into a directory with such a program. Indeed,
omitting the current directory from ordinary user paths is also generally a
good idea. If this directory must be part of the ordinary user path, it should
appear at the end of the path so that the standard programs take precedence
over any replacement programs in the current directory

Front 13

command completion

Back 13

Type part of a command
or (as an option to a command) a filename, and then press the Tab key. The shell tries to fill
in the rest of the command or the filename.

Front 14

history

Back 14

Another helpful shell shortcut is the history. The history keeps a record of every command you type (stored in ~/.bash_history in the case of bash).

Front 15

open termina in Ubuntu

Back 15

Ctrl + Alt + T

Dash -> More Apps -> 'See More Results' -> Terminal

Dash -> More Apps -> Accessories -> Terminal

Front 16

xterm (cmd)

Back 16

will launch the xterm shell

Front 17

touch <file name>

clear (cmd)

Back 17

create a brand new blank file

clears terminal window

Front 18

shutdown linux cmd
and
how to reboot?

Back 18

sudo shutdown -h now
sudo shutdown -h 0
sudo shutdown -h 18:45 "Server is going down for maintenance"

Please note that you can also use halt or poweroff or reboot command for stopping and restarting the system:
$ sudo halt
$ sudo poweroff
How do I reboot computer?
sudo shutdown -r 0
sudo reboot

Front 19

using command history

Back 19

CTRL + R - backward search
CTRL + S - forward search
CTRL + G - terminates search

Front 20

move within the command line

Back 20

CTRL + A/CTRL + E
moves cursor to the start or end of the line
<- and -> move the cursor a character at a time same as (CTRL+B and CTRL+F)
CTRL+K - del. all text from current cursor to the end of line

Front 21

invoka an editor

Back 21

lanch full editor by pressing
CTRL + X followed by CTRL + E
Bash shell attempts to launch the editor defined by the $FCEDIT or $EDITOR

Front 22

delete a file <cmd>

Back 22

rm -f -r {file-name}

■-f: Forcefully remove file
■-r: Remove the contents of directories recursively

Front 23

main user config file for bash

main global config file for bash

Back 23

main user config file for bash
~/.bashrc
~/.profile
main global config file for
bash
/etc/bash.bashrc
/etc/profile

Front 24

cmd to learn about man itself

Back 24

man man

Front 25

for instance, passwd has entries
under both section 1 and section 5. In most cases, man returns the entry in the lowest-numbered
section; but you can force the issue by preceding the keyword by the section number.What cmd does that

Back 25

man 5 passwd

Front 26

Some programs have moved away from man pages to info pages. The basic purpose of
info pages is the same as that for man pages, but info pages use a hypertext format

Back 26

info info

Front 27

Redirecting Input and Output

Back 27

echo $NNTPSERVER > nntpserver.txt

Front 28

What creates a new file containing standard output. If the specified file
exists, it’s overwritten.

Back 28

>

Front 29

Appends standard output to the existing file. If the specified file
doesn’t exist, it’s created.

Back 29

>>

Front 30

Creates a new file containing standard error. If the specified file
exists, it’s overwritten.

Back 30

2>

Front 31

Appends standard error to the existing file. If the specified file
doesn’t exist, it’s created.

Back 31

2>>

Front 32

Creates a new file containing both standard output and standard
error. If the specified file exists, it’s overwritten.

Back 32

&>

Front 33

Sends the contents of the specified file to be used as standard
input.

Back 33

<

Front 34

Accepts text on the following lines as standard input.

Back 34

<<

Front 35

Causes the specified file to be used for both standard input and
standard output.

Back 35

<>

Front 36

what is /dev/null

Back 36

This file is a device that’s connected to nothing; it’s used when you
want to get rid of data.
For instance, if the whine program is generating too
many error messages, you can type whine 2> /dev/null to run it and discard
its error messages.

Front 37

tee command

Back 37

his command splits standard input so that
it’s displayed on standard output and on as many files as you specify.

someprog | tee output.txt

Front 38

data pipes (a.k.a. pipelines)

Back 38

A pipe redirects the first program’s
standard output to the second program’s standard input and is denoted by a vertical bar (|):
$ first | second

Front 39

general rule for files ending with ~

Back 39

file ending with ~ denote backups files created by certain text editors

Front 40

xargs [options] [command [initial-arguments]]

general usage

Back 40

xargs cmd builds a comand from its standard input.

command - the cmd you want to executre
initial-arguments - list of argumentsyou want to pass to the cmd
options - xargs options

Front 41

using xargs delete all file that end with ~

Back 41

$ find ./ -name “*~” | xargs rm
The first part of this command (find ./ -name “*~”) finds all the files in the current
directory (./) or its subdirectories with a name that ends in a tilde (*~). This list is then
piped to xargs, which adds each one to its own rm command.

Front 42

what is backtick (`)

Back 42

Text within backticks is treated as a separate command whose results are substituted on the
command line.
$ rm `find ./ -name “*~”`

Front 43

mac categories

Back 43

1 Executable programs and shell commands
2 System calls provided by the kernel
3 Library calls provided by program libraries
4 Device files (usually stored in /dev)
5 File formats
6 Games
7 Miscellaneous (macro packages, conventions, and so on)
8 System administration commands (programs run mostly or exclusively
by root)
9 Kernel routines

Front 44

uses for ` (backtick)

Back 44

the text within backticks is treated as a separete cmd whose results are substituted on the cmd line

rm `fin ./ -name "*~"` - deletes all files ending with ~

Front 45

cat (cmd)

Back 45

links together an arbitrary number of files end to end and send the result to standard output

cat first.txt second.txt > combined.txt

Front 46

Display line ends cmd

Number lines cmd

Back 46

cat -E or
cat --show-ends
The result is dollar sign at the end of each file

cat -n
cat --number
Adds line numbers to the beginning of every line even empty

Front 47

Number lines but not blank

Back 47

cat -b
car --number-nonblank
adds a line numbers but it numbers only lines that contain text

Front 48

cmd option that compresses groups of blank lines down to a single blank line

Back 48

cat -s
cat --squeeze-blank

Front 49

cmd option to display special character

cmd option that display most control and other special characters using carat (^) and M- notations

Back 49

cat .. -T
cat .. --show-tabs

cat .. -v
cat .. show-tabs

Front 50

join cmd (expl)

Back 50

join command combines two files by matching the contents of specified fields within
the files. Fields are typically space-separated entries on a line, although you can specify
another character as the field separator with the -t char option, where char is the character
you want to use. You can cause join to ignore case when performing comparisons by
using the -i option.

Front 51

join cmd example

Back 51

ls1.txt
555-2397 Beckett, Barry
555-5116 Carter, Gertrude
ls2.txt
555-2397 unlisted
555-5116 listed

$ join listing1.1.txt listing1.2.txt
555-2397 Beckett, Barry unlisted
555-5116 Carter, Gertrude listed

Front 52

paste cmd example

Back 52

ls1.txt
555-2397 Beckett, Barry
555-5116 Carter, Gertrude
ls2.txt
555-2397 unlisted
555-5116 listed

$ paste listing1.1.txt listing1.2.txt
555-2397 Beckett, Barry 555-2397 unlisted
555-5116 Carter, Gertrude 555-5116 listed

Front 53

paste (cmd)

Back 53

paste command merges files line by line, separating the lines from each file with tabs

paste listing1.1.txt listing1.2.txt

Front 54

Converting Tabs to Spaces (cmd)

Back 54

expand

By default, expand assumes a tab stop every eight characters. You can change this spacing
with the -t num or --tabs=num option, where num is the tab spacing value.

Front 55

Displaying Files in Octal (cmd)

Back 55

od - octal dump

Displaying Files in Octal

od listing1.2.txt
0000000 032465 026465 031462 033471 072440 066156 071551 062564

Front 56

Sorting Files (cmd)

Back 56

sort

-f or --ignore-case
-M or --month-sort - sort by three-letter month abbr
-n or --numeric-sort
-k field or --key=field option. (The field can be two numbered fields separated by commas, to sort on multiple fields.)
$ sort -k 3 listing1.1.txt

Front 57

Breaking a File into Pieces (cmd)

Back 57

split

Split by bytes -b size or --bytes=size This option can have the usually undesirable consequence of splitting the file mid-line.
Split by bytes in line-sized chunks -C=size or --line-bytes=size option.
Split by number of lines The -l lines or --lines=lines

Front 58

Translating Characters (cmd)

Back 58

tr
You specify the characters you want replaced in a group (SET1) and the characters with
which you want them to be replaced as a second group (SET2). Each character in SET1 is
replaced with the one at the equivalent position in SET2
$ tr BCJ bc < listing1.1.txt

Front 59

Converting Spaces to Tabs (cmd)

Back 59

unexpand command is the logical opposite of expand; it converts multiple spaces to
tabs.

Front 60

Deleting Duplicate Lines (cmd)

Back 60

uniq

$ sort shakespeare.txt | uniq

Front 61

Reformatting Paragraphs

Back 61

fmt
If you want to clean up the file a bit, though, you can do so with fmt. If called with no options the program attempts to clean up paragraphs, which it assumes are delimited by two or more blank lines or by changes in indentation

Front 62

Numbering Lines
Body numbering
Header and Footer numbering

Back 62

nl
Body numbering style -b style or --body-numbering=style
Header and footer numbering style
-h style or --header-numbering=style
-f style or --footer-numbering=style

Front 63

Numbering Lines Number format (cmd)

Back 63

Page separator - Some numbering schemes reset the line numbers for each page
Line-number options for new pages -p or --no-renumber
Number format -n format or --numberformat=
format option, where format is ln (left justified, no leading zeros), rn (right justified,
no leading zeros), or rz (right justified with leading zeros)

Front 64

Numbering Lines Number only non-blank lines (cmd)

Back 64

The default behavior is to number lines that aren’t empty.
This corresponds to a style of t.

Front 65

Numbering Lines Number all lines, Number no lines (cmd)

Back 65

Number all lines
specify a style of a
Number no lines
specify a style of n

Front 66

Numbering Lines Number lines matching a regular expression (cmd)

Back 66

A style of pREGEXP numbers only those
lines that match the regular expression REGEXP.

Front 67

suppose you’ve created a script, buggy, but you find that it’s not working
as you expect. When you run it, you get error messages that refer to line numbers, so you
want to create a version of the script with lines that are numbered for easy reference. What cmd you use?

Back 67

$ nl -b a buggy > numbered-buggy.txt

Front 68

Preparing a File for Printing (cmd)

Back 68

pr

If you want to print a plain-text file, you may want to prepare it with headers, footers, page
breaks, and so on. The pr command was designed to do this. In its most basic form, you
pass the command a file:
$ pr myfile.txt

Front 69

pr Generate multi-column output (cmd option)

Back 69

Passing the -numcols or --columns=numcols option creates
output with numcols columns. Note that pr doesn’t reformat text; if lines are too long,
they’re truncated or run over onto multiple columns.

Front 70

pr Generate double-spaced output (cmd option)

Back 70

-d or --double-space option causes double-spaced
output from a single-spaced file.

Front 71

pr Use form feeds (cmd option)

Back 71

pr separates pages by using a fixed number of blank lines If you have
problems with this issue, you can pass the -F, -f, or --form-feed option, which causes pr
to output a form-feed character between pages.

Front 72

pr Set page length (cmd option)
+ Set the header text
+ Set left margin and page width

Back 72

The -l lines or --length=lines option sets the length of the page in lines.
The -h text or --header=text
The -o chars or --indent=chars option sets the left margin
to chars characters

Front 73

example of pr in action, consider printing a double-spaced and numbered version
of a configuration file (say, /etc/profile) for your reference

Back 73

cat -n /etc/profile | pr -d | lpr

Front 74

Viewing the Starts of Files

Back 74

head
Specify the number of bytes The -c num or --bytes=num option tells head to display num
bytes from the file rather than the default 10 lines.
Specify the number of lines You can change the number of lines displayed with the -n
num or --lines=num option.

Front 75

Viewing the Ends of Files

Back 75

tail

-c/--bytes and -n/--lines options to change the amount of data displayed,
just as with head

Front 76

tail Track a file (option)
!!!

Back 76

-f or --follow option tells tail to keep the file open and to display new
lines as they’re added. This feature is helpful for tracking log files because it enables you to
see changes as they’re added to the file.

Front 77

tail Stop tracking on program termination (option)

Back 77

--pid=pid option tells tail to terminate
tracking (as initiated by -f or --follow) once the process with a process ID (PID) of pid
terminates

Front 78

Paging Through Files (option)

Back 78

less - less filename

Front 79

less usage options

Back 79

Pressing the spacebar moves forward through t NN he file a screen at a time.
NN Pressing Esc followed by V moves backward through the file a screen at a time.
NN The Up and Down arrow keys move up or down through the file a line at a time.
NN You can search the file’s contents by pressing the slash (/) key followed by the search
term. For instance, typing /portable
You can search backward in the file by using the question mark (?) key rather than the
slash key.
NN You can move to a specific line by typing g followed by the line number, as in g50 to go
to line 50.
q to exit the program

Front 80

Extracting Text (cmd)

Back 80

cut command extracts portions of input lines and displays them on standard output

Front 81

cut by byte
cut by character
cut by fiels

Back 81

By byte The -b list or --bytes=list
By character The -c list or --characters=list The -f list or --fields=list option cuts the specified list of fields from the input
file.

Front 82

extract the mac address from ifconfig using grep and cut

Back 82

$ ifconfig eth0 | grep HWaddr | cut -d “ “ -f 11

Front 83

Obtaining a Word Count

Back 83

wc file.txt
308 2343 15534 file.txt
limit the output
--lines (-l), --words (-w), --bytes (-c), or --chars (-m)

Front 84

command that searches for files that contain a specified string and returns the name of the file and (if it’s a text file) a line of context for that string

Back 84

grep [options] regexp [files]

Front 85

grep Count matching lines

grep Specify a pattern input file

Back 85

Count matching lines Instead of displaying context lines, grep displays the number of
lines that match the specified pattern if you use the -c or --count option.

Specify a pattern input file The -f file or --file=file option takes pattern input from
the specified file rather than from the command line.

Front 86

grep Ignore case

grep Search recursively

Back 86

Ignore case You can perform a case-insensitive search, rather than the default case-sensitive
search, by using the -i or --ignore-case option.

Search recursively The -r or --recursive option searches in the specified directory and
all subdirectories rather than simply the specified directory. You can use rgrep rather than
specify this option.

Front 87

grep Use an extended regular expression

Back 87

Use an extended regular expression The grep command interprets regexp as a basic regular
expression by default. To use an extended regular expression, you can pass the -E or
--extended-regexp option. Alternatively, you can call egrep rather than grep; this variant
command uses extended regular expressions by default.

Front 88

finds all the files in /etc that contain the string eth0

Back 88

$ grep -r eth0 /etc/*

-r option, it searches recursively, so files in subdirectories of /etc are examined as well as those in /etc itself.

Front 89

you want to locate all the files in /etc that contain the string
eth0 or eth1

Back 89

$ grep eth[01] /etc/*

Front 90

searches all files in /etc that contain the hostname twain.
example.com or bronto.pangaea.edu and, later on the same line, the number 127. This task
requires using several of the regular expression features.

Back 90

$ grep -E “(twain\.example\.com|bronto\.pangaea\.edu).*127” /etc/*

Front 91

shell quoting

Back 91

Because
the shell uses certain characters, such as the vertical bar and the asterisk, for its own purposes,
you must enclose certain regular expressions in quotes lest the shell attempt to parse
the regular expression as shell commands.

$ grep -E “(twain\.example\.com|bronto\.pangaea\.edu).*127” /etc/*

Front 92

you want to find the process
ID (PID) of a running xterm

Back 92

You can use a pipe to send the result of a ps command through grep
# ps ax | grep xterm

Front 93

sed (cmd)

Back 93

sed command directly modifies the contents of files, sending the changed file to standard
output. Its syntax can take one of two forms:
sed [options] -f script-file [input-file]
sed [options] script-text [input-file]

Front 94

sed cmd addresses explanation

Back 94

sed commands operate on
addresses, which are line numbers. Commands may take no addresses, in which case they operate on the entire file; one address, in which case they operate on the specified line; or two addresses (a range), in which case they operate on that range of lines, inclusive

Front 95

sed cmd Append text to the file.

sed cmd Append text to the file.

sed cmd Append text to the file

Back 95

a\text - 0|1 - Append text to the file

i\text - 0|1 - Insert text into the file

r filename - 0|1 - Append text from filename into the file

Front 96

sed cmd Replace the selected range of lines with the
provided text

sed Replace text that matches the regular expression
(regexp) with replacement.

Back 96

c\text - Range - Replace the selected range of lines with the
provided text.

s/regexp/replacement - Range - Replace text that matches the regular expression
(regexp) with replacement.

Front 97

sed write the current pattern space to the specified file

sed immediately quit the script, but print the current pattern space

sed immdeiately quit the scropt

Back 97

w filename - Range - Write the current pattern space to the
specified file
q - 0|1 - Immediately quit the script, but print the current
pattern space
Q - 0|1 - Immediately quit the script

Front 98

command processes the input file, cal-2008.txt, using sed’s s command to replace
the first occurrence of 2008 on each line with 2009.

Back 98

$ sed ‘s/2008/2009/‘ cal-2008.txt > cal-2009.txt

By default, sed sends the modified file to standard output,
so this example uses redirection to send the output to cal-2009.txt. The idea in this
example is to quickly convert a file created for the year 2008 so that it can be used in 2009.