Bash Guide

originally from Idnan/bash-guide

---

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. Other String Tricks
   2.5. Functions
   2.6. Conditionals
   2.7. Loops
   2.8. Regex
   2.9. Pipes
3. Tricks
4. Debugging
5. Multi-threading

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
AWS_HOME=/Users/adnanadnan/.aws
LANG=en_US.UTF-8
LC_CTYPE=en_US.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
less	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. less

Shows the contents of a file or a command output, one page at a time. It is similar to more, but has more advanced features and allows you to navigate both forward and backward through the file.

Bash

less filename

m. 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

n. lpr

Print the file.

Bash

lpr filename

o. lprm

Remove something from the printer queue.

Bash

lprm jobnumber

p. 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 ..
-rw-r--r--@  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

q. more

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

Bash

more filename

r. 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

s. 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

t. tail

Outputs the last 10 lines of file. Use -f to output appended data as the file grows.

Bash

tail filename

u. 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

Bash

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:

Text Only

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.

Text Only

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

Switch to the previous working directory

Bash

cd -

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 with the -p (or --parents) flag. For instance, if you wanted a directory named 'project1' in another subdirectory at '/samples/bash/projects/', you could run:

Bash

mkdir -p /samples/bash/projects/project1
mkdir --parents /samples/bash/projects/project1

Both commands above will do the same thing.
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	sync	curl

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 user@host:directory/target_file

copy from remote host to local host

Bash

scp user@host:directory/source_file target_file
scp -r user@host: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 user@host: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 user@host

This command also accepts an option -p that can be used to connect to specific port.

Bash

ssh -p port user@host

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

y. rsync

Does the same job as scp command, but transfers only changed files. Useful when transferring the same folder to/from server multiple times.

Bash

rsync source_folder user@host:target_folder
rsync user@host:target_folder target_folder

z. curl

Curl is a command-line tool for requesting or sending data using URL syntax. Usefull on systems where you only have terminal available for making various requests.

Bash

curl url

Use -X or --request to specify which method you would like invoke (GET, POST, DELETE, ...).
Use -d <data> or --data <data> to POST data on given URL.

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.

Bash

#!/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:

Bash

${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:

Bash

${#array[@]}

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

Bash

${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

Bash

${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. Other String Tricks

Bash has multiple shorthand tricks for doing various things to strings.

Bash

${variable,,}    #this converts every letter in the variable to lowercase
${variable^^}    #this converts every letter in the variable to uppercase

${variable:2:8}  #this returns a substring of a string, starting at the character at the 2 index(strings start at index 0, so this is the 3rd character),
                 #the substring will be 8 characters long, so this would return a string made of the 3rd to the 11th characters.

Here are some handy pattern matching tricks

Bash

if [[ "$variable" == *subString* ]]  #this returns true if the provided substring is in the variable
if [[ "$variable" != *subString* ]]  #this returns true if the provided substring is not in the variable
if [[ "$variable" == subString* ]]   #this returns true if the variable starts with the given subString
if [[ "$variable" == *subString ]]   #this returns true if the variable ends with the given subString

The above can be shortened using a case statement and the IN keyword

Bash

case "$var" in
	begin*)
		#variable begins with "begin"
	;;
	*subString*)
		#subString is in variable
	;;

	*otherSubString*)
		#otherSubString is in variable
	;;
esac

2.5. 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 my_func { my_code }. Calling a function is just like calling another program, you just write its name.

Bash

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.

2.6. 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.

Bash

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.

Bash

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

Expression Examples:

Bash

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
str1<str2       # str1 is less than str2
str1>str2       # 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

2.7. Loops

There are three types of loops in bash. for, while and until.

Different for Syntax:

Bash

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

2.8. Regex

They are a powerful tool for manipulating and searching text. Here are some examples of regular expressions that use each metacharacter:

`.`(dot)

`*`(asterisk)

`+`(plus)

`?`(question mark)

`|`(pipe)

`[]`(character class)

`[^]`(negated character class)

`()`(grouping)

`{}`(quantifiers)

`\`(escape)

a. . (dot)

Matches any single character except newline.

Bash

grep h.t file.txt

Output:

Bash

hat
hot
hit

b. * (asterisk)

Matches zero or more occurrences of the preceding character or group.

Bash

grep ab*c file.txt

Output:

Bash

ac
abc
abbc
abbbc

c. + (plus)

Matches one or more occurrences of the preceding character or group.

Bash

grep ab+c file.txt

Output:

Bash

abc
abbc
abbbc
abbbbc

d. ? (question mark)

Matches zero or one occurrence of the preceding character or group.

Bash

grep ab?c file.txt

Output:

Bash

ac
abc

e. | (pipe)

Matches either the pattern to the left or the pattern to the right.

Bash

egrep "cat|dog" file.txt

Output:

Bash

cat
dog

f. [] (character class)

Matches any character inside the brackets.

Bash

[aeiou] will match any vowel
[a-z] will match any lowercase letter

g. [] (negated character class)

Matches any character not inside the brackets.

Bash

[^aeiou] will match any consonant
[^a-z] will match any non-lowercase letter

h. () (grouping)

Groups multiple tokens together and creates a capture group.

Bash

egrep "(ab)+" file.txt

Output:

Bash

ab
abab
ababab

i. {} (quantifiers)

Matches a specific number of occurrences of the preceding character or group.

Bash

egrep "a{3}" file.txt

Output:

Bash

aaa
aaaa
aaaaa

j. \ (escape)

Escapes the next character to match it literally.

Bash

egrep "a\+" file.txt

Output:

Bash

a+

=======

2.9. Pipes

Multiple commands can be linked together with a pipe, |. A | will send the standard-output from command A to the standard-input of command B.
Pipes can also be constructed with the |& symbols. This will send the standard-output and standard-error from command A to the standard-input of command B.

3. Tricks

Set an alias

Run nano ~/.bash_profile and add the following line:

Bash

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:

Bash

export hotellogs="/workspace/hotel-api/storage/logs"

Now you can use the saved path:

Bash

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.

Bash

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

bash -n scriptname
bash -v scriptname
bash -x scriptname

5. Multi-threading

You can easily multi-threading your jobs using &. All those jobs will then run in the background simultaneously and you can see the processes below are running using jobs.

Bash

sleep 15 & sleep 5 &

The optional wait command will then wait for all the jobs to finish.

Bash

sleep 10 & sleep 5 &
wait

Contribution

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

Translation

• Chinese | 简体中文
• Turkish | Türkçe
• Japanese | 日本語
• Russian | Русский
• Vietnamese | Tiếng Việt
• Spanish | Español

License