brace

Shell syntax for grouping and expansion

TLDR

Command grouping (current shell)

$ { [command1]; [command2]; }

Brace expansion

$ echo {a,b,c}

Sequence expansion

$ echo {1..10}

Parameter expansion

$ echo ${var}

Create multiple files

$ touch file{1,2,3}.txt

SYNOPSIS

{ commands; }{a,b,c}{start..end}${parameter}

{ } (braces/curly brackets) serve multiple purposes in shell:Command grouping: { cmd1; cmd2; } groups commands to run in the current shell (unlike (...) which uses a subshell). Requires spaces after { and ; before }.Brace expansion: {a,b,c} expands to a b c. Useful for generating lists:- file{1,2,3} → file1 file2 file3- {a..z} → alphabet- {1..10} → numbers 1-10- {01..10} → zero-padded: 01 02 ... 10Parameter expansion: ${var} accesses variables, required for:- Array access: ${array[0]}- Modifiers: ${var:-default}- Disambiguation: ${var}text

EXAMPLES

$ # Group with redirect
{ echo "line1"; echo "line2"; } > file.txt

# Brace expansion for backups
cp config.{txt,bak}

# Generate sequences
mkdir dir{01..12}
echo {A..Z}

# Nested expansion
echo {a,b}{1,2} # a1 a2 b1 b2

CAVEATS

Command grouping requires space after { and semicolon before }: { cmd; } not {cmd}.Brace expansion is not glob expansion - it happens before other expansions and doesn't check if files exist.{} in find commands is the replacement string, not brace expansion.