shell编程 (3) —— 调试

shell编程 (3) —— 调试

shell调试技巧

shell脚本虽然不像高级语言那样有专门的调试工具和调试机制，但是前辈们仍然想出了一些办法来进行shell脚本的错误检测。

trap

shell脚本在执行的时候会产生三伪信号（不是操作系统发出的信号）。我们可以使用trap捕获信号然后进行shell的调试。 shell伪信号的产生：

trap的使用： trap commaond sig1,sig2,… 注：command使用单引号”’”包围的。 例子： code:

#!/bin/bashtrap 'echo "the $LINENO line before executing, a is $a"' DEBUGtime=0a=1while (( $time<6 ))do let "a=a*2" let "time++"done

output:

$ ./two.shthe 3 line before executing, a isthe 4 line before executing, a isthe 5 line before executing, a is 1the 7 line before executing, a is 1the 8 line before executing, a is 2the 5 line before executing, a is 2the 7 line before executing, a is 2the 8 line before executing, a is 4the 5 line before executing, a is 4the 7 line before executing, a is 4the 8 line before executing, a is 8the 5 line before executing, a is 8the 7 line before executing, a is 8the 8 line before executing, a is 16the 5 line before executing, a is 16the 7 line before executing, a is 16the 8 line before executing, a is 32the 5 line before executing, a is 32the 7 line before executing, a is 32the 8 line before executing, a is 64the 5 line before executing, a is 64

这种调适技巧针对递归的作用是有限的： code

trap 'echo "the $LINENO line before executing, a is $a, b is $b"' DEBUGa=120b=250gcd(){ if [ $b -eq 0 ]; then return $a else t=$a a=$b b=`expr $t % $b` gcd $a $b fi}gcd $a $becho "gcd is "$

执行代码

$ ./trap.shthe 3 line before executing, a is , b isthe 4 line before executing, a is 120, b isthe 15 line before executing, a is 120, b is 250the 16 line before executing, a is 10, b is 0gcd is 10

试试ERR： code:

#!/bin/bashtrap 'echo "focus on $LINENO,"$string' ERRstring="here is a error"

执行脚本： （我们将标准错误输出重定向到文件file中）

$ ./trap.sh >&2 2>filefocus on 4,here is a error$ cat file./trap.sh: line 4: ipconfig: command not found

tee

有关tee的解释是这样的： ​​tee - read from standard input and write to standard output and files​​​ tee读入数据，然后产生两支分流，一支是标准输出，另一支输出数据到文件。 一个例子： 查阅本机eth0的mac地址。 它可以用这条语句实现： ​​​cat /etc/sysconfig/network-scripts/ifcfg-eth0 |grep HWADDR |cut -d= -f2​​​ 但是，这看起来有些复杂。。。 我们可以使用tee来跟踪流。 ​​​cat /etc/sysconfig/network-scripts/ifcfg-eth0 | tee -a txt| grep HWADDR |tee -a txt | cut -d= -f2 | tee -a txt​​​ 运行结果：

$ ./tee.sh00:0c:29:e8:97:1b$ cat txtDEVICE=eth0HWADDR=00:0c:29:e8:97:1bTYPE=EthernetUUID=c5857400-a96d-451d-8983-10a52193427cONBOOT=noNM_CONTROLLED=yesBOOTPROTO=dhcpIPADDR=192.168.137.99NETMASK=255.255.0.0IPV6INIT=noUSERCTL=noHWADDR=00:0c:29:e8:97:1b00:0c:29:e8:97:1b

调试钩子

调试钩子的思想有些像C中的条件编译。当我们需要进行中间变量的输出时打开它，否则关闭它。 shell中的调试钩子的格式一般是这样的：

DEBUG(){ if [ "$DEBUG" = "true" ]; then ...

还是那个2^6的例子：

DEBUG(){ if [ "$DEBUG" = "true" ]; then echo "time is $time, a is $a" fi}time=0a=1while (( $time<6 ))do let "a=a*2" let "time++" DEBUG done

执行脚本：

$ export DEBUG="true"; ./debug.sh time is 1, a is 2time is 2, a is 4time is 3, a is 8time is 4, a is 16time is 5, a is 32time is 6, a is 64

shell选项

直接使用指令sh也就是使用bash - GNU Bourne-Again SHell 他们的手册查询结果是一样的。

[edemon@CentOS ~]$ man sh > sh.txt[edemon@CentOS ~]$ man bash > bash.txt[edemon@CentOS ~]$ diff bash.txt sh.txt[edemon@CentOS ~]$

例子：

echo I start to run....if [ 1 -lt 2 ] then echo yesfi

[edemon@CentOS ~]$ ./err.sh I start to run...../err.sh: line 4: syntax error near unexpected token `fi'./err.sh: line 4: `fi'[edemon@CentOS ~]$ bash -n err.sh err.sh: line 4: syntax error near unexpected token `fi'err.sh: line 4: `fi'[edemon@CentOS ~]$ sh -n err.sh err.sh: line 4: syntax error near unexpected token `fi'err.sh: line 4: `fi'

仍然以2^6的我例子来做说明：

#!/bin/bashtrap 'echo "the $LINENO line before executing, a is $a"' DEBUGtime=0a=1while (( $time<6 ))do let "a=a*2" let "time++"done

add ​​-x​​​ to run our program: 在普通语句前面加上’+’，变量已经更新。 在trap debug前面加上“++”

$ bash -x trap_debug.sh + trap 'echo "the $LINENO line before executing, a is $a"' DEBUG++ echo 'the 3 line before executing, a is 'the 3 line before executing, a is + time=0++ echo 'the 4 line before executing, a is 'the 4 line before executing, a is + a=1++ echo 'the 5 line before executing, a is 1'the 5 line before executing, a is 1+ (( 0<6 ))++ echo 'the 7 line before executing, a is 1'the 7 line before executing, a is 1+ let 'a=a*2'++ echo 'the 8 line before executing, a is 2'the 8 line before executing, a is 2+ let time++++ echo 'the 5 line before executing, a is 2'the 5 line before executing, a is 2+ (( 1<6 ))++ echo 'the 7 line before executing, a is 2'the 7 line before executing, a is 2+ let 'a=a*2'++ echo 'the 8 line before executing, a is 4'the 8 line before executing, a is 4+ let time++++ echo 'the 5 line before executing, a is 4'the 5 line before executing, a is 4+ (( 2<6 ))++ echo 'the 7 line before executing, a is 4'the 7 line before executing, a is 4+ let 'a=a*2'++ echo 'the 8 line before executing, a is 8'the 8 line before executing, a is 8+ let time++++ echo 'the 5 line before executing, a is 8'the 5 line before executing, a is 8+ (( 3<6 ))++ echo 'the 7 line before executing, a is 8'the 7 line before executing, a is 8+ let 'a=a*2'++ echo 'the 8 line before executing, a is 16'the 8 line before executing, a is 16+ let time++++ echo 'the 5 line before executing, a is 16'the 5 line before executing, a is 16+ (( 4<6 ))++ echo 'the 7 line before executing, a is 16'the 7 line before executing, a is 16+ let 'a=a*2'++ echo 'the 8 line before executing, a is 32'the 8 line before executing, a is 32+ let time++++ echo 'the 5 line before executing, a is 32'the 5 line before executing, a is 32+ (( 5<6 ))++ echo 'the 7 line before executing, a is 32'the 7 line before executing, a is 32+ let 'a=a*2'++ echo 'the 8 line before executing, a is 64'the 8 line before executing, a is 64+ let time++++ echo 'the 5 line before executing, a is 64'the 5 line before executing, a is 64+ (( 6<6

bash -c 让我们从字符串中读取命令。

$ bash -c "echo \"hello world\""

shell的内部变量： |变量名|意义| |LINENO|行号| |FUNCNAME|函数数组| |ps4|设置提示格式|

练习

codingame —— Onboarding

​​ 大意：外星飞船来了，每一轮都有两只飞船向我们袭来，我们需要击毁最近的那个。

# CodinGame planet is being attacked by slimy insectoid aliens.# <---# Hint:To protect the planet, you can implement the pseudo-code provided in the statement, below the player.# game loopwhile true; do # enemy1: name of enemy 1 read enemy1 # dist1: distance to enemy 1 read dist1 # enemy2: name of enemy 2 read enemy2 # dist2: distance to enemy 2 read dist2 # Write an action using echo # To debug: echo "Debug messages..." >&2 if [ $dist1 -lt $dist2 ]; then result=${enemy1} else result=${enemy2} fi # You have to output a correct ship name to shoot ("Buzz", enemy1, enemy2, ...) echo $resultdone

codingame —— Temperatures

​​ 大意：给出n个气温，求出最接近0的温度。如果有一正一负都最接近0摄氏度，那么输出正整数。

注意下面字符串拆分成数组，求解整数绝对值的方法。

# Auto-generated code below aims at helping you parse# the standard input according to the problem statement.# n: the number of temperatures to analyseread n# temps: the n temperatures expressed as integers ranging from -273 to 5526read tempsarray=(${temps// / }) #(${temps//,/ })表示以逗号拆分dis=6000ans=0for val in ${array[@]}; doif [ ${val#-} -lt $dis ]; thenans=$valdis=${val#-}elif [[ ${val#-} -eq $dis && $val -gt 0 ]]; thenans=$valfidone# Write an action using echo# To debug: echo "Debug messages..." >&2echo $ans

codingame —— ASCII Art

​​ 大意： 输入L，H，old_string, 英文字符表示符。 输出old_string对应的新表示符。 比如：

input45 E # ## ## ## ### ### ## # # ### ## # # # # # ### # ## # ## ## ### # # # # # # # # # # ### ### # # # # # # # # # # # # # # # # # ### # # # # # # # # # # # # # # # # # # # # # # # # ### ## # # # ## ## # # ### # # ## # ### # # # # ## # # ## # # # # # # ### # # # ## # # # # # # # # # # # # # # # # # # # # # # # # # # ## # # # # # # # # ### # # # # # # ## ## ## ### # ## # # ### # # # ### # # # # # # # # # ## # ### # # # # # # ### # Output### # ## # ###

访问字符串中的单个字符，自己暂时仅想到这样的办法：

str="ABCDEF"echo ${#str}for ((i=0;i<${#str};i++)); doecho -e ${str:$i:1}'\c'doneecho ""

[edemon@CentOS workspace]$ ./test.sh6ABCDEF

自己一开始使用C写了一个：

#include #include #include /** * Auto-generated code below aims at helping you parse * the standard input according to the problem statement. **/int main(){ //freopen("read","r",stdin); int L; scanf("%d", &L); int H; scanf("%d", &H); fgetc(stdin); char T[257] = {0}; gets(T); char str[200*1025] = {0}; int i,j,k; for (i = 0; i < H; i++) { char ROW[1025] = {0}; gets(ROW); strcat(str,ROW); } short dex_arr[200] = {0}, len = 0, dex = 0; for(i=0;T[i];i++){ if((T[i]>=65 && T[i]<=90) || (T[i]>=97 && T[i]<=122)){ dex = T[i]-97; if(dex < 0) dex += 32; } else dex = 26; dex_arr[len++] = dex; } //printf("dex len is %d, dex_arr[0] is %d\n",len,dex_arr[0]); for(i=0;i

然后再尝试用bash来写，但是有一个问题，怎么进行两个英文字符的相减操作？字母转成整数？可是怎么转？

# Auto-generated code below aims at helping you parse# the standard input according to the problem statement.read Lread Hread Tstring=""for (( i=0; i how can we sub two letters? if [ $temp -lt 0 ]; then temp=`expr $temp + 32` fi dex[${dex_len}]=$temp dex_len=`expr $dex_len + 1` done#echo ${dex[@]}for (( i=0;i

打印九九乘法表

for (( i=1;i<10;i++ )); do for (( j=1;j<=i;j++ )); do echo -e $j" * "$i" = "`expr $j \* $i`"\t\c" done echo ""done

在test下创建30个目录，并赋予所有者读、写、可执行执行的权限，同组其他人员读、可执行权限，其他人员读的权限。

for (( i=1;i<=30;i++ ));domkdir -p ./test/dir$ichmod -R 754 ./test/dir$idonels -l

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