bash(1)

Expansion

Generator

# generate sequence from n to m
{n..m}
# generate sequence from n to m step by s
{n..m..s}

# expand cartesian product
{a,b}{c,d}

Parameter

# default param
# if $foo set, then bar=$foo else bar=some_val
bar=${foo:-some_val}

I/O redirection

Note: The trick with bash I/O redirection is to interpret from left-to-right.

# stdout & stderr to file
command >file 2>&1
# equivalent
command &>file

# stderr to stdout & stdout to file
command 2>&1 >file

Explanation

j>&i

Duplicate fd i to fd j, making j a copy of i. See dup2(2).

Example:

command 2>&1 >file

1. duplicate fd 1 to fd 2, effectively redirecting stderr to stdout
2. redirect stdout to file