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In Bash, use the read builtin to obtain a line typed by a user:
#!/usr/bin/env bash
IFS= read -r -p "Enter your name: " name
printf 'Hello, %s!n' "$name"read normally consumes standard input, which may be the keyboard, a pipe, or a redirected file. The recommended general-purpose form, IFS= read -r, preserves leading and trailing whitespace and treats backslashes literally.
The basic read command
Create a file named hello.sh:
#!/usr/bin/env bash
read -r -p "Enter your name: " name
printf 'Hello, %s!n' "$name"Make it executable and run it:
chmod +x hello.sh
./hello.shA typical interaction is:
Enter your name: Ada Lovelace
Hello, Ada Lovelace!The variable is assigned without a dollar sign: name, not $name. The dollar sign is used when expanding the value later. Always quote an expansion such as "$name" when it represents one value.
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For Bash’s complete read syntax and option behavior, see the GNU Bash Builtins reference.
Keyboard input is usually standard input
Although tutorials often call this “keyboard input,” read does not inherently know whether data came from a keyboard. Without redirection, it reads file descriptor 0, called standard input (stdin). Standard input can come from:
- An interactive terminal and its keyboard.
- A pipe from another command.
- A file supplied with input redirection.
read -r value # normally reads stdin
printf '%sn' value | read -r value
read -r value < input.txtThe second example also illustrates a Bash pitfall: a loop or command in a pipeline can run in a subshell, so assignments may not remain available afterward. Read on for a safer pattern.
The safest default for a complete line
IFS= read -r valueThis form is not ceremonial syntax:
IFS=preventsreadfrom removing or splitting leading and trailing whitespace when assigning a complete line.-rprevents backslashes from being interpreted as escape characters or as part of a backslash-newline continuation.
Use it for names, sentences, paths, copied text, regular expressions, and other values whose exact characters matter:
IFS= read -r -p "Enter a directory path: " directory
printf 'You entered: <%s>n' "$directory"Without -r, an input such as C:Tempfiles may not be stored exactly as typed. Without IFS=, surrounding spaces can be removed or interpreted as field separators.
Displaying a prompt
The -p option displays a prompt without a trailing newline:
IFS= read -r -p "Project name: " projectBash displays this prompt when input is coming from a terminal. If standard input is redirected or piped, the prompt may not appear. When you want explicit prompt control, write the prompt to standard error and read standard input separately:
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IFS= read -r projectWriting prompts to standard error keeps standard output available for data that another command may capture or pipe.
Checking whether input succeeded
read returns a success status when it obtains the requested input. It returns nonzero for conditions such as end-of-file, a timeout, an invalid file descriptor, or certain assignment errors.
if IFS= read -r -p "Enter your name: " name; then
printf 'Hello, %s!n' "$name"
else
printf 'No input was received.n' >&2
exit 1
fiAn empty line is different from failed input. Pressing Enter can be a successful read whose value contains zero characters:
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if [[ -z $name ]]; then
printf 'The name cannot be empty.n' >&2
fiIn other words:
- Empty input: a line was read successfully, but it contained no characters.
- EOF: no more input is available.
- Timeout: the required input was not completed in time.
- Invalid input: a line was read, but it does not satisfy your application’s rules.
For files whose last line may not end with a newline, use:
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printf 'Line: %sn' "$line"
done < input.txtReading multiple values
Multiple variable names make read split the line into fields using IFS:
read -r -p "Enter first and last name: " first last
printf 'First: %snLast: %sn' "$first" "$last"This is suitable only when whitespace-separated fields are intended. If there are more fields than variables, the remaining text is assigned to the last variable. If there are fewer fields, remaining variables become empty.
read -r -p "Enter three numbers: " n1 n2 n3For an arbitrary whitespace-separated list, use an indexed array:
read -r -a items
printf 'Item count: %dn' "${#items[@]}"
for item in "${items[@]}"; do
printf '<%s>n' "$item"
doneThe -a option assigns fields beginning at array index zero and clears the array’s previous elements. Do not use Bash field splitting as a CSV parser; quoted commas, embedded newlines, and escaping require a format-aware tool.
Validating user input
read captures text but does not decide whether that text is acceptable. Validate before using it.
Required values
while :; do
if ! IFS= read -r -p "Username: " username; then
printf 'nInput ended before a username was entered.n' >&2
exit 1
fi
if [[ -n $username ]]; then
break
fi
printf 'Please enter a username.n' >&2
doneWhole numbers
while :; do
IFS= read -r -p "Enter a whole number: " number
if [[ $number =~ ^[0-9]+$ ]]; then
break
fi
printf 'Please enter digits only.n' >&2
doneFor signed integers, use a pattern such as ^-?[0-9]+$. Do not perform arithmetic evaluation on unvalidated input:
# Do not do this before validation:
(( result = user_input + 1 ))Yes/no answers
while :; do
IFS= read -r -p "Continue? [y/n] " answer
case ${answer,,} in
y|yes) break ;;
n|no) exit 0 ;;
*) printf 'Please answer y or n.n' >&2 ;;
esac
done${answer,,} is Bash syntax for lowercasing a value. It is not portable to every shell, so keep the Bash requirement explicit.
Choice menus
Bash’s select builtin creates a numbered menu:
select choice in "Start" "Stop" "Quit"; do
case $REPLY in
1) printf 'Startingn'; break ;;
2) printf 'Stoppingn'; break ;;
3) exit 0 ;;
*) printf 'Invalid selection.n' >&2 ;;
esac
doneselect is Bash-specific. The numeric response is stored in REPLY; the selected text is stored in choice.
Paths and destructive commands
Quote values and, where supported, use -- to mark the end of options:
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command -- "$value"For example:
rm -rf -- "$directory"Quoting prevents word splitting and pathname expansion, but it does not make a destructive operation safe. Validate the path, reject unexpected locations, and request explicit confirmation before deleting anything.
Password and secret input
Use -s to suppress character echo when reading a password from a terminal:
if IFS= read -r -s -p "Password: " password; then
printf 'n'
else
printf 'nUnable to read the password.n' >&2
exit 1
fi-s hides terminal echo; it does not encrypt the value, erase it from memory, prevent logging, or secure it against every form of exposure. Never print the captured password:
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printf 'Password: %sn' "$password"Avoid set -x while handling secrets because shell tracing can reveal commands and expanded values. Do not place passwords on command lines, where they may be exposed through shell history or process inspection. Environment variables and temporary files also have security trade-offs.
Timeouts and character input
Time-limited input
if IFS= read -r -t 10 -p "Enter a value within 10 seconds: " value; then
printf 'Received: %sn' "$value"
else
printf 'Input ended, timed out, or failed.n' >&2
fi-t causes read to fail if the requested input is not completed within the specified time. Bash accepts fractional values such as 2.5. A failed read is not proof of a timeout: EOF and other failures are also possible. The option does not affect ordinary regular-file input.
Reading one or more characters
For a simple menu or confirmation:
if IFS= read -r -n 1 -p "Continue? [y/N] " answer; then
printf 'n'
fi-n reads up to the requested number of characters, but a delimiter or EOF can finish the read sooner. Bash’s -N option instead waits for exactly the requested number of characters, unless EOF or an error occurs:
read -r -N 4 codeUnlike -n, -N does not treat delimiter characters as an early stopping point and does not split the result using IFS.
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Custom delimiters and NUL-separated input
Use -d to stop at a chosen delimiter:
IFS= read -r -d ':' valueAn empty delimiter argument tells Bash to stop at a NUL byte:
IFS= read -r -d '' valueNUL-delimited records are useful when processing filenames from commands designed to handle arbitrary filenames. Ordinary interactive text is normally newline-delimited, so do not use this form unless the producer and consumer agree on the format.
Reading from files, pipes, and file descriptors
Use -u to read from a particular open file descriptor instead of standard input:
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exec 3< input.txt
while IFS= read -r -u 3 line; do
printf '%sn' "$line"
done
exec 3<&-This is useful when a script reads a data file while keeping standard input available for a user:
exec 3< users.txt
IFS= read -r -p "Enter a value: " value
IFS= read -r -u 3 first_user
exec 3<&-Close descriptors when they are no longer needed. For simple file processing, redirection on the loop is often clearer:
while IFS= read -r line; do
printf '%sn' "$line"
done < input.txtReading from the keyboard when standard input is redirected
If a script’s standard input is occupied by a pipe or file, an ordinary read will consume that data rather than waiting for the keyboard. On a normal terminal, read directly from /dev/tty:
IFS= read -r -p "Confirm: " answer </dev/ttyA more defensive approach first checks whether standard input is a terminal and falls back to file descriptor 3:
if [[ -t 0 ]]; then
input_fd=0
else
exec 3</dev/tty || {
printf 'No interactive terminal is available.n' >&2
exit 1
}
input_fd=3
fi
IFS= read -r -u "$input_fd" -p "Value: " value
if (( input_fd == 3 )); then
exec 3<&-
fi/dev/tty is normally available in a terminal session, but it may not exist or be usable in cron, services, containers without a TTY, or other noninteractive environments. A script should fail clearly or provide a noninteractive alternative rather than assuming a terminal exists.
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Pipeline loops and subshells
This common pattern may not preserve last after the loop:
printf '%sn' one two |
while IFS= read -r item; do
last=$item
done
printf '%sn' "$last"In Bash execution contexts where the last pipeline component runs in a subshell, the assignment disappears when that subshell exits. Use process substitution when the loop must update variables in the current shell:
while IFS= read -r item; do
last=$item
done < <(printf '%sn' one two)
printf '%sn' "$last"Alternatively, redirect a loop from a file or use an array when that better matches the data model.
Readline editing and completion
For interactive tools, -e enables Bash Readline editing when standard input is a terminal:
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read -r -e -p "File: " fileYou can pre-fill the editing buffer with -i:
read -r -e -i "default.txt" -p "File: " file-E selects Bash’s default completion behavior, including programmable completion. These options are terminal-oriented and should not be assumed to work meaningfully for piped or automated input.
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A reusable required-input function
For a larger Bash script, a function can centralize prompting and validation:
prompt_required() {
local prompt=$1
local __resultvar=$2
local answer
while :; do
IFS= read -r -p "$prompt" answer || return 1
if [[ -n $answer ]]; then
printf -v "$__resultvar" '%s' "$answer"
return 0
fi
printf 'A value is required.n' >&2
done
}
if prompt_required 'Name: ' name; then
printf 'Hello, %sn' "$name"
filocal limits temporary variables to the function. printf -v assigns the result without reparsing it as shell code. This function adds Bash concepts and may be unnecessary for a tiny script, but it gives a larger script consistent behavior for required prompts.
Common mistakes and fixes
| Problem | Better approach |
|---|---|
| Backslashes disappear | Use IFS= read -r value. |
| Leading or trailing spaces disappear | Use an empty IFS assignment for that read. |
| Input is split unexpectedly | Read the complete line into one variable instead of using multiple variable names. |
| A prompt is missing in a pipeline | Prompts are terminal-oriented; use printf ... >&2 and, when appropriate, read from /dev/tty. |
| The script appears to skip input | Check whether a previous command consumed the line and whether [[ -t 0 ]] reports a terminal. |
| The final file line is skipped | Use while IFS= read -r line || [[ -n $line ]]. |
| User input breaks a command | Quote expansions and use -- where supported. |
| User input executes as a command | Never pass raw input to eval or construct a shell command for sh -c. |
Never execute raw input
Input should be treated as data, not shell source:
# Unsafe:
read -r command
eval "$command"
# Also dangerous:
sh -c "$user_input"If a user must choose an operation, map an allowed value to a fixed command:
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*) printf 'Invalid choice.n' >&2; exit 2 ;;
esacQuoting protects against many word-splitting and globbing bugs, but it does not make arbitrary shell evaluation safe.
Interactive prompts versus automation
Interactive input is convenient for humans but unsuitable for many cron jobs, CI pipelines, configuration-management runs, SSH commands without a terminal, and containers launched without a TTY.
For a script that supports both command-line use and interactive fallback:
name=${1-}
if [[ -z $name ]]; then
IFS= read -r -p "Name: " name
fi
printf 'Hello, %sn' "$name"For proper command-line options, use Bash’s getopts rather than prompting for every setting. Arguments, environment variables, configuration files, and standard input are usually better interfaces for automation. Prompt only when an interactive terminal is intentionally part of the design.
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- Use
IFS= read -r linefor one complete line of text. - Use multiple variables only when whitespace-separated fields are intentional.
- Use
-afor a whitespace-separated list. - Use
-sfor basic hidden terminal entry, while remembering that it is not encryption. - Use
-twhen an interactive operation needs a deadline. - Use
-uor/dev/ttywhen standard input is being used for something else. - Validate before arithmetic, filesystem operations, or selecting an action.
- Prefer noninteractive arguments or
getoptswhen another program will invoke the script.
Complete example
The following script combines successful reads, required-value validation, and silent secret entry:
#!/usr/bin/env bash
set -u
while :; do
if ! IFS= read -r -p "Enter your name: " name; then
printf 'nInput ended before a name was entered.n' >&2
exit 1
fi
if [[ -n $name ]]; then
break
fi
printf 'The name cannot be empty.n' >&2
done
if IFS= read -r -s -p "Enter a secret: " secret; then
printf 'n'
else
printf 'nUnable to read the secret.n' >&2
exit 1
fi
printf 'Hello, %s!n' "$name"
# Use "$secret" only where necessary; never print it.The first loop distinguishes a successful empty line from EOF and keeps prompting until a nonempty name is received. The second read suppresses terminal echo and prints a separate newline afterward because the prompt itself does not add one. The secret remains available to later code but is never displayed.
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