Day-01 shell scripting
First, we need to install net-tools to use ifconfig and nslookup.
sudo apt install net-tools -y && sudo apt install unzip -y && sudo apt install jq -y
Explanation:
. sudo apt install net-tools -y: Installs net-tools (for ifconfig). . sudo apt install unzip -y: Installs unzip (for extracting ZIP files). . sudo apt install jq -y: Installs jq (a tool for processing JSON).
for loop
#!/bin/bash
for i in {1..10}; do echo $(date) done
Explanation:
. for i in {1..10}; do: This initializes a loop that will run 10 times. . echo $(date): This prints the current date and time for each iteration. . done: This marks the end of the loop.
#!/bin/bash
for i in {1..10}; do echo $(date) | awk ‘{print $1}’ sleep 1 done
Explanation:
. for i in {1..10}; do: This loop will iterate 10 times. . echo $(date) | awk ‘{print $1}’: This command prints the first field (the day of the week) from the date output. . sleep 1: This pauses the loop for 1 second after each iteration. . done: This marks the end of the loop.
#!/bin/bash
for i in {1..10}; do echo $(date) | awk ‘{print $1, $2, $3, $4}’ sleep 1 done
Explanation:
. for i in {1..10}; do: This starts a loop that will run 10 times. . echo $(date) | awk ‘{print $1, $2, $3, $4}’: This prints the first four fields of the date output: . $1: Day of the week . $2: Month . $3: Day of the month . $4: Time . sleep 1: This pauses the loop for 1 second after each iteration. . done: This indicates the end of the loop.
Variables
Example: Simple Variable
#!/bin/bash
Define a variable
name=”Surya Prasad”
Access and print the variable
echo $name
diff b/w Single Quotes and Double Quotes
. Single Quotes (‘): Treat everything as a literal string. . Double Quotes (“): Allow variable expansion and interpret special characters.
Example: Single Quotes
#!/bin/bash
name=”Surya Prasad” fullname=’Mokadi — $name’
echo “$fullname”
Explanation:
.Variable Assignment: . name=”Surya Prasad”: Assigns the value Surya Prasad to name. . fullname=’Mokadi — $name’: The $name is treated literally as the string $name, not its value. . Printing the Value: . echo “$fullname”: This will print Mokadi — $name.
Example: Double Quotes
#!/bin/bash
name=”Surya Prasad” fullname=”Mokadi — $name” echo “$fullname”
Explanation:
.Variable Assignment: . name=”Surya Prasad”: Assigns the value Surya Prasad to the variable name. . fullname=”Mokadi — $name”: Uses double quotes to allow variable expansion, resulting in fullname being Mokadi — Surya Prasad. . Printing the Value: . echo “$fullname”: This will print Mokadi — Surya Prasad.
cut command
aws s3 ls | cut -d “ “ -f1 aws s3 ls | cut -d “ “ -f1 > text.logs
Explanation:
.aws s3 ls: . This command lists the contents of an S3 bucket, showing details such as the last modified date, size, and file names. . | (Pipe): . This operator takes the output of the command on the left (aws s3 ls) and sends it as input to the command on the right (cut). . cut -d “ “ -f2: . cut: A command used to extract sections from each line of input. . -d “ “: Specifies that a space is the delimiter for separating fields. . -f2: Indicates that you want to extract the second field from each line of the output. . > text.logs: will store all the extracted timestamps from the S3 listing into the file. . >> text.logs: If the file already exists, the new timestamps will be added to the end of the file without overwriting the existing content.
Note
. The command aws s3 ls | cut -d “ “ -f1,f2,f3, cut does not support reversing fields directly. Instead, you can use awk, which allows you to control the output order more flexibly.
awk command
. Here’s how to use awk to reverse the fields: aws s3 ls | awk ‘{print $3, $2, $1}’
Explanation:
. awk ‘{print $3, $2, $1}’: Prints the fields in reverse order: . $3: File size . $2: Last modified time . $1: Last modified date
grep command
Explanation:
. | grep -i www.: . grep: This command searches for patterns in text. . -i: Makes the search case-insensitive, meaning it will match “www”, “Www”, “WWW”, etc. . www.: The pattern to search for in the filenames. It will match any filenames containing “www”.
. If wanted see only the particular entries with “www.logs,"
Explanation:
. | grep -E www[.]: . grep: Searches for lines that match a specified pattern. . -E: Enables extended regular expressions, allowing for more complex patterns. However, in this case, just using www. is sufficient. .www[.]: Matches any filenames containing “www.” The brackets around the dot (.) indicate that the dot is treated as a literal character rather than a special regex character. .”www[-]”: Matches any lines containing “www-” (the — is treated as a literal character).
Three text editors
. Vi, Vim, and Nano
Create a new script file
nano myscript.sh #!/bin/bash echo “Hello, World!”
. you need to give the permissions to the above file chmod +x myscript.sh
Run your script
./myscript.sh
set -x command
set -x command mainly using to check the debugging purposes.
Enable Debugging:
#!/bin/bash set -x # Enable debugging
Disable Debugging:
set +x # Disable debugging
Output
bash script.sh
- grep -E ‘www[.]’
- cut -d ‘’ -f3
- aws s3 ls
