• #!/bin/bash
• ps | grep $$
• which bash
• ${PWD##*/} ＃当前目录名

note

• shell加载的file修改过需要 source path重新加载下

var

$var

转义 A backslash "\" is used to escape special character meaning

"" 保持原样. Encapsulating the variable name with "" will preserve any white space values

`` command命令 (known as back-ticks) or with $()

read var_name #get input

Passing Arguments to the Script

从1开始计算$n

./bin/my_shopping.sh apple 5 banana 8 "Fruit Basket" 15
echo $3 --> results with: banana

The variable $# holds the number of arguments passed to the script

Array

• my_array=()
• ${my_array[i]}
• ${#my_array[@]} #len

my_array=(apple banana "Fruit Basket" orange)
echo ${my_array[3]}                     # orange - note that curly brackets are needed
my_array[4]="carrot"                    # value assignment without a $ and curly brackets
echo ${#my_array[@]}                    # 5
echo ${my_array[${#my_array[@]}-1]}     # carrot

Basic Arithmetic Operators

$((expression))

• • • • / % **

String Operations

• ${#STRING} #len
• expr index "$STRING" "$SUBSTRING" #SUBSTRING 中任意char 第一个match string的index（从1开始）

• substring

  • STRING="this is a string" POS=1 LEN=3 echo ${STRING:$POS:$LEN} # his
  • echo ${STRING:2} # his is a string

• Simple data extraction example:

        DATARECORD="last=Clifford,first=Johnny Boy,state=CA"
        COMMA1=`expr index "$DATARECORD" ','`  # 14 position of first comma
        CHOP1FIELD=${DATARECORD:$COMMA1}       #
        COMMA2=`expr index "$CHOP1FIELD" ','`
        LENGTH=`expr $COMMA2 - 6 - 1`
        FIRSTNAME=${CHOP1FIELD:6:$LENGTH}      # Johnny Boy
        echo $FIRSTNAME

• replace string

        STRING="to be or not to be"
        echo ${STRING[@]/be/eat}        # to eat or not to be
        echo ${STRING[@]//be/eat}        # to eat or not to eat
        echo ${STRING[@]/#to be/eat now}    # eat now or not to be #replace beginning
        echo ${STRING[@]/%be/eat}        # to be or not to eat #replace end 
        echo ${STRING[@]/%be/be on $(date +%Y-%m-%d)}    # to be or not to be on 2012-06-14 #replace occurrence of substring with shell command output

Making Decision

• == != < >
• -z "$a"判空

if [ expression ]; then code if 'expression' is true elif [ expression2 ]; then code fi

case "$variable" in "$condition1" ) command... ;; "$condition2" ) command... ;; esac

mycase=1
case $mycase in
    1) echo "You selected bash";;
    2) exit
esac

Loop

• break
• continue

for arg in [list] do command(s)... done

while [ condition ] do command(s)... done

until [ condition ] do command(s)... done

NAMES=(Joe Jenny Sara Tony)
for N in ${NAMES[@]} ; do
      echo "My name is $N"
done

COUNT=4
while [ $COUNT -gt 0 ]; do
      echo "Value of count is: $COUNT"
      COUNT=$(($COUNT - 1))
done

function

function_name { command... }

function adder {
      echo "$(($1 + $2))"
}

多进程

• sleep 1 睡眠1秒
• sleep 1s 睡眠1秒
• sleep 1m 睡眠1分
• sleep 1h 睡眠1小时
• wait [n] 等待进程号为n的后台进程终止

...
{command...} & #后台进程执行
...
wait #wait前面后台进程执行完毕

参数处理

• $# 传递到脚本的参数个数
• $ 以一个单字符串显示所有向脚本传递的参数。 如"$"用「"」括起来的情况、以"$1 $2 … $n"的形式输出所有参数。
• $$ 脚本运行的当前进程ID号
• $! 后台运行的最后一个进程的ID号
• $@ 与$相同，但是使用时加引号，并在引号中*返回每个参数。 如"$@"用「"」括起来的情况、以"$1" "$2" … "$n" 的形式输出所有参数。
• $- 显示Shell使用的当前选项，与set命令功能相同。
• $? 显示最后命令的退出状态。0表示没有错误，其他任何值表明有错误。

env

• source makes the changes available right away in the session we are in.
• ~/.bash_profile bash profile for current user
• alias alias pd="pwd" ncommand allows you to create keyboard shortcuts,
• environment variables are variables that can be used across commands and programs and hold information about the environment.
  • $PATH $HOME
• export makes the variable to be available to all child sessions initiated from the session you are in
• PS1 export PS1=">> " PS1 is a variable that defines the makeup and style of the command prompt
• env returns a list of the environment variables for the current user