Bash read

External

• https://www.computerhope.com/unix/bash/read.htm
• https://www.baeldung.com/linux/read-command

Internal

• bash

Overview

read [-p prompt] name name2 ...

Read a line from the stdin or from the file descriptor specified with -u, and assign the first word to the variable associated with the first name, the second to the variable associated with the second name, and so on, with the leftover words and their intervening separators assigned to the variable associated with the last name. If there are fewer words than variable names, the variables associated with the remaining names are assigned empty values. If no names are supplied, the line read is assigned to the variable REPLY.

The words are split using the IFS characters. The backslash character (\) may be used to remove any special meaning for the next character read and for line continuation.

The return code is zero, unless end-of-file is encountered, read times out, or an invalid file descriptor is supplied as the argument to -u. On Ctrl-C, read returns 1.

If -p prompt option is used, read displays the specified prompt on standard error, without a trailing new-line, before attempting to read any input. The prompt is displayed only if input is coming from a terminal.

Exit Status

The exit status is 0 unless EOF is encountered, the timeout is exceeded, an error occurs assigning a value to name, or the file descriptor provided to -u is invalid.

If EOF is encountered, the exit status is 1.

If a timeout is exceeded, the exit status is greater than 128.

Options

-r

Use "raw input". Specifically, this option causes read to interpret backslashes literally, rather than interpreting them as escape characters.

-d

-d delim

Set the delimiter character to delim. This character signals the end of the line. If -d is not used, the default line delimiter is a newline.

-u

Read from the specified file descriptor instead of stdin. The file descriptor should be a small integer.

To open a file on a specified file descriptor, see:

bash Input/Output | Opening File Descriptors for Reading and Writing

-a

See Array Assignment below.

-s

See Silent Mode.

Timeout

-t timeout

causes read to timeout and return failure if a complete line of input is not read within timeout seconds. This option only works if read is reading input from stdin or a pipe.

Fixed Number of Characters

-n nchars

If -n option is used read returns after reading nchars characters rather than waiting for a complete line of input.

Array Assignment

-a aname

If -a option is used, the words are assigned to sequential indices of the array variable aname, starting at 0. aname is unset before any new values are assigned. Other name arguments are ignored.

See more:

bash Arrays

Silent Mode

-s

If input is coming from a terminal, characters are not echoed.

Examples

Confirmation to Proceed

function shall-we-proceed() {

    echo ""
    echo "This operation is dangerous, shall we proceed?"
    echo ""

    local answer

    read -r -p "y/n: " -n 1 answer || answer="n"

    echo ""

    [[ ${answer} = "y" ]] && return 0 || return 1
}

#
# usage
#

if ! shall-we-proceed; then
   echo "not proceeding ..."
   exit 0
fi

Read a Password with Confirmation

#
# If --ask-for-confirmation is among arguments, the password will be requested twice, for verification.
# Once a match is confirmed, the value will be returned to stdout.
function read-password() {

  local ask_for_confirmation=false
  while [[ -n $1 ]]; do
    if [[ $1 = "--ask-for-confirmation" ]]; then
      ask_for_confirmation=true
    fi
    shift
  done
  local password
  read -r -s -p "database root password: " password
  echo "" 1>&2
  if ${ask_for_confirmation}; then
    local password2
    read -r -s -p "repeat database root password: " password2
    echo "" 1>&2
    [[ ${password} != "${password2}" ]] && { echo "passwords do not match" 1>&2; exit 1; }
  fi
  echo ${password}
}

Reading Lines from File

Iterating over Lines from a File