範例與常用技巧

檔頭常用宣告

# quickly syntax
set -euo pipefail

# let script exit if a command fails
set -o errexit 
# OR
set -e

# let script exit if an unsed variable is used
set -o nounset
# OR
set -u

# This setting prevents errors in a pipeline from being masked.
set -o pipefail

# for Debug
set -x

# setting IFS
IFS=$'\n\t'

How set -o pipefail works

$ grep some-string /non/existent/file | sort
grep: /non/existent/file: No such file or directory
$ echo $?
0

$ set -o pipefail
$ grep some-string /non/existent/file | sort
grep: /non/existent/file: No such file or directory
$ echo $?
2

How the IFS  works

#!/bin/bash
names=(
  "Aaron Maxwell"
  "Wayne Gretzky"
  "David Beckham"
  "Anderson da Silva"
)

echo "With default IFS value..."
for name in ${names[@]}; do
  echo "$name"
done

echo ""
echo "With strict-mode IFS value..."
IFS=$'\n\t'
for name in ${names[@]}; do
  echo "$name"
done

############### Output #############
With default IFS value...
Aaron
Maxwell
Wayne
Gretzky
David
Beckham
Anderson
da
Silva

With strict-mode IFS value...
Aaron Maxwell
Wayne Gretzky
David Beckham
Anderson da Silva

檔案的目錄位置

# 指定的檔案
readlink -f <file.name>

# 目前檔案
WORKDIR=$(readlink -f "$0") ;目前檔案的絕對路經
WORKDIR=$( cd $( dirname "$0" ) && pwd )

Script 檔案名稱

$ echo $0
./test.sh

$ echo `basename $0`
test.sh 

刪除 * 天前的舊備份檔

cd $BACKUP_DIR
for backup in `find . -ctime +$BACKUP_KEEP_DAYS -name "cacti.*.tar.gz"`; do rm -f $backup; done;

輸出多行的文字訊息

cat <<EOF
Welcome .....
	
Here are the messages that you want to show up
		
EOF

將執行後的所有輸出訊息導入一個檔案

#!/bin/sh
LOG="my.log"
(
....
) 2>&1 | tee -a $LOG 

不適用在內容裡有 python 指令的訊息輸入，輸入等待的畫面會無法顯示。

temp=$(mktemp)
exec &> ${temp}

echo "All outputs will be saved into the file ${temp}."

快速修改大量檔案的副檔名

## *.old -> *.new
for fname in $(ls *.old);do echo "mv $fname ->"; echo $(echo $fname |sed 's/.old/.new/');mv $fname $(echo $fname | sed 's/.old/.new/');done

快速新增或列出多個指定目錄

mkdir {AAA,BBB,CCC}

快速備份設定檔

cp my.cfg{,.bak}

計算指定目錄底下的檔案總數量

用 find

# 計算目前目錄底下所有檔案數
find . -type f | wc -l 

# 計算第一層所有子目錄的檔案數並排序清單
find . -maxdepth 1 -type d -print0 | xargs -0 -I {} sh -c 'echo $(find {} -type f | wc -l) {}' | sort -n
NOTE: 第一層子目錄名稱不可包含空格 

用 rsync

rsync --stats --dry-run -ax /usr /tmp

Number of files: 326,373 (reg: 211,698, dir: 24,284, link: 90,391)
Number of created files: 326,373 (reg: 211,698, dir: 24,284, link: 90,391)
Number of deleted files: 0
Number of regular files transferred: 211,698
Total file size: 7,180,685,730 bytes
Total transferred file size: 7,178,524,818 bytes

NOTE: 這指令實際不會作檔案複製，/tmp 只是一個假目錄，回傳結果是 reg: 211698 就是檔案總數

用 tree

tree /mydir -a | tail -n 1

5 directories, 56 files

NOTE: 當目錄底下有包含 symbolic link 也會被計算

在 SHELL 內執行另一個外部 SHELL 或指令

1. 使用 pipe line

echo"md5sum $X > $X.sum "| bash

2. 使用 eval

get_arch="uname -p"
if [ "`eval "$get_arch"`" = "i686" ]; then
....
fi 

命令模式提示字元的路徑名稱太長

加上這變數

PROMPT_DIRTRIM=2

處理 CSV 檔

#!/bin/bash
INPUT=data.cvs
OLDIFS=$IFS
IFS=','
[ ! -f $INPUT ] && { echo "$INPUT file not found"; exit 99; }
while read flname dob ssn tel status
do
	echo "Name : $flname"
	echo "DOB : $dob"
	echo "SSN : $ssn"
	echo "Telephone : $tel"
	echo "Status : $status"
done < $INPUT
IFS=$OLDIFS

建立暫存檔

tmpfile1=$(mktemp)
tmpfile2="/tmp/$(basename $0).$$.tmp"

shuf: 隨機排序

curl -s https://www.imdb.com/list/ls020046354/export | cut -d ',' -f 6  | shuf

tree: 顯示專案目錄的檔案樹

tree --dirsfirst --filelimit 10 --sort=name

# Display size of files
tree -s

# Display permissions of files
tree -p

# Display directory only
tree -d

# Display till a certain level/depth
tree -L 1

# List only those files that match pattern given
tree -P *screenshot*

lsof: 偵錯 process/port/NFS

# What process is using the port 50000
lsof -i :50000

# What process is using the mount-point
lsof | grep /path/to/mount-point
lsof +f -- /path/to/dir

# What files and directories are using by the process
lsof -p `pidof <app_name>`

sort : 資料排序

sort -t ',' -k5,5 -k1,1 -k9,9 -k3,3 -k11,11 my.csv

•  -t 分隔符號
• -k5,5 排序第 5 欄，以字串類型排列
• 欄位排序先後依序為第 5, 1, 9, 3, 11 欄
• 欄位排序若要以數值方式來排，改成 -k5,5n

timeout : 自動停止執行

timeout 10 tail -f /var/log/httpd/access.log
timeout 5m ping 8.8.8.8
timeout 300 tcpdump -n -w data.pcap

# Sending specific signal
# To get a list of all available signals, use the command kill -l .
timeout -s SIGKILL ping 8.8.8.8

variables : 變數

變數	說明
$0	腳本檔名
$1	第1個參數
$2	第2個參數
${10}	第10個參數 #10
$#	參數的個數
$*	顯示所有參數 (作為一個字串)
$@	顯示所有參數 (每個為一個獨立字串)
${$*}	傳遞到腳本中的參數的個數
${$@}	傳遞到腳本中的參數的個數
$?	腳本結束後的傳回值
$$	腳本的程序 ID
$_	前個命令的最後一個參數
$!	最後一個執行程序的 ID
u=${1:-root}	如果 $1 未指定，就賦予值 root
u=${USER:-foo}	如果 $USER 未指定，就賦予值 foo
len=${#var}	計算 $var 字串的長度

如果 $2 未指定或空值，輸出錯誤訊息

${varName?Error varName is not defined}
${varName:?Error varName is not defined or is empty}

• Introduction to Bash Shell Parameter Expansions

cut: 切割文字

# AAA = BBB, 取出 BBB
cut -d= -f2

# 111 2222 33 444444 555, 取出 33 以後的所有內容
cut -d ' ' -f3-

# 檢視超長的文字
head -n 1 data.csv | wc  # 計算行的字元數
head data.csv | cut -c -30  # 列出前幾行的前 30 個字元, 如果要顯示後 30 個字元，可以用 30-

完整複製 Home 目錄

由於 User 的 Home 目錄內有許多隱藏檔，若要完整複製它們，有兩個方法：

方法一：可以複製成一個新目錄

cd /home
cp -a user1/ user1_new/

方法二：複製到一個現有目錄內

cd /home
cp -a user1/.[^.]* user1_new/

建立一個新的 Home 目錄

cp -r /etc/skel /home/user1
chown -R user1.group1 /home/user1
chmod 0700 /home/user1 

xargs

接入(Pipe) 不支援 stdin 指令的替代方法

• How to Use the Powerful Xargs Command in Linux

printf: 格式化輸出

• %s 字串
• %d 整數

printf "%-40s ..................%s\n" "Disable the service $1" "[$2]"

Disable the service apmd                 ..................[OK]
Disable the service bluetooth            ..................[OK]
Disable the service hidd                 ..................[OK]
Disable the service cups                 ..................[OK]
Disable the service firstboot            ..................[OK]
Disable the service readahead_early      ..................[OK]

printf "%40s ..................%s\n" "Disable the service $1" "[$2]"

                Disable the service apmd ..................[OK]
           Disable the service bluetooth ..................[OK]
                Disable the service hidd ..................[OK]
                Disable the service cups ..................[OK]
           Disable the service firstboot ..................[OK]
     Disable the service readahead_early ..................[OK] 

印出一個長符號

printf -- '-%.0s' {1..80}
printf -- '=%.0s' {1..80}

ping: 掃描一個 IP 範圍

{ for p in {1..254}; do ping -c1 -w1 10.22.9.$p & done } | grep "64 bytes"

nice: Reduce CPU and Disk load of backup scripts

# Reduce the I/O priority of the /usr/local/bin/backup.sh script so that it does not interfere with other processes
# The -n parameter must be between 0 and 7, where lower numbers mean higher priority
/usr/bin/ionice -c2 -n7 /usr/local/bin/backup.sh

# To reduce the CPU priority, use the command nice
# The -n parameter can range from -20 to 19, where lower numbers mean higher priority
/usr/bin/nice -n 19 /usr/local/bin/backup.sh

# Nice and ionice can also be combined, to run a script at low I/O and CPU priority
/usr/bin/nice -n 19 /usr/bin/ionice -c2 -n7 /usr/local/bin/backup.sh