- Magic #! line, the bare option - says that there are no more shell options; this is a security feature to prevent certain kinds of spoofing attacks.
#! /bin/sh - -
two dashes -- should be used to signify the end of options.
-
To force POSIX behavior, invoke bash with the --posix option or run set -o posix in the shell.
－ A here string can be considered as a stripped-down form of a here document.
It consists of nothing more than COMMAND <<< ["]$WORD["],
where $WORD is expanded and fed to the stdin of COMMAND.
-
The trap command allows you to execute a command when a signal is received by your script. It works like this:
trap "commands" signals -
set: Set or unset values of shell options and positional parameters. Change the value of shell attributes and positional parameters, or display the names and values of shell variables.
set --: If no arguments follow this option, then the positional parameters are unset. Otherwise, the positional parameters are set to the arguments, even if some of them begin with a ‘-’. -
Leading Zeros and Base Selection Constants with a leading 0 are interpreted as octal numbers. A leading ‘0x’ or ‘0X’ denotes hexadecimal. Otherwise, numbers take the form [base#]n, where the optional base is a decimal number between 2 and 64 representing the arithmetic base, and n is a number in that base. If base# is omitted, then base 10 is used. When specifying n, the digits greater than 9 are represented by the lowercase letters, the uppercase letters, ‘@’, and ‘_’, in that order. If base is less than or equal to 36, lowercase and uppercase letters may be used interchangeably to represent numbers between 10 and 35.