| README.md | ||
Table of Contents
- 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 (TODO) - Basic Shell Programming
2.1. Variables
2.3. String Substitution
2.4. Functions
2.5. Conditionals
2.6. Loops - Tricks
- Debugging
1. Basic Operations
a. export
Displays all environment variables and if you want to get detail of specific variable then use echo $VARIABLE_NAME
export
Example:
$ export
SHELL=/bin/zsh
AWS_HOME=/Users/adnanadnan/.aws
LANG=en_US.UTF-8
LC_CTYPE=en_US.UTF-8
LESS=-R
$ echo $SHELL
/usr/bin/zsh
b. whereis
Whereis search for executables, source files, and manual pages using a database built by system automatically.
whereis name
Example:
$ whereis php
/usr/bin/php
c. which
which search for executables in the directories specified by the environment variable PATH. This command will prints full path of the executable(s).
which program_name
Example:
$ which php
/c/xampp/php/php
d. clear
Clears content on window
1.1. File Operations
| ls | touch | cat | more | head | tail | mv | cp | rm | diff |
| chmod | gzip | gunzip | gzcat | lpr | lpq | lprm |
a. ls
Lists your files. It has a lot of options like -l lists files in 'long format', which contains the exact size of the file, who owns the file and 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
ls option
Example:
$ ls -al 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
b. touch
Creates or updates your file
touch filename
Example:
$ touch trick.md
c. 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
cat filename
cat file1 file2
cat file1 file2 > newcombinedfile
d. more
Shows the first part of a file (move with space and type q to quit)
more filename
e. head
Outputs the first 10 lines of file
head filename
f. tail
Outputs the last 10 lines of file. Use -f to output appended data as the file grows
tail filename
g. mv
Moves a file from one location to other
mv filename1 filename2
Where filename1 is the source path to the file and filename2 is the destination path to the file.
h. cp
Copies a file from one location to other
cp filename1 filename2
Where filename1 is the source path to the file and filename2 is the destination path to the file.
i. rm
Removes a file. But if you will apply this command on a directory directory, it will gives you an error
rm: directory: is a directory
So in order to remove directory you have to pass -rf to remove all the content of the directory recursively
rm filename
j. diff
Compares files, and shows where they differ
diff filename1 filename2
k. chmod
Lets you change the read, write, and execute permissions on your files
chmod -options filename
l. gzip
Compresses files
gzip filename
m. gunzip
Un-compresses files compressed by gzip
gunzip filename
n. gzcat
Lets you look at gzipped file without actually having to gunzip it
gzcat filename
o. lpr
Print the file
lpr filename
p. lpq
Check out the printer queue
lpq
Example:
$ lpq
Rank Owner Job File(s) Total Size
active adnanad 59 demo 399360 bytes
1st adnanad 60 (stdin) 0 bytes
q. lprm
Remove something from the printer queue
lprm jobnumber
1.2. Text Operations
| awk | grep | wc | sed | sort | uniq | cat | cut | echo | fmt |
| tr | nl | egrep | fgrep |
a. awk
Awk is most usefull command for handling text files. It operates on 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 specfies 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.
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. 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.
grep pattern filename
Example:
$ 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. Also -r can be used to search all files under the specified directory like
$ grep -r admin /etc/
And -w to search for words only. For more detail on grep, check following link.
c. wc
Tells you how many lines, words and characters there are in a file
wc filename
Example:
$ wc demo.txt
7459 15915 398400 demo.txt
Where 7459 is lines, 15915 is words and 398400 is characters.
d. sed
TODO
e. sort
TODO
f. uniq
TODO
g. cat
TODO
h. cut
TODO
i. echo
TODO
j. fmt
TODO
k. tr
TODO
l. nl
TODO
m. egrep
TODO
n. fgrep
TODO
1.3. Directory Operations
| mkdir | cd | pwd |
a. mkdir
Makes a new directory
mkdir dirname
b. cd
Moves you from one directory to other. If you just run
$ cd
Then it will moves you to home. Also this command accepts an optional dirname, which if provided will moves you to that directory.
cd dirname
c. pwd
Tells you in which directory you currently are
pwd
1.4. SSH, System Info & Network Operations
| ssh | whoami | passwd | quota | date | cal | uptime | w | finger | uname |
| man | df | du | last | ps | kill | killall | top | bg | fg |
| ping | whois | dig | wget |
a. ssh
ssh (SSH client) is a program for logging into a remote machine and for executing commands on a remote machine.
ssh user@host
This command also accepts an option -p that can to used to connect to specific port.
ssh -p port user@host
b. whoami
Return current logged in username
c. passwd
Allows the current logged user to change his password
d. quota
Shows what your disk quota is
quota -v
e. date
Shows the current date and time
f. cal
Shows the month's calendar
g. uptime
Shows current uptime
h. w
Displays who is online
i. finger
Displays information about user
finger username
j. uname
Shows kernel information
uname -a
k. man
Shows the manual for specified command
man command
l. df
Shows disk usage
m. du
Shows the disk usage of the files and directories in filename (du -s give only a total)
du filename
n. last
Lists your last logins of specified user
last yourUsername
o. ps
Lists your processes
ps -u yourusername
p. kill
Kills (ends) the processes with the ID you gave
kill PID
q. killall
Kill all processes with the name
killall processname
r. top
Displays your currently active processes
s. bg
Lists stopped or background jobs ; resume a stopped job in the background
t. fg
Brings the most recent job in the foreground.
u. ping
Pings host and outputs results
ping host
v. whois
Gets whois information for domain
whois domain
w. dig
Gets DNS information for domain
dig domain
x. wget
Downloads file
wget file
2. Basic Shell Programming
This is first line that you will in bash script files called shebang. The shebang line in any script determines the script's ability to be executed like an standalone executable without typing sh, bash, python, php etc beforehand in the terminal.
#!/bin/bash
2.1. Variables
Creating variable in bash is similar to other language. There are no data types. A variable in bash can contain a number, a character, a string of characters. You have no need to declare a variable, just assigning a value to its reference will create it.
Example:
str="hello world"
The above line creates a variable str and assigns "hello world" to it. Then the value of variable is retrieved by putting the $ in the beginning of variable name.
Example:
echo $str # hello world
Also like other languages bash has also arrays. An array is variable containing multiple values. There's no maximum limit on the size of array. Array 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:
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
One thing to note that if no index is supplied, array element 0 is assumed. To find out how many values there are in the array check 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
2.2 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
2.3. 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.
functname() {
shell commands
}
Example:
#!/bin/bash
function hello {
echo world!
}
hello
function say {
echo $1
}
say "hello world!"
When you will run 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 funtions, are treated in the same manner as arguments given to the script.
2.4. 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 # one of the statement 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
-r file # file exists and is not empty
-w file # your 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
2.5. Loops
There are three types of loops in bash. for, while and until.
Different for Syntax:
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:
while condition; do
statements
done
until Syntax:
until condition; do
statements
done
3. Tricks
set an alias
Open bash_profile by running following command nano ~/.bash_profile
alias dockerlogin='ssh www-data@adnan.local -p2222' # add your alias in .bash_profile
to quickly go to a specific directory
nano ~/.bashrc
export hotellogs="/workspace/hotel-api/storage/logs"
source ~/.bashrc cd hotellogs
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
- Open pull request with improvements
- Spread the word
License
