bash技巧¶
bash的一些技巧
变量子串¶
替换运算符¶
$(varname:-word) 如果varname存在且非null，则返回其值；否则，返回word。
用途：如果变量未定义，则返回默认值。
范例：如果count未定义，则$(count:-0)的值为0
获取参数=后面的内容¶
[root@web01 ~]# echo "--basedir=/applica" | sed -e 's/^[^=]*=//'
/applica
创建只含小写字母的随机数¶
openssl rand -base64 48|sed 's#[^a-z]##g'
调试¶
set -x 调试当前窗口命令
set +x 取消调试
set -e 脚本中有一条命令返回值不为零就退出脚本，可使用test，当前面脚语句执行失败的时候，执行后面的语句
删除无效软链接¶
方法1.
for f in $(find $1 -type l); do [ -e $f ] && rm -f $f; done
方法2.
symlinks -d
symlinks: scan/change symbolic links - v1.2 - by Mark Lord
Usage: symlinks [-crsv] dirlist
Flags: -c == change absolute/messy links to relative
-d == delete dangling links
-r == recurse into subdirs
-s == shorten lengthy links (only displayed if -c not specified)
-v == verbose (show all symlinks)
统计每个文件夹占用的inode总数¶
find */ -exec stat -c "%n %i" {} \; | awk -F "[/ ]" '{if(! a[$1-$NF]++) l[$1]++}END{for (i in l) print i,l[i]}'
拼接时间¶
for n in 20 21
do
for m in {00..59}
do
echo "$n:$m"
done
done
xargs 处理文件名带空格的方法¶
# 使用 -i 参数 '{}'
xargs -i sed -i '/^<extoc>/d;2a<extoc></extoc>\n' '{}'
# 示例
find . -type f -name "*.md" ! -path "./README.md" -a ! -path "./SUMMARY.md"|xargs -i sed -i '/^<extoc>/d;2a<extoc></extoc>\n' '{}'
指定行插入文本内容¶
# 知道行号用以下方法插入
sed -i '88 r b.file' a.file #在a.file的第88行插入文件b.txt
awk '1;NR==88{system("cat b.file")}' a.file >c.file
## 如果不知道行号，用正则匹配
sed -i '/regex/ r b.txt' a.txt
awk '/target/{system("cat b.txt")}' a.txt > c.txt
大小写转换¶
awk '{print toupper($0)}' <<< 'this is a dog!'
# toupper()
# tolower()
# 全文大小写转换
tr a-z A-Z
tr A-Z a-z
# 大小写互换
echo "aBcDE" | tr '[a-zA-Z]' '[A-Za-z]'
示例
比如说：a.txt b.txt c.txt
更名变成 A.txt B.txt C.txt
ls *.txt|sed -nr 's/(.)(\..*)/mv & \u\1\2/e'
[解析]
\u 是转换后面的内容第一个字母为大写，\U是全部为大写直到遇到 \E 为止。这就是区别：
echo 'abc'|sed 's/^../\u&/'
Abc
echo 'abc'|sed 's/^../\U&\E/'
ABc
把每个单词的第一个字母替换成大写¶
this is a dog!
➜ ~ sed 's/\b[a-z]/\u&/g' <<< 'this is a dog!'
This Is A Dog!
# \b大家应该知道是锚定的意思，说白了就是边界符，那么这就只会匹配第一个开头的字母，然后\U的意思在元字符里的解释是“大写（不是标题首字符）\E 以前的字符”，而\u只是将下一个字符变为大写，注意它们的区别噢。
把URL中的大写字符替换成小写¶
http://www.a.com/aaafkslafjlxcv/fsfa/8/Xxxx.XxXX
sed 's/[A-Z]/\l&/g' <<< 'http://www.a.com/aaafkslafjlxcv/fsfa/8/Xxxx.XxXX'
# 同理\L的意思是使之变为小写。
$RANDOM 的范围是 [0, 32767]¶
第二章¶
判断技巧¶
[ -d /abc ] || mkdir -p /abc
创建随机密码方法¶
echo $RANDOM|md5sumopenssl rand -base64 48expect mkpasswdmkpasswd -l 10
date +%N|sha512sumhead /dev/urandom|md5sumuuidgen|md5sum- 加密可以使用
md5sum、sha512sum等等，加密之前可以添加一个干扰码，例如：echo yjj$RANDOM|md5sum
- 加密可以使用
创建10个随机字母¶
echo $RANDOM|sha512sum|sed 's#[0-9]##g'|cut -c1-10
变量子串使用技巧¶
生成随机密码¶
[root@db ~]# cat pass.sh
#!/bin/bash
# Password will consist of alphanumeric characters.
MATRIX="0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz.,?@#$%^&*()"
# length of password.
LENGTH="20"
while [ "${n:=1}" -le "$LENGTH" ]
do
PASS="$PASS${MATRIX:$(($RANDOM%${#MATRIX})):1}"
let n+=1
done
echo "$PASS" # ==> Or, redirect to a file, as desired.
exit 0
判断用户输入是否为数字¶
read -p "Please enter the amount of recharge: " re
if [ -n "${re//[0-9]/}" ];then
echo "input error"
continue
fi
# 删除数字进行判断，判断是否为空
# ---
# 方法1：将数字以外的字符替换成空，如果跟本身相同，说明用户输入为数字
[root@yjj ~]# [ "`echo 1231|sed -r 's#[^0-9]##g'`" = "1231" ]&&echo 0||echo 1
0
[root@yjj ~]# [ "`echo 123a|sed -r 's#[^0-9]##g'`" = "123a" ]&&echo 0||echo 1
1
# 方法2：使用expr，如果命令返回结果非零，则表示用户输入的不是数字
[root@yjj ~]# expr 1 + a &>/dev/null
[root@yjj ~]# echo $?
2
计算字符串长度¶
string="I love you"
方法一：
echo ${#string}
方法二：
echo ${string}|wc -L
方法三：
expr length "${string}"
方法四：
awk '{print length($0)}' <<<$string
awk '{print length}' <<<$string ## $0可以省略
方法五:
functions内置函数，strstr
# returns OK if $1 contains $2
strstr() {
[ "${1#*$2*}" = "$1" ] && return 1
return 0
}
命令拼接¶
[root@web 11]# chkconfig |awk '$1!~/crond|sshd|sysstat|network|rsyslog/{print "chkconfig",$1,"off"}'|bash
计算1+2+3+4+5+6+7+8+9+10¶
[root@web scripts]# seq 10|awk '{a+=$1;b=b$1"+"}END{sub("+$","",b);print b"="a}'
1+2+3+4+5+6+7+8+9+10=55
打印下面语句中字符数小于6的单词¶
[root@db ~]# echo Whatever is worth doing is worth doing well.
Whatever is worth doing is worth doing well.
[root@db ~]# echo Whatever is worth doing is worth doing well.|awk 'END{for(i=1;i<=NF;i++)if(length($i)<6) print $i }'
is
worth
doing
is
worth
doing
well.
[root@db ~]# awk 'END{for(i=1;i<=NF;i++)if(length($i)<6) print $i }' <<< "Whatever is worth doing is worth doing well."
[root@db ~]# cat test.sh
for n in Whatever is worth doing is worth doing well.
do
if [ ${#n} -lt 6 ];then
echo $n
fi
done
[root@db ~]# cat test1.sh
for n in Whatever is worth doing is worth doing well.
do
if [ "$n" = "${n:0:6}" ];then
echo $n
fi
done
使用eval实现动态变量¶
用变量值作新的变量名
➜ ~ refer_504_09="123"
➜ ~ time=`date +%H`
➜ ~ echo $time
09
➜ ~ echo $refer_504_09
123
➜ ~ a=`eval echo '$refer_504_'"$time"`
➜ ~ echo $a
123
乘法口诀表¶
awk 'BEGIN{for(i=1;i<=9;i++){for(j=1;j<=i;j++){printf j"*"i"="i*j"\t"}printf "\n"}}'
echo -ne "\033[47;30m`awk 'BEGIN{for(i=1;i<=9;i++){for(j=1;j<=i;j++){printf j"*"i"="i*j"\t"}printf "\n"}}'`\033[0m\n"
seq 9 | sed 'H;g' | awk -v RS='' '{for(i=1;i<=NF;i++)printf("\033[47;30m%dx%d=%d%s", i, NR, i*NR, i==NR?"\033[0m\n":"\t")}'
echo -e "\e[44;37;5m `awk 'BEGIN{for(i=1;i<10;i++) {for(k=1;k<=i;k++) {printf "%d%s%d%s%;}printf "\n"}}'` \e[0m "
for i in {1..9}; do for j in `seq 1 $i`; do echo -ne "\033[47;30m${j}*${i}=$((j*i))\033[0m \t"; done; echo; done
for((i=1;i<10;i++));do for((j=1;j<=i;j++))do printf "$j*$i=$((i*j))\t" ;done;printf "\n";done
圆周率计算¶
➜ ~ echo "scale=1000; a(1)*4" | bc -l
3.141592653589793238462643383279502884197169399375105820974944592307\
81640628620899862803482534211706798214808651328230664709384460955058\
22317253594081284811174502841027019385211055596446229489549303819644\
28810975665933446128475648233786783165271201909145648566923460348610\
45432664821339360726024914127372458700660631558817488152092096282925\
40917153643678925903600113305305488204665213841469519415116094330572\
70365759591953092186117381932611793105118548074462379962749567351885\
75272489122793818301194912983367336244065664308602139494639522473719\
07021798609437027705392171762931767523846748184676694051320005681271\
45263560827785771342757789609173637178721468440901224953430146549585\
37105079227968925892354201995611212902196086403441815981362977477130\
99605187072113499999983729780499510597317328160963185950244594553469\
08302642522308253344685035261931188171010003137838752886587533208381\
42061717766914730359825349042875546873115956286388235378759375195778\
18577805321712268066130019278766111959092164201988
批量修改文件名¶
awk、sed、rename批量修改文件名
源文件名：
stu_102999_1_hello.jpg
stu_102999_2_hello.jpg
stu_102999_3_hello.jpg
stu_102999_4_hello.jpg
stu_102999_5_hello.jpg
修改后：
stu_102999_1_.jpg
stu_102999_2_.jpg
stu_102999_3_.jpg
stu_102999_4_.jpg
stu_102999_5_.jpg
使用awk，gsub
ls|awk '{print "mv "$0,$0}'|awk '{gsub("_hello","",$3)}1'
ls|awk 'BEGIN{ORS=""}{print "mv",$0" ";gsub("_hello","",$0);print $0"\n"}'
ls|awk '{$3=$2=$1;$1="mv";sub("_hello","",$3)}1'
直接使用print拼接
使用sed命令拼接
使用rename批量修改
其他¶
- 环境变量的定义放到 /etc/bashrc #最后执行，不会被覆盖
文件字符集转换方法¶
iconv -f gb2312 -t UTF-8 2.html -o 2.utf8.html
[root@centos scripts]# iconv --help
Usage: iconv [OPTION...] [FILE...]
Convert encoding of given files from one encoding to another.
Input/Output format specification:
-f, --from-code=NAME encoding of original text
-t, --to-code=NAME encoding for output
Information:
-l, --list list all known coded character sets
Output control:
-c omit invalid characters from output
-o, --output=FILE output file
-s, --silent suppress warnings
--verbose print progress information
-?, --help Give this help list
--usage Give a short usage message
-V, --version Print program version
Mandatory or optional arguments to long options are also mandatory or optional
for any corresponding short options.
For bug reporting instructions, please see:
<http://www.gnu.org/software/libc/bugs.html>.