readonly
Mark shell variables as read-only
TLDR
Make variable readonly
$ readonly [VAR]="[value]"
Make existing variable readonly$ readonly [VAR]
List readonly variables$ readonly
Make function readonly$ readonly -f [function_name]
Make array readonly$ readonly -a [ARRAY]
SYNOPSIS
readonly [options] [name[=value]...]
DESCRIPTION
readonly is a shell builtin that marks variables or functions as read-only, preventing modification or unsetting. Useful for constants and protecting configuration values.
PARAMETERS
-p
Print readonly variables.-f
Make functions readonly.-a
Make arrays readonly.-A
Make associative arrays readonly.
EXAMPLES
$ # Create readonly variable
readonly PI=3.14159
# Attempting to change fails
PI=3 # bash: PI: readonly variable
# Make existing readonly
CONFIG_FILE="/etc/app.conf"
readonly CONFIG_FILE
# Readonly function
myfunc() { echo "Hello"; }
readonly -f myfunc
# List all readonly
readonly -p
# Readonly array
readonly -a COLORS=("red" "green" "blue")
readonly PI=3.14159
# Attempting to change fails
PI=3 # bash: PI: readonly variable
# Make existing readonly
CONFIG_FILE="/etc/app.conf"
readonly CONFIG_FILE
# Readonly function
myfunc() { echo "Hello"; }
readonly -f myfunc
# List all readonly
readonly -p
# Readonly array
readonly -a COLORS=("red" "green" "blue")
IN SCRIPTS
$ #!/bin/bash
readonly SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
readonly CONFIG="${SCRIPT_DIR}/config.ini"
readonly VERSION="1.0.0"
readonly SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
readonly CONFIG="${SCRIPT_DIR}/config.ini"
readonly VERSION="1.0.0"
CAVEATS
Cannot unset readonly variables (until shell exits). Subshells don't inherit readonly status. Bash specific.
HISTORY
readonly is a POSIX shell builtin, with extended options in bash and other modern shells.
