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#!/bin/bash
# int-or-string.sh
a=2334 # Integer.
let "a += 1"
echo "a = $a " # a = 2335
echo # Integer, still.
b=${a/23/BB} # Substitute "BB" for "23".
# This transforms $b into a string.
echo "b = $b" # b = BB35
declare -i b # Declaring it an integer doesn't help.
echo "b = $b" # b = BB35
let "b += 1" # BB35 + 1
echo "b = $b" # b = 1
echo # Bash sets the "integer value" of a string to 0.
c=BB34
echo "c = $c" # c = BB34
d=${c/BB/23} # Substitute "23" for "BB".
# This makes $d an integer.
echo "d = $d" # d = 2334
let "d += 1" # 2334 + 1
echo "d = $d" # d = 2335
echo
# What about null variables?
e='' # ... Or e="" ... Or e=
echo "e = $e" # e =
let "e += 1" # Arithmetic operations allowed on a null variable?
echo "e = $e" # e = 1
echo # Null variable transformed into an integer.
# What about undeclared variables?
echo "f = $f" # f =
let "f += 1" # Arithmetic operations allowed?
echo "f = $f" # f = 1
echo # Undeclared variable transformed into an integer.
#
# However ...
let "f /= $undecl_var" # Divide by zero?
# let: f /= : syntax error: operand expected (error token is " ")
# Syntax error! Variable $undecl_var is not set to zero here!
#
# But still ...
let "f /= 0"
# let: f /= 0: division by 0 (error token is "0")
# Expected behavior.
# Bash (usually) sets the "integer value" of null to zero
#+ when performing an arithmetic operation.
# But, don't try this at home, folks!
# It's undocumented and probably non-portable behavior.
# Conclusion: Variables in Bash are untyped,
#+ with all attendant consequences.
exit $?
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