第161页 | Learning the Bash Shell | 阅读 ‧ 电子书库

A Sample bashdb Session

Now we'll show a transcript of an actual session with bashdb, in which the guinea pig is the solution to Task 6-1, the script ndu. Here is the transcript of the debugging session:

[bash]$ bashdb ndu
bash Debugger version 1.0
Stopped at line 0
bashdb> ds
1:     for dir in ${*:-.}; do
2:       if [ -e $dir ]; then
3:         result=$(du -s $dir | cut -f 1)
4:         let total=$result*1024
5:    
6:         echo -n "Total for $dir = $total bytes"
7:    
8:         if [ $total -ge 1048576 ]; then
9:           echo " ($((total/1048576)) Mb)"
10:         elif [ $total -ge 1024 ]; then
11:           echo " ($((total/1024)) Kb)"
12:         fi
13:       fi
14:     done
bashdb> s
Stopped at line 2
bashdb> bp 4
Breakpoint set at line 4
bashdb> bp 8
Breakpoint set at line 8
bashdb> bp 11
Breakpoint set at line 11
bashdb> ds
1:     for dir in ${*:-.}; do
2:  >    if [ -e $dir ]; then
3:         result=$(du -s $dir | cut -f 1)
4:*        let total=$result*1024
5:    
6:         echo -n "Total for $dir = $total bytes"
7:    
8:*        if [ $total -ge 1048576 ]; then
9:           echo " ($((total/1048576)) Mb)"
10:         elif [ $total -ge 1024 ]; then
11:*          echo " ($((total/1024)) Kb)"
12:         fi
13:       fi
14:     done
bashdb> g
Reached breakpoint at line 4
bashdb> !echo $total
6840032
bashdb> cb 8
Breakpoint cleared at line 8
bashdb> ds
1:     for dir in ${*:-.}; do
2:       if [ -e $dir ]; then
3:         result=$(du -s $dir | cut -f 1)
4:* >      let total=$result*1024
5:    
6:         echo -n "Total for $dir = $total bytes"
7:    
8:         if [ $total -ge 1048576 ]; then
9:           echo " ($((total/1048576)) Mb)"
10:         elif [ $total -ge 1024 ]; then
11:*          echo " ($((total/1024)) Kb)"
12:         fi
13:       fi
14:     done
bashdb> bp
Breakpoints at lines: 4 11
Break on condition:
    
bashdb> !total=5600
bashdb> g
Total for . = 5600 bytes (5 Kb)
Reached breakpoint at line 11
bashdb> cb
All breakpoints have been cleared
bashdb> ds
1:     for dir in ${*:-.}; do
2:       if [ -e $dir ]; then
3:         result=$(du -s $dir | cut -f 1)
4:         let total=$result*1024
5:    
6:         echo -n "Total for $dir = $total bytes"
7:    
8:         if [ $total -ge 1048576 ]; then
9:           echo " ($((total/1048576)) Mb)"
10:         elif [ $total -ge 1024 ]; then
11:  >        echo " ($((total/1024)) Kb)"
12:         fi
13:       fi
14:     done
bashdb> g
[bash]$

First, we display the script with ds and then perform a step, taking execution to line 2 of ndu. We then set breakpoints at lines 4, 8, and 11 and display the script again. This time the breakpoints are clearly marked by asterisks (*). The right angle bracket (>) indicates that line 2 was the most recent line executed.

Next, we continue execution of the script that breaks at line 4. We print out the value of total now and decide to clear the breakpoint at line 8. Displaying the script confirms that the breakpoint at line 8 is indeed gone. We can also use the bp command, and it too shows that the only breakpoints set are at lines 4 and 11.

At this stage we might decide that we want to check the logic of the if branch at line 11. This requires that $total be greater than or equal to 1,024, but less than 1,048,576. As we saw previously, $total is very large, so we set its value to 5,600 so that it will execute the second part of the if and continue execution. The script enters that section of the if correctly, prints out the value, and stops at the breakpoint.

To finish off, we clear the breakpoints, display the script again, and then continue execution, which exits the script.