Unix Commands

Category : Unix | Sub Category : Unix | By Prasad Bonam Last updated: 2024-03-02 03:59:11 Viewed : 104

Unix commands are powerful tools for interacting with the Unix operating system and its variants like Linux. Here are explanations for some advanced Unix commands:

1. grep: This command is used to search text or files for lines that match a specific pattern. It is incredibly powerful when combined with regular expressions. For example:

   bashCopy code
   grep "pattern" file.txt
   

2. find: Used to search for files in a directory hierarchy. It allows you to search based on various criteria like name, type, size, etc.

   bashCopy code
   find /path/to/search -name "filename"
   

3. awk: A versatile programming language mainly used for pattern scanning and processing. It is often used for data extraction and reporting.

   bashCopy code
   awk `{print $2}` file.txt
   

4. sed: Stands for stream editor. It is used for filtering and transforming text, typically used in conjunction with piping.

   bashCopy code
   sed `s/old_pattern/new_pattern/g` file.txt
   

5. xargs: Used to build and execute command lines from standard input. It is often used with find, grep, and other commands for efficient command execution.

   bashCopy code
   find . -type f -name "*.txt" | xargs grep "pattern"
   

6. rsync: A powerful utility for syncing files and directories between two locations. It is commonly used for backups and mirroring.

   bashCopy code
   rsync -avz source/ destination/
   

7. wget: Used for downloading files from the internet via HTTP, HTTPS, and FTP protocols.

   bashCopy code
   wget http://example.com/file.txt
   

8. curl: Another tool for transferring data from or to a server. It supports various protocols and can be used for testing APIs, downloading files, etc.

   bashCopy code
   curl -O http://example.com/file.txt
   

9. tar: Stands for tape archive. It is used for archiving files and directories into a single file (often called a "tarball") and optionally compressing it.

   bashCopy code
   tar -cvzf archive.tar.gz /path/to/directory
   

10. chmod: Used to change permissions of files and directories.

    bashCopy code
    chmod 755 file.sh
    

These commands, along with many others, form the backbone of Unix-like operating systems, offering administrators and users powerful tools for managing and manipulating files, processes, and system configurations.

awk `{print $2}` file.txt with example

Let`s say you have a file called data.txt with the following content:

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Name Age Gender
John 25 Male
Alice 30 Female
Bob 22 Male

If you want to extract only the second column (which contains ages), you can use the awk command like this:

bashCopy code
awk `{print $2}` data.txt

Output:

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Age
25
30
22

Explanation:

• awk is invoked with the single quotes enclosing {print $2}. This is an awk program that tells awk to print the second field of each line.
• file.txt is provided as input to awk.
• For each line of file.txt, awk splits the line into fields based on whitespace (by default). $2 refers to the second field in each line.
• awk then prints the second field of each line, resulting in the output you see above.

sed `s/old_pattern/new_pattern/g` file.tx with example:

The sed command is used for text manipulation and stands for "stream editor." Lets consider an example with a file called data.txt containing the following text:

vbnetCopy code
Hello world
This is a sample text.
Replace old_pattern with new_pattern.

If you want to replace occurrences of "sample" with "example" in this file, you can use sed like this:

bashCopy code
sed  `s/sample/example/g` data.txt

Output:

vbnetCopy code
Hello world
This is a example text.
Replace old_pattern with new_pattern.

Explanation:

• sed is invoked with the single quotes enclosing the s/sample/example/g command.
• s indicates a substitution.
• sample is the old pattern that you want to replace.
• example is the new pattern that you want to replace it with.
• g stands for global, meaning it will replace all occurrences in each line. If you omit g, sed will only replace the first occurrence in each line.

So, in this example, sed replaces all occurrences of "sample" with "example" in the data.txt file and prints the modified text to the standard output.