Linux Shells

default.md

Useful Syntax in Shell

#!/bin/bash

#. ./header.sh
#source ./header.sh

echo `date` # print date
printf "Hello, Shell\n"

echo "file：$0";
echo "parameter count: $#";
echo "parameter string: $*";
echo "first parameter：$1";
echo "second parameter：$2";
echo "file content" > filename

## print
user="Bendy Zhang"
age=100
readonly user
echo $user
echo "welcome ${user}"
echo "user length is ${#user}"
echo "cut string: ${user:1:4}"
printf "Hello, %-15s \n" $user   # Hello,    Bendy Zhang
unset age  # you can not unset readonly variable

## if then elif fi
num1=100
num2=100
if test $[num1] -eq $[num2]
then
    echo '=='
else
    echo '!='
fi

# LOOP
for file in `ls /etc`; do
  echo $file
done

for skill in Ada Coffe Action Java; do
    echo "I am good at ${skill}Script"
done

int=1
while(( $int<=5 ))
do
    echo $int
    let "int++"
done

## array
array_name=("bing" "zhang" 100 1)
array_name[0]="Bing"
array_name[3]="str"
echo ${array_name[@]} # print all elements
length=${#array_name[@]}  # array length
length=${#array_name[*]}  # array length

## expression
val=`expr 2 + 2`
echo "sum: $val"

## File (-e)
FILE=/tmp/foo.txt
if [ ! -f "$FILE" ]
then
    echo "File $FILE does not exist"
fi
DIR=/tmp/dir
if [ -d "$DIR" ]
then
    cp -a /source/* $DIR
fi
#mkdir -p $DIR  # create all directories

RUN

chmod +x ./demo.sh
./demo.sh
bash -x demo.sh # debug

File test operators

-b FILE FILE exists and is block special

-c FILE FILE exists and is character special

-d FILE FILE exists and is a directory

-e FILE FILE exists

-f FILE FILE exists and is a regular file

-g FILE FILE exists and is set-group-ID

-G FILE FILE exists and is owned by the effective group ID

-h FILE FILE exists and is a symbolic link (same as -L)

-k FILE FILE exists and has its sticky bit set

-L FILE FILE exists and is a symbolic link (same as -h)

-O FILE FILE exists and is owned by the effective user ID

-p FILE FILE exists and is a named pipe

-r FILE FILE exists and read permission is granted

-s FILE FILE exists and has a size greater than zero

-S FILE FILE exists and is a socket

-t FD
file descriptor FD is opened on a terminal

-u FILE FILE exists and its set-user-ID bit is set

-w FILE FILE exists and write permission is granted

-x FILE FILE exists and execute (or search) permission is granted

syntax

if [ operator FileName ]
then
     echo "FileName - Found, take some action here"
else
   echo "FileName - Not found, take some action here"
fi

DATE

date.sh

#!/bin/bash

DAY=`date '+%m'`
HOUR=`date '+%H'`
HAS_ARGS=false
SERVER="<date server>"

usage() {
	echo "USAGE(Example): setDate -d 10 -h 23"
	echo "sync date from ${SERVER}..."
	ntpdate ${SERVER}
	echo "done."
	exit 1;
}

while getopts d:h: o; do
	case "$o" in
		d)
			DAY=${OPTARG}
			HAS_ARGS=true
			;;
		h)
			HOUR=${OPTARG}
			HAS_ARGS=true
			;;
	esac
done

shift $OPTIND-1

if !(${HAS_ARGS}); then
	usage
else
	echo "current date: "`date`
	d1=`date '+%m'`
	d2=`date '+%M%Y'`
	d="${d1}${DAY}${HOUR}${d2}"
	echo "set date to ${d}..."
	date $d
	echo "current date: "`date`
fi

./date.sh -d <day> [-h <hour>]
./date.sh   // sync date with <date server>

COPY

cp -R /source /dist  # copy source folder and all chilren to dist folder
cp -R /source/. /dist # copy all files in source folder to dist folder
\cp -f /source/. /dist # copy files with disabled the overwrite hint

CRON

auto-sync.cron

0 0 * * * cd "/opt/git-workspace/github.js" && npm run pull:gists && cd "/opt/git-workspace/bndy.net" && git pull && \cp -R -f ../github.js/temp/blog/. ./_posts/ && git add . && git commit -m "auto-sync gists" && git push >/dev/null 2>&1

crontab auto-sync.cron	# append the job in auto-sync.cron file to list
crontab -l  # list curent user jobs
crontab -e  # edit all current user jobs, you can remove or edit the jobs

MISC

scp <file to copy> root@<ip>:/<dest folder>
traceroute <ip/domain>