Hey Guys, here is another blog after the roller coaster ride of life... The continuation of the workshop series... Hope you love the blog from a naive blogger... Let's see what I have added to my mind palace...

Filters

Filters are programs that take plain text(either stored in a file or produced by another program) as standard input, transform it into a meaningful format, and then return it as standard output. Linux has a number of filters. Some of the most commonly used filters are explained below -

Sort -

Commands are as follows

 sort [filename] #This sorts by alphabetical order
 sort -r [filename] #This sorts by reverse alphabetical order
 sort -n [filename] #This sorts the numeric content of the file
 sort -M [filename] #This sorts the month names in the file

Tail -

Commands are as follows

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

Head -

Commands are as follows

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

WC (Word Count) -

Commands are as follows

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

Uniq -

Commands are as follows

 uniq -c [filename] #To show the count of repeated lines in the file
 uniq -d [filename] #To print repeated lines in the file
 uniq -D [filename] #To display duplicate lines in sorted file
 uniq -u [filename] #To show unique lines in the content of the file

Comm -

Commands are as follows

 #Syntax 
 comm [file1] [file2] #It shows the common content between two files

Diff -

Commands are as follows

 #Syntax 
 diff [file1] [file2] #It shows the different content between two files

grep -

Commands are as follows

 grep ["word"] -i [filename] #To search word - case insensative.
 grep ["word"] -o [filename] #To print only the matched parts of a matching line.
 grep ["word"] -A [filename] #To prints output after the result.
 grep ["word"] -B [filename] #To prints output before the result.
 grep ["word"] -C [filename] #To prints output after and before the result.
 grep ["word"] -c [filename] #To print the count of the word in the file.
 grep ["word"] -w [filename] #To print the matched word in the file.
 grep ["word"] -e [filename] #To print multiple matched words.
 grep ["word"] -n [filename] #To print the matched lines with line numbers.

awk -

Commands are as follows

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

cut -

Commands are as follows

#Syntax 
cut -d '<deluminator>' -f <filename>

sed -

Commands are as follows

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

Shell Scripting

Shell scripting is an important part of process automation in Linux. Scripting helps us write a sequence of commands in a file and then execute them. This saves us time because we don't have to write certain commands again and again. We can perform daily tasks efficiently and even schedule them for automatic execution. We can schedule tasks at startups and many more...

Bash Scripts -

A bash script is a series of commands written in a file. These are read and executed by the bash program. The program executes line by line. By naming conventions, bash scripts end with a .sh. Certainly, bash scripts can run perfectly fine without the sh extension.

Shebang -

Scripts are also identified with a shebang. Shebang is a combination of bash# and bang! followed the bash shell path. This is the first line of the script. Shebang tells the shell to execute it via bash shell. Shebang is simply an absolute path to the bash interpreter.

#Syntax
#!/bin/bash

Creating the script -

# Create a file with .sh extension 
vim Agenda.sh

Modify the same file -

#Syntax
#!/bin/bash/
[command]

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

#Save and exit.

Run the script -

#Run by giving the execute permissions
chmod u+x Agenda.sh
./Agenda.sh
#Run without giving execute permissions
bash Agenda.sh

Variable declaration -

Temporary variables
```
  #Syntax
  <variable name>=<content>
```
Permanent variables

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

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 13 ]
  then
      echo "You are a kid"
  elif [ ${age} -gt 13 -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} == Kakashi]
  then
      echo "First name matched"
      if [ ${Sname} == Hatake ]
      then
          echo "First name and Clanname both matched"
      else
          echo "First name matched but Clanname doesn't matched"
      fi
  else
      echo "First name doesn't matched stopped execution"
  fi

Hope you loved the blog from a naive blogger...

Into the Linux-verse

Table of contents

Filters

Shell Scripting

If-Else Statement

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Arfat Kadvekar

Arfat Kadvekar