bash: syntax and commands

  • array
    • normal array: using integer as index
    •  associative array: using string as index (after BASH 4.0)
  • user
    • sudo <command> <arguments>: to work as root user
  • file
    • echo
    • printf
    • redirect cmd to file, redirect data can't to use for pipeline:
      • cmd > out.txt; #stdout to out.txt 
      • cmd 2> err.txt; #stderr to err.txt
      • cmd 2>err.txt 1>out.txt; 
      • cmd > all.txt 2>&1; cmd &> all.txt; #stdout and stderr to all.txt
    • tee: redirect and to pipeline
    • redirect file to cmd
      • cmd < file 
      • cmd<< #here document
      • cmd<<< #here string
    • file handler
    • cat: concatenate files and print to stdout
  • math
    • let
    • (())
    • []
    • expr
    • bc
  • for easily usage of terminal
    • alias
    • terminal
      • tput: to get some terminal infos, column number, line numbers, cursor position, color...
      • stty: change terminal settings
  • system resource
    • time
      • date
      • nptdate: get time from internet
      • time
      • sleep
    • process and Env
      • pgrep <command name>: to get command process
        • /proc/$PID/environ: process <PID>'s environment
  • ENV
    • export: export <env_var>: the env_var will get by any procedure launch by current shell 
  • arguments
    • ${parameter:expression}: if parameter exist and is not empty, using the value of expression
  • built-in
    •  length = ${#var}: get length of var
    • echo $SHELL: get current shell
    • echo $0: get current shell, some situations it is different with echo $SHELL
    • []: it is a command

 

  •  array 
    • #!/bin/bash

###basic array####
##def
array_var1=(test1 test2 test3 test4)

array_var2[0]="test1"
array_var2[1]="test2"
array_var2[2]="test3"
array_var2[3]="test4"
array_var2[4]="test5"
array_var2[5]="test6"

##print
echo ${array_var1[0]}
index=5
echo ${array_var2[$index]}

echo ${array_var1[*]}
echo ${array_var1[@]}
# > test1 test2 test3 test4

echo ${#array_var1[*]}
# > 4
echo ${!array_var1[*]}
# > 0 1 2 3


####accociative array####
##def
declare -A test_array
test_array=([type1]=orange [type2]=apple)
test_array[type3]=lemon
echo ${!test_array[*]}
echo ${test_array[*]}
# > type3 type1 type2
# > lemon orange apple　
  • echo
    • echo -e "<string with regexp>"
    • $ echo -e "1\t2\t3"
> 1    2    3
    • set color
    • \e[1,31m: to set color red
    • \e[0m: to reset color
    • for text: reset=0; black=30; red=31; green=32; yellow=33; blue=34; magenta=35; cyan=36; white=37
    • for background: reset=0; black=40; red=41; green=42; yellow=43; blue=44; magenta=45; cyan=46; white=47
    • $ echo -e "\e[1;31m test \e[0m"
> test　

       

    • $ echo -e "\e[1;41m test \e[0m"
> test

      　　　　

  • printf
    • %s, %c, %d, %f
    • -: left justifying
    • $ printf "%-5s %-5s %-5s\n" This is test
> This  is    test

 

  • tee
    • get data from stdin and redirect them to stdout and to a file 
    • cmd | tee FILE1 FILE2 | otherCmd
    • cmd | tee -  #send data twice to stdout
    • $ echo A1 > a1
$ echo A2 > a2
$ echo A3 > a3
$ cat a* | tee out.txt | cat -n
> 1 A1
> 2 A2
> 3 A3
$ more out.txt
> A1
> A2
> A3
$ echo add > add.txt
$ cat add.txt| tee -a out.txt|cat -n #append to file out.txt
> 1 add
$ more out.txt
> A1
> A2
> A3
> add
$ echo test | tee - #redirect to stdout twice, but not redirect to any file
> test
> test
  • <redirection> 
    • #!/bin/bash
# > : stdout to file
# >> : append stdout to file
# < : file to cmd

#redirect text in script to another file
# all txt between cat line and EOF line will write into log.txt
cat << EOF > log.txt
This is a general file. Don't edit it.
add more.
add more.
EOF
  • file handler 
    • #!/bin/bash

#create fh=3 to read from file toread.txt
exec 3<toread.txt

#use fh
cat <&3
# > this is a test

#create fh=4 to write, and write some words
exec 4 > towrite.txt
echo newline test >&4

#to close fh
#generally, shell will close fh as long as you exit script
exec 3>&-
exec 4>&-

      　　

    • ss
    • ss
  • <math> 
    • #!/bin/bash
no1=4;
no2=5;

let result=no1+no2
#no need $ for using let
let no1++
let no1--
let no1+=6
#equal to: let no1=no1+6

result2=$[ no1 + no2]
result22=$[ $no1 + 5]

result3=$(( no1 +1 ))
result33=$(( $no1 +1 ))

result4=`expr $no1+5`

##advanced usage: bc
echo "4*0.33"|bc
#> 1.32
result=`echo "$no1 * 1" |bc`
echo $result
#> 4
echo "scale=2;22/7"|bc
#> 3.14: to set decimal digits to 2
dn=100
bn=1100100
echo "obase=2;$dn"|bc
#> 1100100
echo "obase=10;ibase=2;$bn"|bc
#> 100
echo "sqrt(100)"|bc
#> 10
echo "10^3"|bc
#> 1000

 

  • alias 
    • #!/bin/bash

alias m='more'
unlias m

#\command
#to exec the original command rather than its alias
\m
# > command not found
alias
# > list all alias
  •  tput 
    • #!/bin/bash

##col num & line num
tput cols
tput lines

##current terminal's name
tput longname

##move cursor to (100,100)
tput cup 100 100

##set backgroud color and foreground color
## number can be 1-7 each interger is a specific color
tput setb 7
tput setf 6

##set bold
tput bold

##set unline's start and end
tput smul
tput rmul

##set all contents after current cursor position
##??
tput ed
  • stty
    • to change and print terminal settings
    • #!/bin/bash

##to disable echo in terminal
echo "Enter Password: "
stty -echo
read password
stty echo
echo
echo End Set Password

##to show terminal settings
echo -g
# > 2d00:5:bf:......................
  • date
    • persion is second
    • "+" the format string with prefix + is date's paramter
    • "--date" indicate the date as input
    • %a/%A = Sat/Saturday
    • %b/%B = Nov/Novmber
    • %d/%D = 31(day)/date with specific format, such as 10/11/2020
    • %y/%Y = 20/2020
    • $ date
> Sun Oct 11 07:06:40 PDT 2020
##+<date's parameter>
$ date +%s
> 1602425200
# --date to indicate the date as input
$ date --date "Sat Jan 11 2020" +%s 
> 1578729600
date --date "Jan 11 2020" +%A
> Saturday
date "+%d %b %Y"
> 11 Oct 2020

#set date
$ date -s "12 Oct 2022"
    • #!/bin/bash

start=$(date +%s)
sleep 3
end=$(date +%s)
diff=$((end-start))
echo "diff time is: $diff"
#> 3
  • time
    • to get the time of execuating a command or the resource using by this command
    • #to check how long time a command used
# time cmd|script
# real time: 
#The CPU time consumed by this cmd|script's process. 
# real time = 'this cmd|script's CPU time'+'this cmd|script's block time (eg: time consumed to wait IO)'+'other process's CPU time'
# linux is an multiple process system, while a cmd is executed, it might that some other process's race CPU
# user time: the CPU time exactly consumed by this cmd|script
# system time: the CPU time consumed by kernal system call by this cmd|script

$ time ls
> testfile.sh test.txt ...
> real 0m0.015s
> user 0m0.000s 
> sys 0m0.004s

       

    • fg
    • er
  • <process> 
    • $ pgrep bash
> 8111
$ cat /proc/8111/environ
> USER=aaaHOME=/u/aaaPATH=/bin......
$cat /proc/8111/environ|tr '\0' '\n'
> USER=aaa
HOME=/u/aaa
PATH=/bin
....

 

  • export: export <env_var>: the env_var will get by any procedure launch by current shell  
    • export PATH=/u/test:$PATH
    • function to easier add a PATH
    • prepend() {[ -d "$2" ] && eval $1=\"$2\$\{$1:+':'\$$1\}\" && export $1; }

#usage notes:
#${parameter:+expression}
#if parameter exist and is not empty, then using the value of expression

 

  • [] it is a command 
    • test is similar, but it is not as efficient as [], because test will always launch a new process　
    • if [ $UID -ne 0 ]; then
  echo None root user
else
  echo root user
fi


if test $UID -ne 0
then
....
....
    • sss
    • sss
    • sss
    • ss
    • s
    • s
    • s
posted @ 2020-10-08 19:57  cynn  阅读(81)  评论(0)    收藏  举报