Using Pipes :
There are times when you need to send the output of one command to the input of another command.
Engr. Abhishek Roshan
Basic Script Building – Redirecting Input and Output
Redirecting Input and Output
At times, you may find it beneficial to store the results of a command rather than simply viewing them on the screen. The bash shell offers various operators for redirecting command output to different destinations, such as files. Additionally, redirection can manage input, enabling you to redirect a file to a command for processing. This section will outline the steps required to implement redirection in shell scripts.
Output Redirection:
The most basic type of redirection is sending output from a command to a file. The bash shell uses the greater-than symbol (>) for this:
command > outputfile
Sometime, instead of of overwriting the file content,you may need to append output from a command to existing file.For Example, if you’re creating a log fileto document an action on the system.In this stituation, you can use the double greater-than symbol (>>) to append data:
[root@engrabhishekroshan scripts]# date;who >> outputredirection.txt
Sun Apr 7 01:08:18 AM IST 2024
[root@engrabhishekroshan scripts]# cat outputredirection.txt
root pts/0 2024-04-06 18:06 (192.168.72.1)
[root@engrabhishekroshan scripts]#
Input Redirection:
Input redirection is the opposite of output redirection. Instead of taking the output of a command and redirecting it to a file, input redirection takes the content of a file and redirects it to a command.
Basic Script Building – Using Variables
Basic Script Building - Using Variables
Environment Variables
Basic Script Building – Displaying Messages
Basic Script Building – Displaying Messages
Basic Script Building – Creating a Script File
Basic Script Building - Creating a Script File
Script : Is a collection of Linux commands only, When creating a shell script file, you should mention the shell you are using in the first line of the file. Format for this is
#!/bin/bash
Basic Script Building – Using Multiple Commands
Using Multiple Commands
In Linux so far you have seen how to use the command-line Interface (CLI). For Example: if you run “date” command we get the out put date and time
[root@engrabhishekroshan /]# date
Wed Jan 31 06:15:38 PM IST 2024
[root@engrabhishekroshan /]#
For Example: If you run “who” command ,we get the output as which all users logged into the system.
[root@engrabhishekroshan /]# who
root pts/0 2024-01-26 10:16 (192.168.72.1)
[root@engrabhishekroshan /]#
Using multiple Commands we can combined these two commands into a single commands by using semicolon ;
[root@engrabhishekroshan /]# date;who
Wed Jan 31 06:22:05 PM IST 2024
root pts/0 2024-01-26 10:16 (192.168.72.1)
[root@engrabhishekroshan /]#
Linux Shell Scripting Beginner To Expert Course //Course Content // Topic -1
| Topic | Sub-Topic |
| Shell Scripting Basics | |
| Using Multiple commands | |
| Creating a script file | |
| Displaying Messages | |
| Using Variables | |
| Redirecting Input & Output | |
| Employing Pipes | |
| Performing Maths | |
| Exiting the Script | |
| Practical – Lab | |
| Using Structured Commands | |
| Working with the if-then statement | |
| Exploring the if-then Statement | |
| Nesting file | |
| Trying the test Command | |
| Considering Compound Testing | |
| Working with Advanced if-then feature | |
| Considering the case Command | |
| Practical Lab | |
| More Structured Commands | |
| Looking at for command | |
| Trying the C-style for command | |
| Exploring the While Command | |
| Using the until command | |
| nesting Loop | |
| Looping on file Data | |
| Controlling the Loop | |
| Processing the Output of a Loop | |
| Practical Lab | |
| Handling User Input | |
| Passing Parameter | |
| Using Special Parameter Variable | |
| Being Shifty | |
| Working with Option | |
| Standardizing Option | |
| Getting user Input | |
| Practical Lab | |
| Presenting Data | |
| Understanding Input and Output | |
| Redirecting output in Scripts | |
| Redirecting Input in Scripts | |
| Creating Your own redirections | |
| Listing Open file Descriptors | |
| Supressing Command Output | |
| Using Temporary Files | |
| Logging Messages | |
| Practical lab | |
| Script Control | |
| Handling Signals | |
| Running Scripts in Background Mode | |
| Running Scripts without a hang-Up | |
| Controlling the Job | |
| Being Nice | |
| Running like Clockwork | |
| Practical Lab |
AWS 300 + Realtime scenario based Interview questions and answers explained in detail | Part – 1
Question 1. List the components to build Amazon VPC ?
Answer:
Linux 100 + Realtime Scenario Based Interview Questions and Answers Explained in Detail | Part – 2
Question 11. What is NFS ? How to configure it ? What port no it does use ?
Answer:
- To configure NFS we need to cionfigure NFS Server and NFS Client.
- Steps to configure NFS Server.
- a)Install nfs-util package.
- b)Create a directory or directory on a partition and some data on it.
- c)Now export the directory by editing /etc/exports file and using exportfs command.
- d)Restart the service and make is permanent in /etc/fstab file.
- Steps to configure NFS client.
- a)check and install the NFS package if not installed.
- b)start the NFS service
- c)check which directory is exported for this machine using showmount command
- d)Make a directory and mount the NFS dir over it.
- e) Add some data to it and check the same is updated on server side.
- Port No -2049
Linux 100 + Realtime Scenario Based Interview Questions and Answers Explained in Detail | Part – 1
Question 1. How to set a username and password to never expires ?
Answer: chage -M -1 krishna
Question 2. Why /etc/passwd and /etc/shadow file cannot be merged into one file ?
Answer:
- The existence of the two files is a consequence of that /etc/passwd is a text file that can be read by other applications (as finger, ident or ls for example), so an attacker could gain access to the information of the file that included the hashed password.
- To increase security, the hashed password that used to be in the file was moved to other file called /etc/shadow that is accessible only by root
Question 3 : How to list, all the files opened by particular PID ?
Answer:
- lsof –p PID
- Count number of files & processes
Question 4: We are unable to unmount the file system. What are the reason behind it ?
Answer:
- #you are in the same directory pwd ,
- #some users are present in the directory and using its content fuser -cu /dev/sda,
- #some of the files are open in the directory lsof /dev/sda7
Question 5 : What could be the reason if server take more time after reboot ?
Answer:
- filesystem got corrupt and its ext2,ext2 is not having journaling feature.
Question 6 : we are trying to create the file under any partition but we are getting permission denied alert. What could be the reason? However,
no space issue and no permission issue?
Answer :
- I am running out of inode
- Sometimes, df command reports that there is enough free space but system claims file-system is full.
- You need to check for the inode which identifies the file and its attributes on a file systems using the following command:
- $ df -i
- $ df -i /ftpusers/
- Sample outputs:
- Filesystem Inodes IUsed IFree IUse% Mounted on
- /dev/sda8 6250496 11568 6238928 1% /ftpusers
- So /ftpusers has 62,50,496 total inodes but only 11,568 are used. You are free to create another 62,38,928 files on /ftpusers partition.
- If 100% of your inodes are used, try the following options:
- Find unwanted files and delete or move to another server.
Find unwanted large files and delete or move to another server