Need help with bash-guide?
Click the “chat” button below for chat support from the developer who created it, or find similar developers for support.

About the developer

Idnan
9.9K Stars 922 Forks 85 Commits 22 Opened issues

Description

A guide to learn bash

Services available

!
?

Need anything else?

Contributors list

No Data

bash logo

Table of Contents

  1. Basic Operations
    1.1. File Operations
    1.2. Text Operations
    1.3. Directory Operations
    1.4. SSH, System Info & Network Operations
    1.5. Process Monitoring Operations
  2. Basic Shell Programming
    2.1. Variables
    2.2. Array
    2.3. String Substitution
    2.4. Functions
    2.5. Conditionals
    2.6. Loops
  3. Tricks
  4. Debugging

1. Basic Operations

a.
export

Displays all environment variables. If you want to get details of a specific variable, use

echo $VARIABLE_NAME
.
bash
export
Example: ```bash $ export AWSHOME=/Users/adnanadnan/.aws LANG=enUS.UTF-8 LCCTYPE=enUS.UTF-8 LESS=-R

$ echo $AWS_HOME /Users/adnanadnan/.aws ```

b.
whatis

whatis shows description for user commands, system calls, library functions, and others in manual pages

bash
whatis something
Example:
bash
$ whatis bash
bash (1)             - GNU Bourne-Again SHell

c.
whereis

whereis searches for executables, source files, and manual pages using a database built by system automatically.

bash
whereis name
Example:
bash
$ whereis php
/usr/bin/php

d.
which

which searches for executables in the directories specified by the environment variable PATH. This command will print the full path of the executable(s).

bash
which program_name 
Example:
bash
$ which php
/c/xampp/php/php

e. clear

Clears content on window.

1.1. File Operations

cat chmod chown cp diff file find gunzip gzcat gzip head
lpq lpr lprm ls more mv rm tail touch

a.
cat

It can be used for the following purposes under UNIX or Linux.
* Display text files on screen * Copy text files
* Combine text files
* Create new text files

bash
cat filename
cat file1 file2 
cat file1 file2 > newcombinedfile
cat < file1 > file2 #copy file1 to file2

b.
chmod

The chmod command stands for "change mode" and allows you to change the read, write, and execute permissions on your files and folders. For more information on this command check this link.

bash
chmod -options filename

c.
chown

The chown command stands for "change owner", and allows you to change the owner of a given file or folder, which can be a user and a group. Basic usage is simple forward first comes the user (owner), and then the group, delimited by a colon.

bash
chown -options user:group filename

d.
cp

Copies a file from one location to other.

bash
cp filename1 filename2
Where
filename1
is the source path to the file and
filename2
is the destination path to the file.

e.
diff

Compares files, and lists their differences.

bash
diff filename1 filename2

f.
file

Determine file type.

bash
file filename
Example:
bash
$ file index.html
 index.html: HTML document, ASCII text

g.
find

Find files in directory

bash
find directory options pattern
Example:
bash
$ find . -name README.md
$ find /home/user1 -name '*.png'

h.
gunzip

Un-compresses files compressed by gzip.

bash
gunzip filename

i.
gzcat

Lets you look at gzipped file without actually having to gunzip it.

bash
gzcat filename

j.
gzip

Compresses files.

bash
gzip filename

k.
head

Outputs the first 10 lines of file

bash
head filename

l.
lpq

Check out the printer queue.

bash
lpq
Example:
bash
$ lpq
Rank    Owner   Job     File(s)                         Total Size
active  adnanad 59      demo                            399360 bytes
1st     adnanad 60      (stdin)                         0 bytes

m.
lpr

Print the file.

bash
lpr filename

n.
lprm

Remove something from the printer queue.

bash
lprm jobnumber

o.
ls

Lists your files.

ls
has many options:
-l
lists files in 'long format', which contains the exact size of the file, who owns the file, who has the right to look at it, and when it was last modified.
-a
lists all files, including hidden files. For more information on this command check this link.
bash
ls option
Example:
$ ls -la
rwxr-xr-x   33 adnan  staff    1122 Mar 27 18:44 .
drwxrwxrwx  60 adnan  staff    2040 Mar 21 15:06 ..
[email protected]  1 adnan  staff   14340 Mar 23 15:05 .DS_Store
-rw-r--r--   1 adnan  staff     157 Mar 25 18:08 .bumpversion.cfg
-rw-r--r--   1 adnan  staff    6515 Mar 25 18:08 .config.ini
-rw-r--r--   1 adnan  staff    5805 Mar 27 18:44 .config.override.ini
drwxr-xr-x  17 adnan  staff     578 Mar 27 23:36 .git
-rwxr-xr-x   1 adnan  staff    2702 Mar 25 18:08 .gitignore

p.
more

Shows the first part of a file (move with space and type q to quit).

bash
more filename

q.
mv

Moves a file from one location to other.

bash
mv filename1 filename2
Where
filename1
is the source path to the file and
filename2
is the destination path to the file.

Also it can be used for rename a file.

bash
mv old_name new_name

r.
rm

Removes a file. Using this command on a directory gives you an error.

rm: directory: is a directory
To remove a directory you have to pass
-r
which will remove the content of the directory recursively. Optionally you can use
-f
flag to force the deletion i.e. without any confirmations etc.
bash
rm filename

s.
tail

Outputs the last 10 lines of file. Use

-f
to output appended data as the file grows.
bash
tail filename

t.
touch

Updates access and modification time stamps of your file. If it doesn't exists, it'll be created.

bash
touch filename
Example:
bash
$ touch trick.md

1.2. Text Operations

awk cut echo egrep fgrep fmt grep nl sed sort
tr uniq wc

a.
awk

awk is the most useful command for handling text files. It operates on an entire file line by line. By default it uses whitespace to separate the fields. The most common syntax for awk command is

awk '/search_pattern/ { action_to_take_if_pattern_matches; }' file_to_parse

Lets take following file

/etc/passwd
. Here's the sample data that this file contains:
root:x:0:0:root:/root:/usr/bin/zsh
daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin
bin:x:2:2:bin:/bin:/usr/sbin/nologin
sys:x:3:3:sys:/dev:/usr/sbin/nologin
sync:x:4:65534:sync:/bin:/bin/sync
So now lets get only username from this file. Where
-F
specifies that on which base we are going to separate the fields. In our case it's
:
.
{ print $1 }
means print out the first matching field.
bash
awk -F':' '{ print $1 }' /etc/passwd
After running the above command you will get following output.
root
daemon
bin
sys
sync
For more detail on how to use
awk
, check following link.

b.
cut

Remove sections from each line of files

example.txt

bash
red riding hood went to the park to play

show me columns 2 , 7 , and 9 with a space as a separator

bash
cut -d " " -f2,7,9 example.txt
bash
riding park play

c.
echo

Display a line of text

display "Hello World"

bash
echo Hello World
bash
Hello World

display "Hello World" with newlines between words

bash
echo -ne "Hello\nWorld\n"
bash
Hello
World

d.
egrep

Print lines matching a pattern - Extended Expression (alias for: 'grep -E')

example.txt

bash
Lorem ipsum
dolor sit amet, 
consetetur
sadipscing elitr,
sed diam nonumy
eirmod tempor
invidunt ut labore
et dolore magna
aliquyam erat, sed
diam voluptua. At
vero eos et
accusam et justo
duo dolores et ea
rebum. Stet clita
kasd gubergren,
no sea takimata
sanctus est Lorem
ipsum dolor sit
amet.

display lines that have either "Lorem" or "dolor" in them.

bash
egrep '(Lorem|dolor)' example.txt
or
grep -E '(Lorem|dolor)' example.txt
bash
Lorem ipsum
dolor sit amet,
et dolore magna
duo dolores et ea
sanctus est Lorem
ipsum dolor sit

e.
fgrep

Print lines matching a pattern - FIXED pattern matching (alias for: 'grep -F')

example.txt

bash
Lorem ipsum
dolor sit amet,
consetetur
sadipscing elitr,
sed diam nonumy
eirmod tempor
foo (Lorem|dolor) 
invidunt ut labore
et dolore magna
aliquyam erat, sed
diam voluptua. At
vero eos et
accusam et justo
duo dolores et ea
rebum. Stet clita
kasd gubergren,
no sea takimata
sanctus est Lorem
ipsum dolor sit
amet.

Find the exact string '(Lorem|dolor)' in example.txt

bash
fgrep '(Lorem|dolor)' example.txt
or
grep -F '(Lorem|dolor)' example.txt
bash
foo (Lorem|dolor) 

f.
fmt

Simple optimal text formatter

example: example.txt (1 line)

bash
Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy eirmod tempor invidunt ut labore et dolore magna aliquyam erat, sed diam voluptua. At vero eos et accusam et justo duo dolores et ea rebum. Stet clita kasd gubergren, no sea takimata sanctus est Lorem ipsum dolor sit amet.

output the lines of example.txt to 20 character width

bash
cat example.txt | fmt -w 20
bash
Lorem ipsum
dolor sit amet,
consetetur
sadipscing elitr,
sed diam nonumy
eirmod tempor
invidunt ut labore
et dolore magna
aliquyam erat, sed
diam voluptua. At
vero eos et
accusam et justo
duo dolores et ea
rebum. Stet clita
kasd gubergren,
no sea takimata
sanctus est Lorem
ipsum dolor sit
amet.

g.
grep

Looks for text inside files. You can use grep to search for lines of text that match one or many regular expressions, and outputs only the matching lines.

bash
grep pattern filename
Example:
bash
$ grep admin /etc/passwd
_kadmin_admin:*:218:-2:Kerberos Admin Service:/var/empty:/usr/bin/false
_kadmin_changepw:*:219:-2:Kerberos Change Password Service:/var/empty:/usr/bin/false
_krb_kadmin:*:231:-2:Open Directory Kerberos Admin Service:/var/empty:/usr/bin/false
You can also force grep to ignore word case by using
-i
option.
-r
can be used to search all files under the specified directory, for example:
bash
$ grep -r admin /etc/
And
-w
to search for words only. For more detail on
grep
, check following link.

h.
nl

Number lines of files

example.txt

bash
Lorem ipsum
dolor sit amet,
consetetur
sadipscing elitr,
sed diam nonumy
eirmod tempor
invidunt ut labore
et dolore magna
aliquyam erat, sed
diam voluptua. At
vero eos et
accusam et justo
duo dolores et ea
rebum. Stet clita
kasd gubergren,
no sea takimata
sanctus est Lorem
ipsum dolor sit
amet.

show example.txt with line numbers

bash
nl -s". " example.txt 
bash
     1. Lorem ipsum
     2. dolor sit amet,
     3. consetetur
     4. sadipscing elitr,
     5. sed diam nonumy
     6. eirmod tempor
     7. invidunt ut labore
     8. et dolore magna
     9. aliquyam erat, sed
    10. diam voluptua. At
    11. vero eos et
    12. accusam et justo
    13. duo dolores et ea
    14. rebum. Stet clita
    15. kasd gubergren,
    16. no sea takimata
    17. sanctus est Lorem
    18. ipsum dolor sit
    19. amet.

i.
sed

Stream editor for filtering and transforming text

example.txt

bash
Hello This is a Test 1 2 3 4

replace all spaces with hyphens

bash
sed 's/ /-/g' example.txt
bash
Hello-This-is-a-Test-1-2-3-4

replace all digits with "d"

bash
sed 's/[0-9]/d/g' example.txt
bash
Hello This is a Test d d d d

j.
sort

Sort lines of text files

example.txt

bash
f
b
c
g
a
e
d

sort example.txt

bash
sort example.txt
bash
a
b
c
d
e
f
g

randomize a sorted example.txt

bash
sort example.txt | sort -R
bash
b
f
a
c
d
g
e

k.
tr

Translate or delete characters

example.txt

bash
Hello World Foo Bar Baz!

take all lower case letters and make them upper case

bash
cat example.txt | tr 'a-z' 'A-Z' 
bash
HELLO WORLD FOO BAR BAZ!

take all spaces and make them into newlines

bash
cat example.txt | tr ' ' '\n'
bash
Hello
World
Foo
Bar
Baz!

l.
uniq

Report or omit repeated lines

example.txt

bash
a
a
b
a
b
c
d
c

show only unique lines of example.txt (first you need to sort it, otherwise it won't see the overlap)

bash
sort example.txt | uniq
bash
a
b
c
d

show the unique items for each line, and tell me how many instances it found

bash
sort example.txt | uniq -c
bash
    3 a
    2 b
    2 c
    1 d

m.
wc

Tells you how many lines, words and characters there are in a file.

bash
wc filename
Example:
bash
$ wc demo.txt
7459   15915  398400 demo.txt
Where
7459
is lines,
15915
is words and
398400
is characters.

1.3. Directory Operations

cd mkdir pwd

a.
cd

Moves you from one directory to other. Running this

bash
$ cd
moves you to home directory. This command accepts an optional
dirname
, which moves you to that directory.
bash
cd dirname

b.
mkdir

Makes a new directory.

bash
mkdir dirname
You can use this to create multiple directories at once within your current directory.
bash
mkdir 1stDirectory 2ndDirectory 3rdDirectory
You can also use this to create parent directories at the same time. For instance, if you wanted a directory named 'project1' in another subdirectory at '/samples/bash/projects/', you could run:
bash 
mkdir /samples/bash/projects/project1
If any of these directories did no already exist, they would be created as well.

c.
pwd

Tells you which directory you currently are in.

bash
pwd

1.4. SSH, System Info & Network Operations

bg cal date df dig du fg finger jobs last
man passwd ping ps quota scp ssh top uname uptime
w wget whoami whois

a.
bg

Lists stopped or background jobs; resume a stopped job in the background.

b.
cal

Shows the month's calendar.

c.
date

Shows the current date and time.

d.
df

Shows disk usage.

e.
dig

Gets DNS information for domain.

bash
dig domain

f.
du

Shows the disk usage of files or directories. For more information on this command check this link

bash
du [option] [filename|directory]
Options: -
-h
(human readable) Displays output it in kilobytes (K), megabytes (M) and gigabytes (G). -
-s
(supress or summarize) Outputs total disk space of a directory and supresses reports for subdirectories.

Example:

bash
du -sh pictures
1.4M pictures

g.
fg

Brings the most recent job in the foreground.

h.
finger

Displays information about user.

bash
finger username

i.
jobs

Lists the jobs running in the background, giving the job number.

j.
last

Lists your last logins of specified user.

bash
last yourUsername

k.
man

Shows the manual for specified command.

bash
man command

l.
passwd

Allows the current logged user to change their password.

m.
ping

Pings host and outputs results.

bash
ping host

n.
ps

Lists your processes.

bash
ps -u yourusername
Use the flags ef. e for every process and f for full listing.
bash
ps -ef

o.
quota

Shows what your disk quota is.

bash
quota -v

p.
scp

Transfer files between a local host and a remote host or between two remote hosts.

copy from local host to remote host

bash
scp source_file [email protected]:directory/target_file
copy from remote host to local host
bash
scp [email protected]:directory/source_file target_file
scp -r [email protected]:directory/source_folder target_folder
This command also accepts an option
-P
that can be used to connect to specific port.
bash
scp -P port [email protected]:directory/source_file target_file

q.
ssh

ssh (SSH client) is a program for logging into and executing commands on a remote machine.

bash
ssh [email protected]
This command also accepts an option
-p
that can be used to connect to specific port.
bash
ssh -p port [email protected]

r.
top

Displays your currently active processes.

s.
uname

Shows kernel information.

bash
uname -a

t.
uptime

Shows current uptime.

u.
w

Displays who is online.

v.
wget

Downloads file.

bash
wget file

w.
whoami

Return current logged in username.

x.
whois

Gets whois information for domain.

bash
whois domain

1.5. Process Monitoring Operations

kill killall & nohup

a.
kill

Kills (ends) the processes with the ID you gave.

bash
kill PID

b.
killall

Kill all processes with the name.

bash
killall processname

c. &

The

&
symbol instructs the command to run as a background process in a subshell.
bash
command &

d.
nohup

nohup stands for "No Hang Up". This allows to run command/process or shell script that can continue running in the background after you log out from a shell.

bash
nohup command
Combine it with
&
to create background processes
bash
nohup command &

2. Basic Shell Programming

The first line that you will write in bash script files is called

shebang
. This line in any script determines the script's ability to be executed like a standalone executable without typing sh, bash, python, php etc beforehand in the terminal.
#!/usr/bin/env bash

2.1. Variables

Creating variables in bash is similar to other languages. There are no data types. A variable in bash can contain a number, a character, a string of characters, etc. You have no need to declare a variable, just assigning a value to its reference will create it.

Example:

bash
str="hello world"

The above line creates a variable

str
and assigns "hello world" to it. The value of variable is retrieved by putting the
$
in the beginning of variable name.

Example:

bash
echo $str   # hello world

2.2. Array

Like other languages bash has also arrays. An array is a variable containing multiple values. There's no maximum limit on the size of array. Arrays in bash are zero based. The first element is indexed with element 0. There are several ways for creating arrays in bash which are given below.

Examples:

bash
array[0]=val
array[1]=val
array[2]=val
array=([2]=val [0]=val [1]=val)
array=(val val val)
To display a value at specific index use following syntax:
${array[i]}     # where i is the index

If no index is supplied, array element 0 is assumed. To find out how many values there are in the array use the following syntax:

${#array[@]}

Bash has also support for the ternary conditions. Check some examples below.

${varname:-word}    # if varname exists and isn't null, return its value; otherwise return word
${varname:=word}    # if varname exists and isn't null, return its value; otherwise set it word and then return its value
${varname:+word}    # if varname exists and isn't null, return word; otherwise return null
${varname:offset:length}    # performs substring expansion. It returns the substring of $varname starting at offset and up to length characters

2.3 String Substitution

Check some of the syntax on how to manipulate strings

${variable#pattern}         # if the pattern matches the beginning of the variable's value, delete the shortest part that matches and return the rest
${variable##pattern}        # if the pattern matches the beginning of the variable's value, delete the longest part that matches and return the rest
${variable%pattern}         # if the pattern matches the end of the variable's value, delete the shortest part that matches and return the rest
${variable%%pattern}        # if the pattern matches the end of the variable's value, delete the longest part that matches and return the rest
${variable/pattern/string}  # the longest match to pattern in variable is replaced by string. Only the first match is replaced
${variable//pattern/string} # the longest match to pattern in variable is replaced by string. All matches are replaced
${#varname}     # returns the length of the value of the variable as a character string

2.4. Functions

As in almost any programming language, you can use functions to group pieces of code in a more logical way or practice the divine art of recursion. Declaring a function is just a matter of writing function myfunc { mycode }. Calling a function is just like calling another program, you just write its name.

function name() {
    shell commands
}

Example: ```bash

!/bin/bash

function hello { echo world! } hello

function say { echo $1 } say "hello world!" ```

When you run the above example the

hello
function will output "world!". The above two functions
hello
and
say
are identical. The main difference is function
say
. This function, prints the first argument it receives. Arguments, within functions, are treated in the same manner as arguments given to the script.

2.5. Conditionals

The conditional statement in bash is similar to other programming languages. Conditions have many form like the most basic form is

if
expression
then
statement where statement is only executed if expression is true.
if [ expression ]; then
    will execute only if expression is true
else
    will execute if expression is false
fi

Sometime if conditions becoming confusing so you can write the same condition using the

case statements
.
case expression in
    pattern1 )
        statements ;;
    pattern2 )
        statements ;;
    ...
esac

Expression Examples:

statement1 && statement2  # both statements are true
statement1 || statement2  # at least one of the statements is true

str1=str2 # str1 matches str2 str1!=str2 # str1 does not match str2 str1str2 # str1 is greater than str2 -n str1 # str1 is not null (has length greater than 0) -z str1 # str1 is null (has length 0)

-a file # file exists -d file # file exists and is a directory -e file # file exists; same -a -f file # file exists and is a regular file (i.e., not a directory or other special type of file) -r file # you have read permission -s file # file exists and is not empty -w file # you have write permission -x file # you have execute permission on file, or directory search permission if it is a directory -N file # file was modified since it was last read -O file # you own file -G file # file's group ID matches yours (or one of yours, if you are in multiple groups)

file1 -nt file2 # file1 is newer than file2 file1 -ot file2 # file1 is older than file2

-lt # less than -le # less than or equal -eq # equal -ge # greater than or equal -gt # greater than -ne # not equal

2.6. Loops

There are three types of loops in bash.

for
,
while
and
until
.

Different

for
Syntax: ```bash for x := 1 to 10 do begin statements end

for name [in list] do statements that can use $name done

for (( initialisation ; ending condition ; update )) do statements... done ```

while
Syntax:
bash
while condition; do
  statements
done

until
Syntax:
bash
until condition; do
  statements
done

3. Tricks

Set an alias

Run

nano ~/.bash_profile
and add the following line:
alias dockerlogin='ssh [email protected] -p2222'  # add your alias in .bash_profile

To quickly go to a specific directory

Run

nano ~/.bashrc
and add the following line:
export hotellogs="/workspace/hotel-api/storage/logs"

Now you can use the saved path:

source ~/.bashrc
cd $hotellogs

Re-execute the previous command

This goes back to the days before you could rely on keyboards to have an "up" arrow key, but can still be useful. To run the last command in your history

bash
!!
A common error is to forget to use
sudo
to prefix a command requiring privileged execution. Instead of typing the whole command again, you can:
bash
sudo !!
This would change a
mkdir somedir
into
sudo mkdir somedir
.

Exit traps

Make your bash scripts more robust by reliably performing cleanup.

function finish {
  # your cleanup here. e.g. kill any forked processes
  jobs -p | xargs kill
}
trap finish EXIT

Saving your environment variables

When you do

export FOO = BAR
, your variable is only exported in this current shell and all its children, to persist in the future you can simply append in your
~/.bash_profile
file the command to export your variable
bash
echo export FOO=BAR >> ~/.bash_profile

Accessing your scripts

You can easily access your scripts by creating a bin folder in your home with

mkdir ~/bin
, now all the scripts you put in this folder you can access in any directory.

If you can not access, try append the code below in your

~/.bash_profile
file and after do
source ~/.bash_profile
. ```bash

set PATH so it includes user's private bin if it exists

if [ -d "$HOME/bin" ] ; then PATH="$HOME/bin:$PATH" fi ```

4. Debugging

You can easily debug the bash script by passing different options to

bash
command. For example
-n
will not run commands and check for syntax errors only.
-v
echo commands before running them.
-x
echo commands after command-line processing.
bash -n scriptname
bash -v scriptname
bash -x scriptname

Contribution

  • Report issues How to
  • Open pull request with improvements How to
  • Spread the word

Translation

License

License: CC BY 4.0

We use cookies. If you continue to browse the site, you agree to the use of cookies. For more information on our use of cookies please see our Privacy Policy.