test null behavior in shells

gistfile1.txt

#!/bin/bash

# Test script to understand null byte behavior across different shell constructs
# Run this with different shells: bash, zsh, dash, etc.

echo "=== Shell: $0 ==="
echo "Shell version info:"
if command -v bash >/dev/null 2>&1; then
    bash --version | head -1
fi
echo

# Helper function to show output with visible null bytes
show_output() {
    local desc="$1"
    shift
    echo "--- $desc ---"
    echo "Command: $*"
    echo -n "Output (od -c): "
    "$@" | od -c | head -1
    echo -n "Byte count: "
    "$@" | wc -c
    echo
}

echo "=== printf tests ==="
show_output "printf with \\x00" printf "before\\x00after"
show_output "printf with \\000" printf "before\\000after"  
show_output "printf with literal null" printf "before\x00after"

echo "=== echo tests ==="
show_output "echo with \\x00" echo "before\\x00after"
show_output "echo -e with \\x00" echo -e "before\\x00after"
show_output "echo with \$'\\x00'" echo $'before\x00after'
show_output "echo with \$'\\\\x00'" echo $'before\\x00after'

echo "=== variable expansion tests ==="
show_output "variable with literal null" sh -c 'a="before\x00after"; echo "$a"'
show_output "variable with \$'\\x00'" sh -c 'a=$'"'"'before\x00after'"'"'; echo "$a"'
show_output "variable with \$'\\\\x00'" sh -c 'a=$'"'"'before\\x00after'"'"'; echo "$a"'

echo "=== command substitution tests ==="
show_output "command subst with printf" sh -c 'echo "$(printf "before\\x00after")"'
show_output "command subst with echo \$''" sh -c 'echo "$(echo $'"'"'before\x00after'"'"')"'

echo "=== assignment and quoting ==="
show_output "assignment then printf %s" sh -c 'a=$'"'"'before\x00after'"'"'; printf "%s" "$a"'
show_output "assignment then echo" sh -c 'a=$'"'"'before\x00after'"'"'; echo "$a"'

echo "=== test with other escape sequences ==="
show_output "printf with \\n and \\x00" printf "line1\\nline2\\x00line3\\nline4"
show_output "printf with \\t and \\x00" printf "col1\\tcol2\\x00col3\\tcol4"

echo "=== edge cases ==="
show_output "printf empty \\x00" printf "\\x00"
show_output "printf only \\x00" printf "\\x00after"
show_output "printf \\x00 at end" printf "before\\x00"
show_output "multiple \\x00" printf "a\\x00b\\x00c"

echo "Done!"