bash-hackers-wiki/docs/commands/builtin/read.md

# The read builtin command

*read something about read here!*

## Synopsis

    read [-ers] [-u <FD>] [-t <TIMEOUT>] [-p <PROMPT>] [-a <ARRAY>] [-n <NCHARS>] [-N <NCHARS>] [-d <DELIM>] [-i <TEXT>] [<NAME...>]

## Description

The `read` builtin reads **one line** of data (text, user input, ...)
from standard input or a supplied filedescriptor number into one or more
variables named by `<NAME...>`.

Since Bash 4.3-alpha, `read` skips any `NUL` (ASCII code 0) characters
in input.

If `<NAME...>` is given, the line is word-split using
[IFS](../../syntax/shellvars.md#IFS) variable, and every word is assigned to one
`<NAME>`. The remaining words are all assigned to the last `<NAME>` if
more words than variable names are present.

!!! INFO
    If no `<NAME>` is given, the whole line
    read (without performing word-splitting!) is assigned to the shell
    variable [REPLY](../../syntax/shellvars.md#REPLY). Then, `REPLY` really contains
    the line as it was read, without stripping pre- and postfix spaces and
    other things!

        while read -r; do
          printf '"%s"\n' "$REPLY"
        done <<<"  a line with prefix and postfix space  "

If a timeout is given, or if the shell variable
[TMOUT](../../syntax/shellvars.md#TMOUT) is set, it is counted from initially
waiting for input until the completion of input (i.e. until the complete
line is read). That means the timeout can occur during input, too.

### Options

|Option|Description|
|------|-----------|
|`-a <ARRAY>`|read the data word-wise into the specified array `<ARRAY>` instead of normal variables|
|`-d <DELIM>`|recognize `<DELIM>` as data-end, rather than `<newline>`|
|`-e`|on interactive shells: use Bash's readline interface to read the data. Since version 5.1-alpha, this can also be used on specified file descriptors using `-u`|
|`-i <STRING>`|preloads the input buffer with text from `<STRING>`, only works when Readline (`-e`) is used|
|`-n <NCHARS>`|reads `<NCHARS>` characters of input, then quits|
|`-N <NCHARS>`|reads `<NCHARS>` characters of input, *ignoring any delimiter*, then quits|
|`-p <PROMPT>`|the prompt string `<PROMPT>` is output (without a trailing automatic newline) before the read is performed|
|`-r`|raw input - **disables** interpretion of **backslash escapes** and **line-continuation** in the read data|
|`-s`|secure input - don't echo input if on a terminal (passwords!)|
|`-t <TIMEOUT>`|wait for data `<TIMEOUT>` seconds, then quit (exit code 1). Fractional seconds ("5.33") are allowed since Bash 4. A value of 0 immediately returns and indicates if data is waiting in the exit code. Timeout is indicated by an exit code greater than 128. If timeout arrives before data is read completely (before end-of-line), the partial data is saved.|
|`-u <FD>`|use the filedescriptor number `<FD>` rather than `stdin` (0)|

When both, `-a <ARRAY>` and a variable name `<NAME>` is given, then the
array is set, but not the variable.

Of course it's valid to set individual array elements without using
`-a`:

    read MYARRAY[5]

!!! WARNING
    Reading into array elements using the syntax above **may cause [pathname
    expansion](../../syntax/expansion/globs.md) to occur**.

    Example: You are in a directory with a file named `x1`, and you want to
    read into an array `x`, index `1` with

        read x[1]

    then pathname expansion will expand to the filename `x1` and break your
    processing!

    Even worse, if `nullglob` is set, your array/index will disappear.

    To avoid this, either **disable pathname expansion** or **quote** the
    array name and index:

        read 'x[1]'

### Return status

|Status|Reason|
|------|------|
|0|no error|
|0|error when assigning to a read-only variable [^1]|
|2|invalid option|
|>128|timeout (see `-t`)|
|!=0|invalid filedescriptor supplied to `-u`|
|!=0|end-of-file reached|

### read without -r

Essentially all you need to know about `-r` is to **ALWAYS** use it. The
exact behavior you get without `-r` is completely useless even for weird
purposes. It basically allows the escaping of input which matches
something in IFS, and also escapes line continuations. It's explained
pretty well in the [POSIX
read](http://pubs.opengroup.org/onlinepubs/9699919799/utilities/read.html#tag_20_109)
spec.

    2012-05-23 13:48:31 geirha  it should only remove the backslashes, not change \n and \t and such into newlines and tabs
    2012-05-23 13:49:00 ormaaj  so that's what read without -r does?
    2012-05-23 13:49:16 geirha  no, -r doesn't remove the backslashes
    2012-05-23 13:49:34 ormaaj  I thought read <<<'str' was equivalent to read -r <<<$'str'
    2012-05-23 13:49:38 geirha  # read x y <<< 'foo\ bar baz'; echo "<$x><$y>"
    2012-05-23 13:49:40 shbot   geirha: <foo bar><baz>
    2012-05-23 13:50:32 geirha  no, read without -r is mostly pointless. Damn bourne
    2012-05-23 13:51:08 ormaaj  So it's mostly (entirely) used to escape spaces
    2012-05-23 13:51:24 ormaaj  and insert newlines
    2012-05-23 13:51:47 geirha  ormaaj: you mostly get the same effect as using \ at the prompt
    2012-05-23 13:52:04 geirha  echo \"  outputs a " ,  read x <<< '\"'  reads a "
    2012-05-23 13:52:32 ormaaj  oh weird
    2012-05-23 13:52:46  *  ormaaj struggles to think of a point to that...
    2012-05-23 13:53:01 geirha  ormaaj: ask Bourne :P
    2012-05-23 13:53:20 geirha  (not Jason)
    2012-05-23 13:53:56 ormaaj  hm thanks anyway :)

## Examples

### Rudimentary cat replacement

A rudimentary replacement for the `cat` command: read lines of input
from a file and print them on the terminal.

    opossum() {
      while read -r; do
        printf "%s\n" "$REPLY"
      done <"$1"
    }

<u>**Note:**</u> Here, `read -r` and the default `REPLY` is used,
because we want to have the real literal line, without any mangeling.
`printf` is used, because (depending on settings), `echo` may interpret
some baskslash-escapes or switches (like `-n`).

### Press any key...

Remember the MSDOS `pause` command? Here's something similar:

    pause() {
      local dummy
      read -s -r -p "Press any key to continue..." -n 1 dummy
    }

Notes:

-   `-s` to suppress terminal echo (printing)
-   `-r` to not interpret special characters (like waiting for a second
    character if somebody presses the backslash)

### Reading Columns

#### Simple Split

Read can be used to split a string:

    var="one two three"
    read -r col1 col2 col3 <<< "$var"
    printf "col1: %s col2: %s col3 %s\n" "$col1" "$col2" "$col3"

Take care that you cannot use a pipe:

    echo "$var" | read col1 col2 col3 # does not work!
    printf "col1: %s col2: %s col3 %s\n" "$col1" "$col2" "$col3"

Why? because the commands of the pipe run in subshells that cannot
modify the parent shell. As a result, the variables `col1`, `col2` and
`col3` of the parent shell are not modified (see article:
[processtree](../../scripting/processtree.md)).

If the variable has more fields than there are variables, the last
variable get the remaining of the line:

    read col1 col2 col3 <<< "one two three four"
    printf "%s\n" "$col3" #prints three four

#### Changing The Separator

By default reads separates the line in fields using spaces or tabs. You
can modify this using the *special variable*
[IFS](../../syntax/shellvars.md#IFS), the Internal Field Separator.

    IFS=":" read -r col1 col2 <<< "hello:world"
    printf "col1: %s col2: %s\n" "$col1" "$col2"

Here we use the `var=value command` syntax to set the environment of
`read` temporarily. We could have set `IFS` normally, but then we would
have to take care to save its value and restore it afterward
(`OLD=$IFS IFS=":"; read ....;IFS=$OLD`).

The default `IFS` is special in that 2 fields can be separated by one or
more space or tab. When you set `IFS` to something besides whitespace
(space or tab), the fields are separated by **exactly** one character:

    IFS=":" read -r col1 col2 col3 <<< "hello::world"
    printf "col1: %s col2: %s col3 %s\n" "$col1" "$col2" "$col3"

See how the `::` in the middle infact defines an additional *empty
field*.

The fields are separated by exactly one character, but the character can
be different between each field:

    IFS=":|@" read -r col1 col2 col3 col4 <<< "hello:world|in@bash"
    printf "col1: %s col2: %s col3 %s col4 %s\n" "$col1" "$col2" "$col3" "$col4"

### Are you sure?

    asksure() {
    echo -n "Are you sure (Y/N)? "
    while read -r -n 1 -s answer; do
      if [[ $answer = [YyNn] ]]; then
        [[ $answer = [Yy] ]] && retval=0
        [[ $answer = [Nn] ]] && retval=1
        break
      fi
    done

    echo # just a final linefeed, optics...

    return $retval
    }

    ### using it
    if asksure; then
      echo "Okay, performing rm -rf / then, master...."
    else
      echo "Pfff..."
    fi

### Ask for a path with a default value

<u>**Note:**</u> The `-i` option was introduced with Bash 4

    read -e -p "Enter the path to the file: " -i "/usr/local/etc/" FILEPATH

The user will be prompted, he can just accept the default, or edit it.

### Multichar-IFS: Parsing a simple date/time string

Here, `IFS` contains both, a colon and a space. The fields of the
date/time string are recognized correctly.

    datetime="2008:07:04 00:34:45"
    IFS=": " read -r year month day hour minute second <<< "$datetime"

## Portability considerations

-   POSIX(r) only specified the `-r` option (raw read); `-r` is not only
    POSIX, you can find it in earlier Bourne source code
-   POSIX(r) doesn't support arrays
-   `REPLY` is not POSIX(r), you need to set `IFS` to the empty string
    to get the whole line for shells that don't know `REPLY`.
    `while IFS= read -r line; do
      ...
    done < text.txt
    `

## See also

-   Internal: [The printf builtin command](../../commands/builtin/printf.md)

[^1]: fixed in 4.2-rc1