> ## Documentation Index > Fetch the complete documentation index at: https://notes.kodekloud.com/llms.txt > Use this file to discover all available pages before exploring further. # sed print > This guide teaches how to use seds print script to selectively display lines and control output in command-line workflows. sed is a powerful **stream editor** for transforming text on the command line. In this guide, you'll learn how to use the `p` (print) script to display lines selectively, control automatic output, and integrate sed into complex pipelines. Whether you're filtering log files or extracting specific records, mastering sed's I/O model is essential for efficient command-line workflows. ## Unix I/O Model | I/O Type | Description | Example | | | | ----------------- | -------------------------------------------------- | ---------------------------------------------- | ------------- | --------- | | Default Output | Commands write to the terminal by default | `ls` | | | | Default Input | Commands read from files or stdin when unspecified | `grep "pattern" file.txt` | | | | Pipes (\` | \`) | Passes one command's output as another's input | \`echo "data" | sed 'p'\` | | Interactive Input | Reads from keyboard until EOF or termination | `sed 'p'` | | | ## sed's Default Behavior By default, sed processes text from **stdin** or listed files and writes each line to **stdout**, applying any provided scripts. Typing: ```bash theme={null} sed 'p' ``` reads from stdin and applies the `p` (print) script to every line. Example: ```bash theme={null} echo "Hello from sed" | sed 'p' ``` Output: ```bash theme={null} Hello from sed Hello from sed ``` Explanation: 1. sed reads each line into the *pattern space*. 2. The `p` script prints it immediately. 3. Without disabling automatic printing, sed outputs the line again after processing. ### Syntax Overview ```text theme={null} sed [OPTION]... {script-only-if-no-other-script} [input-file]... ``` ![The image shows a command-line syntax for the sed command, specifically highlighting the use of the print (p) script.](https://kodekloud.com/kk-media/image/upload/v1752868674/notes-assets/images/Advanced-Bash-Scripting-sed-print/sed-command-line-print-syntax.jpg) ## Using sed with Pipes and Files ### Piping Input ```bash theme={null} echo "This line prints twice" | sed 'p' ``` Output: ```text theme={null} This line prints twice This line prints twice ``` ### Reading from a File ```bash theme={null} echo "File line example" > sample.txt sed 'p' sample.txt ``` Output: ```text theme={null} File line example File line example ``` In this case, `sample.txt` replaces stdin as sed's input source. ## Selecting Specific Lines sed supports *addresses* (such as line numbers) to target scripts. ```bash theme={null} # Create a sample file echo "first line" > file_sample.txt echo "second line" >> file_sample.txt echo "third line" >> file_sample.txt # Print only the second line twice sed '2p' file_sample.txt ``` Output: ```text theme={null} first line second line second line third line ``` Explanation: * Line 2 matches `2p`, so it's printed by the script and then automatically once more. Use single quotes (`'`) around sed scripts to prevent the shell from interpreting special characters. ## Suppressing Automatic Printing To output only the lines you explicitly match, use the `-n` option. ```bash theme={null} sed -n '2p' file_sample.txt ``` Output: ```text theme={null} second line ``` Forgetting `-n` can lead to duplicate lines when using print scripts. ## Real-World Example: Filtering Command Output Extract the third line from the `df -h` display: ```bash theme={null} df -h ``` ```text theme={null} Filesystem Size Used Avail Use% Mounted on /dev/root 7.7G 2.9G 4.9G 38% / devtmpfs 486M 0 486M 0% /dev tmpfs 490M 0 490M 0% /dev/shm ... ``` Apply sed: ```bash theme={null} df -h | sed -n '3p' ``` Result: ```text theme={null} tmpfs 490M 0 490M 0% /dev/shm ``` ## Working with a Data File Consider an `employees.txt` file with pipe-delimited records: ![The image shows a text file named "employees.txt" containing a list of employees with details such as name, department, job title, email, and salary.](https://kodekloud.com/kk-media/image/upload/v1752868675/notes-assets/images/Advanced-Bash-Scripting-sed-print/employees-list-details-text-file.jpg) | Field No. | Field Name | Description | | --------- | ------------- | --------------------- | | 1 | Record Number | Unique employee ID | | 2 | First Name | Employee's first name | | 3 | Last Name | Employee's last name | | 4 | Department | Department name | | 5 | Job Title | Position held | | 6 | Email | Company email address | | 7 | Salary | Annual salary in USD | To print the fifth record only: ```bash theme={null} sed -n '5p' employees.txt ``` Output: ```text theme={null} 5|Feng|Lin|Sales|Sales Manager|feng.lin@company.com|90000 ``` ## Summary * sed reads from **stdin** or listed files by default. * Enclose scripts in single quotes to avoid shell expansion. * Use addresses (e.g., `2p`) to target specific lines. * The `-n` option disables automatic printing for precise control. * Place input files after the script. In upcoming lessons, we'll cover additional sed commands: * `d` **delete** lines * `s` **substitute** text * `i` **insert** text ## References * GNU sed Manual: [https://www.gnu.org/software/sed/manual/](https://www.gnu.org/software/sed/manual/) * Bash Reference Manual: [https://www.gnu.org/software/bash/manual/](https://www.gnu.org/software/bash/manual/)