I/O Handling in Shell Script - BunksAllowed

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    I/O Handling in Shell Script

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    Input

    To take an input from the user, read function is used. In the following script, the value of name variable is taken from standard input device (keyboard) using the line read name

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    #!/bin/bash
    echo "Enter your name:"
    read name
    echo "Welcome $name"
    XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

    Output

    To print messages to the terminal, the commonly used commands are printf and echo. The command echo is generally used to print a string with very simple formatting, whereas printf provides the scope of printing highly formatted output in flexible way.

    Printing a String using echo

    First, we will discuss different ways of use of echo command.


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    #!/bin/bash
    echo This a program.
    echo 'This a program.
    Do you want to Test?'
    echo "This a program.
    'Let us Test the code'"
    XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

    If you have a string in one line, you can put the string just after an echo. You may or may not include it in a single or double quote.

    But if you have a string written in multiple lines, you must include it in a single or double quote.

    Embedding Variables

    In the following example, we will discuss how to embed variables.


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    #!/bin/bash
    echo Hi $LOGNAME, your home directory is $HOME .
    XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

    Including Escape Sequence

    Similar to C programming language, in shell script escape sequences can be used. In the following example, we have shown how to use escape sequences in a script.


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    #!/bin/bash
    echo "Hi $LOGNAME, \nyour home directory is \t$HOME."
    XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

    A Script to print files in the current directory and their types using echo


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    #!/bin/bash
    echo "File Name\tType"
    for i in *;
    do
    echo "$i\t\c"
    if [ -d $i ]; then
    echo "is a directory."
    elif [ -h $i ]; then
    echo "is a symbolic link."
    elif [ -f $i ]; then
    echo "is a file."
    else
    echo "is unknown."
    fi
    done
    XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

    A Script to print files in the current directory and their types using printf


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    #!/bin/bash
    printf "%-32s %s\n" "File Name" "File Type"
    for i in *;
    do
    printf "%-32s " "$i"
    if [ -d "$i" ]; then
    echo "is a directory."
    elif [ -h "$i" ]; then
    echo "is a symbolic link."
    elif [ -f "$i" ]; then
    echo "is a file."
    else
    echo "is unknown."
    fi;
    done
    XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

    Output Redirection

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    #!/bin/bash
    ls -l >> list_of_files
    XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

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    #!/bin/bash
    { uptime; date; who; } >> users_log
    XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX


    Redirecting to Terminal and Screen

    Command tee is used to redirect output to the screen as well as the file.

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    #!/bin/bash
    { uptime; date; who; } | tee users_log
    XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX


    Happy Exploring!

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