Theread Command#

The read command is used to read a single line of data from standard input. This command can be used to read input from the keyboard, and when used with redirection and default options, it can read a line of data from a file. In this case, read will consider the newline character as the line ending, but this can be changed using the -d option.

Syntax#

read [-ers] [-a array] [-d delim] [-i text] [-n nchars] [-N nchars] [-p prompt] [-t timeout] [-u fd] [name ...] [name2 ...]

Parameters#

• -a array: Store words in an indexed array named array, with array elements numbered starting at 0.
• -d delim: Set the delimiter to delim, which represents the line ending character. If not used, the default line delimiter is the newline character.
• -e: Get a line of input from the shell, allowing the user to manually input characters until the line delimiter is reached.
• -i text: When used with -e and only without -s, the text is inserted as the initial text of the input line, allowing the user to edit the text on the input line.
• -n nchars: Stop reading after reading nchars characters if the line delimiter has not been reached.
• -N nchars: Ignore the line delimiter and stop reading only after reading nchars characters, reaching EOF, or a read timeout.
• -p prompt: Print the prompt string without a newline before starting to read.
• -r: Use raw input, specifically, this option makes read interpret backslashes literally, rather than as escape characters.
• -s: When read gets input from the terminal, do not display the keystrokes.
• -t timeout: If the complete input line is not read within timeout seconds, it times out and returns failure. If the timeout value is zero, read will not read any data, but if input is available for reading, it returns success. If no timeout is specified, the value of the shell variable TMOUT (if it exists) is used. The timeout value can be a decimal, for example, 3.5.
• -u fd: Read from file descriptor fd instead of from standard input, where the file descriptor should be a small integer.

Examples#

Reading input from the terminal, continuously looping until pressing Ctrl + D to reach EOF. Since the variable name text is specified, the entire line of text is stored in the text variable, and the input content is output after pressing Enter for each line.

while read text
    do echo "$text"
done

Reading input from the terminal, specifying a timeout for the input.

if read -t 3 -p "Text: " text
then
    echo "Text: $text"
else
    echo -e "\nTimeout"
fi

Reading the contents of a file line by line.

cat test.txt | while read line
do
   echo "$line"
done

Daily Question#

References#