Hello everyone !!!

Myself Smaran Sandep Dambe , and I am back with my next blog . So this is gonna be my 7 blog which is held in DBATU by Master Pranav Jambare . In this session the points that are covered are listed below :

1 . Filters

2 . Shell scripting introduction

3 . if-else statement

So let's start our blog !!!

1 . Filters :

In UNIX/Linux, filters are the set of commands that take input from standard input stream i.e. stdin, perform some operations and write output to standard output stream i.e. stdout. The stdin and stdout can be managed as per preferences using redirection and pipes. Common filter commands are: grep, more, sort.The FILTER command is used to append to or replace the current path name filter. If the current display is a personal list, then the filter can only be replaced.

- Linux Filter Commands with syntax and examples :

Sort :

Syntax

    #To sort content of file by alphabetical order
    sort <filename>
    #To sort the content of file by reverse alphabetical order
    sort -r <filename>
    #To sort the numeric content of the file
    sort -n <filename>
    #To sort the month names in the file
    sort -M <filename>

Example :

    #Lets assume we have TestFile with normal unsorted content
    #TestFile1 with numerical content
    #And TestFile2 with month names
    sort TestFile

    sort -r TestFile

    sort -n TestFile1

    sort -M TestFile2

Tail :

Syntax

    #To get the dynamic output
    tail -f <filename>
    #To get the content on the particular line of the file
    tail -<line number> <filename>
    #To display specific bytes of content of the file
    tail -c <number of bytes> <filename>
    #To display content of multiple files
    tail <file1> <file2>

Example :

    tail -f TestFile

    tail -5 TestFile

    tail -c 200 TestFile

    tail TestFile TestFile1

Head :

Syntax

    #To show specific number of lines from the content of the file
    head -n <number of lines> <filename>
    #To display the specific number of bytes of content of the file
    head -c <number of bytes> <filename>
    #To show the content of multiple files
    head <file1> <file2>
    #To show merged content of multiple files
    head -q <file1> <file2>
    #To show the content of the file preceded by it's file name
    head -v <filename>

Example :

    head -n 5 TestFile

    head -c 500 TestFile

    head TestFile TestFile1

    head -q TestFile TestFile1

    head -v TestFile

WC (word count) :

Syntax

    #To show the number of lines in the file
    wc -l <filename>
    #To show characters(letters) of the content in the file
    wc -m <filename>
    #To show number of words of the content in the file
    wc -w <filename>
    #To show the specific number of bytes of content of the file
    wc -c <filename>

Example :

    wc -l TestFile

    wc -m TestFile

    wc -w TestFile

    wc -c TestFile

uniq :

Syntax

    #To show the count of repeated lines in the file
    uniq -c <filename>
    #To print repeated lines in the file
    uniq -d <filename>
    #To
    uniq -D <filename>
    #To show unique lines in the content of the file
    uniq -u <filename>

Example :

    uniq -c TestFile

    uniq -d TestFile

    uniq -D TestFile

    uniq -u TestFile

comm :

  #Syntax - It shows the common content between two files
  comm <file1> <file2> 
  #Example
  comm TestFile TestFile1

diff :

  #Syntax - It shows the different(uncommon) content between two files
  diff <file1> <file2>
  #Example
  diff TestFile TestFile1

grep :

Syntax

    #To search word - case insensative
    grep <"word to be searced"> -i <filename>
    #To print only the matched parts of a matching line,with each such part on a separate output line
    grep <"word to be searched"> -o <filename>
    #To prints output after the result
    grep <"word to be searched"> -A <filename>
    #To prints output before the result
    grep <"word to be searched"> -B <filename>
    #To prints output after and before the result
    grep <"word to be searched"> -C <filename>
    #To print the count of the word in the file
    grep <"word to be searched"> -c <filename>
    #To print the matched word in the file
    grep <"word to be searched"> -w <filename>
    #To print multiple matched words
    grep <"word to be searched"> -e <filename>
    #To print the matched lines with line numbers
    grep <"word to be searched"> -n <filename>

Example :

    grep "word" -i TestFile

    grep "word" -o TestFile

    grep "word" -A TestFile

    grep "word" -B TestFile

    grep "word" -C TestFile

    grep "word" -c TestFile

    grep "word" -w TestFile

    grep "word" -e TestFile

    grep "word" -n TestFile

awk :

Syntax

    #To print the content of the file
    awk '{print}' <filename>
    #To print the lines which matches the given word in the file
    awk '/word/' '{print}' <filename>
    #To print the specific words of the lines in the file
    awk '{print $<line number>, $<line number>}' <filename>
    #To print the last line of the file
    awk '{print $NF}' <filename>
    #To print the particular words of particular lines of the file
    awk 'NR==<number of word>, NR==<number of word>' '{print $<number of line>, $<number of line>}' <filename>

Example :

    awk '{print}' TestFile

    awk '/computer/' '{print}' TestFile

    awk '{print $1, $3}' TestFile

    awk '{print $NF}' TestFile

    awk 'NR==1, NR==3' '{print $1, $3}' TestFile

cut :

#Syntax - Deluminator
cut -d '<deluminator>' -f <filename>
#Example
cut -d '-' -f TestFile

sed :

Syntax

    #To replace the word by occurance
    sed 's/<word to be replaced>/<replaced with>/<occurance>' <filename>
    #To replace the word globally
    sed 's/<word to be replaced>/<replaced with>/g' <filename>
    #To replace the word on the specific line
    sed '<line number> s/<word to be replaced>/<replaced with>/ ' <filename>
    #To delete the last line
    sed '$d' <filename>
    #To delete the particular lines
    sed '<number of line>d' <filename>
    #To delete the word matching lines
    sed '/<word to be matched>/d' <filename>

Example :

    sed 's/desktop/laptop/2' TestFile

    sed 's/desktop/laptop/g' TestFile

    sed '3 s/desktop/latop/ ' TestFile

    sed '$d' TestFile

    sed '2d' TestFile

    sed '/computer/d' TestFile

2 . Shell Scripting Introduction :

A shell script is a computer program designed to be run by a Unix shell, a command-line interpreter. The various dialects of shell scripts are considered to be scripting languages. Typical operations performed by shell scripts include file manipulation, program execution, and printing text.Shell scripting is not a single language but, because it uses some natural language commands, it's easy to learn, even without a programming background. However, each shell scripting dialect is considered a language, and if you plan more complex activities, shells take a lot of practice.They are used to get routine backups by admins. They are easier to write and debug than other programming languages like C or C++. We can transfer the shell script to other UNIX and similar operating systems and execute. Shell scripts are also used to monitor systems regularly.

You can also set certain scripts to execute on startup such as showing a particular message on launching a new session or setting certain environment variables.

1 . Bash Scripts :

Bash scripting is a subset of shell scripting. Shell scripting is a method to automate tasks as a collection of commands. The bash script is one form of shell script. Shells may be one of Korn, C shell, Bourne, Bash, etc.Bash as a scripting language. To create a bash script, you place #!/bin/bash at the top of the file. To execute the script from the current directory, you can run ./scriptname and pass any parameters you wish. When the shell executes a script, it finds the #!/path/to/interpreter .

2 . Shebang :

On Linux, a shebang (#!) is a special line at the beginning of a script that tells the operating system which interpreter to use when executing the script. This line, also known as a hashbang, shabang or "sharp-exclamation", is the first line of a dash and starts with "#!" followed by the path to interpreter.#!/bin/bash is a sequence of characters (#!) called shebang and is used to tell the Linux OS which interpreter to use to parse the rest of the file. You will always see #!/bin/bash or #!/usr/bin/env bash as the first line when writing or reading bash scripts

- ```
         #Syntax
         #!/bin/bash
```

Creating the script :

Create a file with .sh extension :

COPY
```
    vim TestScript.sh
```

Modify the same file :

    #Syntax
    #!/bin/bash/
    <command>

    #Example
    #!/bin/bash/
    cd /tmp/
    touch testfile
    ls -l

Then save and exit.

Run the script :

    #Run by giving the execute permissions
    chmod u+x TestScript.sh
    ./TestScript.sh

    #Run without giving execute permissions
    bash TestScript.sh

Variable declaration :

Temporary variables :

    #Syntax
    <variable name>=<content>
    #Example
    name=Shreyas

Permanent variables :

    #Navigate through /etc/bashrc file 
    vim /etc/bashrc
    #Add your variables here
    #Syntax
    <variable name>=<content>
    #Example
    name=Shreyas

Important Point :

Operator	Respective Option
\>	-gt
<	-lt
&&	-a
		-o

3 . if-else statement

Simple If :

Syntax :

    if [expression]
    then
        statement
    fi

Example :

    if [ ${A} -gt ${B} ]
    then
        echo "${A} is greater than ${B}"
    fi

If-Else :

Syntax :

    if [expression]
    then
        statement
    else 
        statement
    fi

Example :

    if [ ${A} -gt ${B} ]
    then
        echo "${A} is greater than ${B}"
    else 
        echo "${B} is greater than ${A}"
    fi

Multiple If :

Syntax :

    if [expression]
    then
        Statement
    elif [expression]
    then
        Statement
    elif [expression]
    then
        Statement
    else
        Statement
    fi

Example :

    if [ ${age} -gt 0 -a ${age} -lt 15 ]
    then
        echo "You are a kid"
    elif [ ${age} -gt 15 -a ${age} -lt 18 ]
    then
        echo "You are a teen"
    else
        echo "Invalid age"
    fi

Nested - If :

Syntax :

    if [expression]
    then
        Statement
        if [expression]
        then
            Statement
        else
            Statement
        fi
    else
        Statement
    fi

Example :

    if [ ${Fname} == Shreyas ]
    then
        echo "First name matched"
        if [ ${Sname} == Limaye ]
        then
            echo "First name and Surname both matched"
        else
            echo "First name matched but surname doesn't matched"
        fi
    else
        echo "First name doesn't matched stopped execution"
    fi

So this was all about what I learnt in session 7 of Linux . This session was so good because all the practical knowledge which was given by Pranav Jambare sir was up yo mark...... So please read it ..... and like it!!!!!!

Extreming the globe of Linux

1 . Filters

2 . Shell scripting introduction

3 . if-else statement

1 . Filters :

- Linux Filter Commands with syntax and examples :

2 . Shell Scripting Introduction :

1 . Bash Scripts :

2 . Shebang :

3 . if-else statement

Subscribe to my newsletter

Smaran Sandeep Dambe

Smaran Sandeep Dambe