Bash

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Bash Shell

1. Arguments

2. Some Scripts

2.1. Modify the brightness of Arch Linux

Put a number into /sys/class/backlight/intel_backlight/brightness represent the brightness. The max number of brightness is denoted in file /sys/class/backlight/intel_backlight/max_brightness.

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#!/bin/bash
flag=true
max_light=$(cat /sys/class/backlight/intel_backlight/max_brightness)

read -p "please input a number in range (0, $max_light):" num

while $flag
do
  # >name, means 1>name -- redirect stdout to the file name
  # &>name, is like 1>name 2>name -- redirect stdout and stderr to the file name (however, name is only opened once; if you actually wrote 1>name 2>name, it'd try to open name twice and perhaps malfunction.)
  # expr performs the arithmetic operations
  # if the input num is not a number then an error will produce
  # $? can capture the error, if expr is executed correctly, $? == 0, else it is the number represent the error type.

         expr $num + 0 &>/dev/null
         # $ false || echo "Oops, fail"
         # Oops, fail

          # $ true || echo "Will not be printed"
          # $

          # $ true && echo "Things went well"
          # Things went well

          # $ false && echo "Will not be printed"
          # $
          # for && the right command will be executed, only the left command is true
          # for || the left command will be executed, only the left command is false
          # thus when [xxx] is true flag=true will be executed and the last command will
          # not be executed.
          # when [xxx] is false, flag=false will never be executed and the last command
          # will be executed.
         [[ $? -eq 0 && $num -ge 0 && $num -le $max_light ]] && flag=false || read -p "please input a number in range (0, $max_light):" num
done
echo $num > /sys/class/backlight/intel_backlight/brightness

2.2. run tmux only open a terminal

Add this to the .bashrc.

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#  Note: the spaces after the [ and before the ] are necessary.
# tmux will be executed only if it is opened by st
if [ "$TERM" = "st-256color" ]; then
	tmux
fi