> bash -x debug.sh 
+ echo 'First line'
First line # 输出结果没有加号
++ date # 先执行命令替换 两个加号是因为该命令嵌套在echo中
+ echo 'Print datetime: Thu 26 Mar 2020 08:21:28 PM CST Done.'
Print datetime: Thu 26 Mar 2020 08:21:28 PM CST Done.

> export PS4='+${BASH_SOURCE}:${LINENO}:${FUNCNAME[0]}: '
> bash -x debug.sh 
+debug.sh:3:: echo 'First line'
First line
++debug.sh:4:: date
+debug.sh:4:: echo 'Print datetime: Thu 26 Mar 2020 08:35:59 PM CST Done.'
Print datetime: Thu 26 Mar 2020 08:35:59 PM CST Done.

trap 'echo "VARIABLE-TRACE> \$variable = \"$variable\""' DEBUG
variable=29
let variable++
let variable*=5
exit 0

# 输出如下
VARIABLE-TRACE> $variable = ""
VARIABLE-TRACE> $variable = "29"
VARIABLE-TRACE> $variable = "30"
VARIABLE-TRACE> $variable = "150"

trap 'echo $BASH_COMMAND' ERR

#!/usr/bin/bash

func1 () {
  for i in `seq 0 3`
  do
    echo -e "Level$i\t  `caller $i`"
  done
}

func2 () {
  func1
}

func3 () {
  func2
}

func3
caller 0 # 必须在函数中调用 否则无输出
exit 0

set -x
date
set +x

> bash script1.sh # 不需要添加调试参数
The script starts now.

+ date
Fri 28 Feb 2020 06:23:04 PM CST
+ set +x

This is a string: black
And this is a number: 9

> set -v
> date
date 
Fri 28 Feb 2020 06:54:47 PM CST
> set -x      # 参数可以累加
date        # -v 的效果
+ date       # -x 的效果
Fri 28 Feb 2020 06:55:37 PM CST
> set +vx      # 取消参数
set +vx

> ls "color: #ff0000">默认调试


也可以直接在脚本第一行添加参数让脚本默认以调试模式启动：


#!/bin/bash -xv


还可以在可能出错的命令前用echo输出调试信息：


echo "debug message: now attempting to start w command"; w # 用 ; 对要执行的命令排序
echo "Variable VARNAME is now set to $VARNAME."


设置选项辅助调试


为了方便调试，我们可以使用set命令对bash的选项进行设置：


> set -o # 查看所有选项的开关状态
> set -o | grep xtrace
xtrace     off
> set -x # 等价于 set -o xtrace
> set -o | grep xtrace 
+ grep --color=auto xtrace
+ set -o
xtrace     on
> set +x # 等价于 set +o xtrace
+ set +x
> set -o | grep xtrace
xtrace     off



常用调试选项


引用为定义变量时报错:


> unset $VAR;echo $VAR

> set -u # 等价于 set -o nounset
> echo $var
bash: var: unbound variable




为防止误操作覆盖文件中的数据, 设置禁止重定向到已经存在的文件:


> set -C # 等价于 set -o noclobber
> touch test
> date > test
bash: test: cannot overwrite existing file



设置不解析通配符:


> set -f # 等价于 set -o noglob
> touch *
> ll *
-rw-rw-r-- 1 remilia remilia 0 Mar 1 20:09 '*'