Linux+ GNU and Linux Commands

Work On the Command Line

Text searching

*- match 0 or any in filenames

?-  Match single character in file name

[abcde] – Match any listed characters

[a-g] – Match range of characters

[!abcde] – Match any characters not listed

[!a-e] – Match any characters non in range 

[cat,dog,car] – Match any word in list

[$] – lis file names ending preceding the $ character

Ex: ll xfs*

ll xfs[a-e]

Ex : count lines ll -l wc

Tab used to autocompletion.

Meta characters and control characters.

|| – Logical OR

&& –  Logical &&

; –  separate multiple command at single line


cd /usr/share; ll; df -h;

Can divide commands to multiple lines using \

ll /usr/share\


is equal to 

ll /usr/share/xml

Single Shell Command and one line command sequences

To print all environment  varriables


To print specific environment varriable

echo $PATH

echo $UID

Get system information

uname -a 

Get current user IDs


-i for ignore case

cat /var/log/messages | grep -i error

Get error counts

cat /var/log/messages | grep -i error | wc -l

Print Working Directory


Using and Modifying Environment Varriables

Print current user

echo $USER

Print current shell type

echo $SHELL

To go to home directory

cd ~

Have to set and export the varibale to be used in shell

TEST=Hi; export TEST

echo $TEST


Use and Edit command HIistory,  and PATH

Show last 15 commands

history 15

Show last command


Shows most recent command starting with string


Show most recent command containing string


Defining a PATH

PATH=$PATH:/my/folder; export PATH

Process Text Streams Using Filters

Send output of one command as an input to another command

ll | sort

ll | grep file1

Redirect out put, typically fo a file

ll | sort > out.txt

Note : single > create a new file, >> appends to existing data

Specify input 


Output input stream or file to stdout

Eg: to check lines in a file

cat files.txt | wc -l

Display files in octal format


Dividing large files

Eg: Split file by line numbers

split -l 200 files.txt

Eg: Split based on chunk numbers

split -n 5 files.txt

Eg: Split based on file size

split -b 100M files.txt

Counts words of lines of the input stream


Eg: count words in file

cat files.txt | wc -w

see man wc for more options

Display top or bottom of the file

head or tail

Convert spaces into tabs ot the reverse

expand unexpand

Change/convert case of character

Eg: ABCDEFGHIJKLMN in file texts.txt

cat texts.txt | tr “[A-G]” “[a-g]”

output : abcdefgHIJKLMN

Formats data for printing

pr file.txt|more

• The number lines (nl) command assigns a number to each line of output 

Eg: Add lines to a file and create new file with numbers

nl files.txt > line_files.txt

• Text files can be reformatted to a specified width using the fmt command 

Eg: Format contents of a file in the width of 40 characters

fmt -w 40 files.txt

• Numerical or lexigraphical sorting can be performed with the sort command 

sort -n files_with_numbers_at_leading.txt

• The uniq command will remove duplicate entries from its input 

to avoid duplicates on above -nu

• Filtering out specific columns from a file can be done with the cut command 

Eg: to view specific(1, 3) columns of a comma separated or other delimiter files

cat files.txt | cut -d “,” -f 1,3

• Lines from multiple files can be joined with the paste command 

merge files based on lines side by side

paste file1.txt file2.txt

• Multiple files can be assembled with the join command 

Join command joins common fields in the output

join file1.txt file2.txt

join command asks for files to be sorted before joining. by tasing ‘no check’ could skip this

• The Stream EDitor (sed) uses regular expressions for modifying text 

replace “this” with “that”

cat files.txt | sed -e “s/this/that/”

multiple replacement on same line also can be done

• The diff command allows comparison of two files 

diff file2.txt file2.txt

Perform Basic File Management

Make directory/ parent directories as needed

mkdir -p /dir1/dir2/dir3

Create an empty file

touch file1

> file1

Copy file to my current directory

cp /tmp/mydir .

Note: ls -lrt shows more recent file at the bottom

Recursively Copy File/Direcory

cp -R /tmp/mydir /home/

Copy all directories(starts with ‘dir’) and contents into a directory named ‘pack’

cp -R dir* pack

Move and optionally rename files. -t for target directory

mv /tmp/mydir -t /home/hisdir

Remove files with rm

rm -rf /tmp/mydir

to remove parent directory

rmdir -p /tmp/mydir

to remove all subdirectories and files without prompting

rm -drf dir1

Use simple and advances wildcard specifications in commands

List files and directories with some charecters in name

ls /etc/pa*s*d


 ls /tmp/*[!r].ser*

touch command can update a timestamp or create a new file

touch filename

touch -d 9am filename

touch -d “2 days ago 17:30” filename

touch -d “15 Jan” filename

The file command identifies the type of a file

file filename

file /sbin/*

find command helps to locate and act on the files base  on type, size or time

Eg; find all configuration file

find / -name *.conf

Eg: find files begins with “system” in directory /tmp

find /tmp -name “system*”

Eg:  Find regular files within /tmp 

find /tmp -type f

Eg: Find directories within /tmp

find /tmp -type d

Eg; Find deepest files and folders in hierarchy

find /usr -depth

Eg: Find files greater than 100MB

find /usr -size +100M

Eg; find files accessed within last 3 days

find /usr -atime 3

Eg: find file in /usr those are owned by the user root

find /usr -user root

Eg: find file in /usr those used within last 3 days, and long list with -lrt

find /usr -atime 3 -exec ls -lrt “{}” \;

Eg: find recursively in current directory

find . -name “*.gz”

File Compression and Decompression

Using gzip to compress files and gunzip to decompress


gzip /tmp/myfile*

Better compression

gzip -9 /home/user/data.gz

Faster compressiont

gzip -1 /home/user/data.gz

View contents of a gz

gzip -l data.gz


gunzip /home/user/data.gz

The bzip2 utility operates the same as gzip and gunzip. but uses different compression algorithm.


bzip2 Events_admin_2019-07-06_scnd.csv


bzip2 -d Events_admin_2019-07-06_scnd.bz2

The xz utiliy is also available for compressing or decompressing files

xz file.txt

unxz file.txt

Usage of TAR, CPIO(Copy in and out) and DD


Archieve in TAR

Eg: Add all files begin with TLD to a tar

tar -cvf mytar.tar TLP*

c – create

v – verbose

f – flename

Inspect tar

tar -tvf mytar.tar

-t list 


tar -xvf mytar.tar


Find files stat with TLP and add to archieve

find . -name “TLP*” | cpio -ov > mycp.cpio

Re put files thos archieved earlier

cpio -iv < mycp.cpio

Eg; find everything start eith TLP and move to a new dir

find . -name “TLP*” | cpio -pvd ./test

-p pass through

-d directory


convert and copy a file

dd if=/dev/zero of=zero.txt bs=10M count=10

if – input file

of – output file

bs – byte size

Read from from one device to another

dd if=/dev/sda1 of=/media/usb -bs=10M count=10

Use the output of one command as the input to another command

ls | xargs echo My Files:

ls | xargs ls -lia

Eg: find all text files and delete

find /tmp -name *.txt | xargs rm -f

Send output to both stdout and files

Eg; Redirect Error to a different file

ls /sbin/* > sbin.txt 2> sbin.err

Eg: translate output capitalize output of a file

tr ‘a-z’ ‘A-Z’ < sbin.txt

Tee command read from stdin and writes to stdout and files.

netstat -an | tee netstat.txt

ls /tmp | tee tmp1.txt tmp1.txt

Create Monitor and kill process

To run job at background, add & at the end of the command

sleep 100&

sleep 200&

sleep 500&

To view jobs running in background

jobs -l 

Jobs are belongs to particular instance of a terminal.

When a bg job brought into foreground, it’s priority increases

fg 1

Ctrl + z stops the job

to re run a stoped job 

bg 1

To run program ofter logout use nuhup command.

outputs saved to nohup.out by default

Eg: run a program after logout and save the errors to a different file

nohup> ~/meerr.err &

1> standard output

2> standard error

Monitor Active Processes

ps command is the direct command

ps -ef gives full programs being run and executed commands

Processes used by user root

ps -u root

process used by the group admin

ps -g admin

process used specific ports

ps -p 443 3433

find processes by name

ps -ef | grep systemd

search for the process id of a process

pidof systemd

search  by name

pgrep sleep

List Column Names


Show each process related to bash

ps -ef | grep -i bash

top command give interact-ability 

z – color change

b – bold high priority processes

c – order by cpu usage

m – memory

u -user 

shft + l – highlight specific strings in process list

k – kill a process

r – renice a process

e – shows more usages

Kill Process

kill job number

kill %1

kill pid

kill 9939

kill with signal

kill -9 9939

kill -SIGTERM 9939

Modify Process Execution Priorities

Know the default priority of the job created

Run program with higher or lower priority than the default priority

Change the priority of the running process

Default priority for the most process is 20

ps -el shows priority in 8th column

run ‘nice’ command to check the current value


nice -n -10 sleep 600&

nice -n 10 sleep 600&


shift + l to filter (enter sleep)

r to modify priorities


renice 10 [pid]

Search Text Files Using Regular Expressions


grep error /var/log/messages

— search for word error in messages log

grep -v error /var/log/messages

— invert above search. other than word ‘error’

grep -i error /var/log/messages

— ignore case

Regex Search

grep ^root /etc/passwd

— search for the word ‘root’ at the beginning of the line

egrep ‘^[a-d]’ /etc/passwd

— search the letter range a to be, at the beginning of the line

grep error –color /

— highlight searches

egrep ‘[0-9]{4}’ /var/log/messages

— find numbers with 4 digits

grep -F ‘nologin’ /etc/passwd

— search for fixed characters

grep -F -f users.txt passwd.txt

— searches words in users.txt exists in passwd.txt

Perform Basic File Editing Operations Using VI

gg – top of the file

VI Modes

Command Mode

— used to navigate the file

— search the file

— Replace

— Delete

— Copy and paste

— Send commands to execute mode

Editing Mode

Data is typed into editor

d twice to delete a line

5dd — to detele 5 lines

Shift + — Open a line above to insert

yy – copy

p – put/paste

5yy – copy five lines and ‘p’ to put/paste

Shift + a — insert mode at the end of the line

Shift + i — insert mode at the beginning of the line

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