Day - 3 of internship at Aartronix

19) grep :  it is used to find pattern/string in files

examples:-

grep Name sample.txt

grep -v Name sample.txt

grep -n Name sample.txt grep -c Name sample.txt

grep -i name sample.txt

grep Name sample1.txt sample2.txt

echo grep -i error *.log

grep 5 sample.txt

grep -v 5 sample.txt

grep -r grep ~/Documents

grep -ri Error ~/Documents

• our sample.txt file:

MARKSHEET - Class 10A
| Roll No | Student Name | Math | English | Science | History | Total | Grade |
|---------|--------------|------|---------|---------|---------|-------|-------|
|    1    |  Aman Kumar  |  85  |    78   |    88   |   82    |  333  |   A   |
|    2    | Priya Sharma |  92  |    85   |    90   |   88    |  355  |   A+  |
|    3    | Rahul Singh  |  78  |    72   |    80   |   75    |  305  |   B   |
|    4    |  Neha Patel  |  88  |    90   |    86   |   91    |  355  |   A+  |
|    5    | Vikram Gupta |  75  |    68   |    72   |   70    |  285  |   B-  |
|    6    | Anjali Verma |  95  |    92   |    94   |   89    |  370  |   A+  |
|    7    |  Rohan Desai |  82  |    80   |    81   |   79    |  322  |   A   |
|    8    |   Zara Khan  |  90  |    88   |    89   |   87    |  354  |   A+  |

    25) ls :- to list files and directories in current directory

        -l ---> shows permissions and other details

    26) pwd : prints working directory

    

    27) cd : - change directory 

    

    28) mkdir :- make directory ; mkdir name_of_dir

• For multiple directory 
• mkdir dir1 dir2 dir3 (here dir can be replaced by any string)
• mkdir dir{1,2,3}
• mkdir {1,2,3}dir
• mkdir dir{1..7}

    29) rmdir :- remove empty directory ; rmdir name_of_dir

• For multiple directory 
• rmdir dir1 dir2 dir3 (here dir can be replaced by any string)
• rmdir dir{1,2,3}
• rmdir {1,2,3}dir
• rmdir dir{1..7}

    30) cp/mv :-  copy/move ; cp/mv <from_file>  <to_file>

• can be used on multiple files:
• mv/cp file{1..8} file{1..8}.txt

    31) rm :- remove file; rm [options]  <file>

• to remove directories completely use -r 
• using -i , it would ask before removing any file or directory everytime.

  32)touch:- The touch command in Linux creates an empty file or updates the timestamp of an existing file. 

  33)clear :- it clears the console/terminal.

 

Scripting:

1. Script to make directory and files.
• banner DIRECTORY MAKER SCRIPT

  echo Starting directory creation script...

  i=1

  ls

  while

  [ $i -lt 5 ]

  do

  echo creating dir$i

  mkdir dir$i

  cd dir$i

  echo This is file in directory $i. > file$i.txt

  cd ..

  ((i++))

  done

  ls

  echo script execution completed
2. Script To make and remove directory  but preserve file.
• banner DIRECTORY REMOVER SCRIPT

  echo Starting directory remover script...

  i=1

  ls

  while

  [ $i -lt 5 ]

  do

  cd dir$i

  echo Moving files in directory$i.

  mv * ~/Documents/Scripts/

  cd ..

  echo Removing dir $i.

  rm -r dir$i

  ((i++))

  done

  ls

  echo script execution completed

SHELL

• The Shell -  To  communicate and work with kernel user needs an interface that can be graphical or text based.
• The Shell Families
• Bourne Shell
• Korn Shell(Ksh)
• Csh & TCsh
• COMMAND.COM(MS-DOS)
• All Shell follow same 4 steps process:
• Read a command line.
• Parse and interpret it.
• Invoke the execution of the command line.
• Go to step 1.

• Shell Prompt
• ways to get shell access:
• Terminal - By running terminal.
• SSH - By logging in into remote server.
• Console - By logging into system.
• some useful commands to know about your shell:
• echo $SHELL
• cat /etc/shells
• $env

• Environment Variables
• $HOME - 
• $IFS
• $LANG
• $MAIL
• $PATH
• $PS1
• $PS2
• $SHELL
• $TERM

• Shell Scripting
• Well generally we give command to shell and it takes it to kernel but what if we want to this process, we use shell scripting, Shell Script is a text file containing commands we run in a shell environment. 

• Why shell Scripting
• Creating your own power tools/utilities.
• Automating Command input and output.
• Customizing administrative tasks.(Well you don't enjoy write same commands do you, do you?)
• Creating simple applications.

• The bash shell - The bourne Again shell.
• It have two types of commands:
• internal - inbuilt commands.
• external - imported binary libraries stored in /bin

• The shell programming environment
• Two ways to make shell scripts:
• use #! /bin/sh as first line of shell script.
• use sh -f filename.sh command after writing script.

• Shebang - It is the line which indicates an interpreter to execute the shell script.

• Shell comments - They are comments like in any programming language and start with "#".