Modest

${}变量替换

一般情况下，$var与${var}是没有区别的，但是用${ }会比较精确的界定变量名称的范围。

$ A=B
$ echo ${A}B
BB

command substitution

将命令输出的结果写入变量:

output=$(ls -l)
echo $output

函数定义

func_name () {
    command
}

split string

A="$(cut -d'_' -f2 <<<'one_two_three_four_five')"

或者

A="$(echo 'one_two_three_four_five' | cut -d'_' -f2)"

read line by line from file

while IFS='' read -r line; do
    echo "Text read from file: $line"
done < "$file"

or

while IFS='' read -r line || [[ -n "$line" ]]; do
    echo "Text read from file: $line"
done < "$1"

Explanation:

IFS='' (or IFS=) prevents leading/trailing whitespace from being trimmed.

-r prevents backslash escapes from being interpreted.

|| [[ -n $line ]] prevents the last line from being ignored if it doesn’t end with a \n (since read returns a non-zero exit code when it encounters EOF).