How To Debug a Running Shell Script
in [Shell]
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From: R. Bernstein on 19 Jun 2008 03:02 A little while back someone asked about debugging a running shell script. (Alas, the post from less than 3 weeks ago has expired in my news reader.) An acceptable solution was proposed which periodically reads a file that controls turning on some debugging switches. Another variation on that idea is to install a signal handler. This has an advantage of not requiring any sort of polling which means the debugging will have a more instantaneous effect, doesn't have to appear in a loop or appear more than once or other than at the beginning of the file. Here's an example. In file debugit.sh: # This is my extra debug hook trap 'set -x' USR1 ; trap 'set +x' USR2 echo $$ while : ; do date=$(date) echo "$date" sleep 2 done Now run: $ bash debugit.sh 9386 Thu Jun 19 02:31:09 EDT 2008 Thu Jun 19 02:31:11 EDT 2008 From some other shell: kill -USR1 9386 And back to the running program... (debugit.sh:5): - [4,0] : ((debugit.sh:6): - [4,1] date (debugit.sh:6): - [4,0] date='Thu Jun 19 02:31:19 EDT 2008' (debugit.sh:7): - [4,0] echo 'Thu Jun 19 02:31:19 EDT 2008' Thu Jun 19 02:31:19 EDT 2008 (debugit.sh:8): - [4,0] sleep 2 (debugit.sh:5): - [4,0] : ((debugit.sh:6): - [4,1] date (debugit.sh:6): - [4,0] date='Thu Jun 19 02:31:21 EDT 2008' (debugit.sh:7): - [4,0] echo 'Thu Jun 19 02:31:21 EDT 2008' Thu Jun 19 02:31:21 EDT 2008 (debugit.sh:8): - [4,0] sleep 2 ((debugit.sh:9): - [4,0] To turn off debugging: kill -USR2 9386 set +x Thu Jun 19 02:31:23 EDT 2008 Thu Jun 19 02:31:25 EDT 2008 ... In the above listing, my bash-specific PS4 setting is: declare -x PS4="(\${BASH_SOURCE}:\${LINENO}): \${FUNCNAME[0]} - [\${SHLVL},\${BASH_SUBSHELL}]\\n" This works best for version 3.0 and above. Going further, if you've got the bash debugger (http://bashdb.sf.net) installed, it comes with a hook to allow it to get called when an interrupt is given to the program. Find the file bashdb-trace installed on your system. On my Ubuntu box, Debian bashdb package installs it in /usr/share/bashdb/bashdb-trace. Now change your program like this: # This is my extra debug hook source /usr/share/bashdb/bashdb-trace echo $$ while : ; do date=$(date) echo "$date" sleep 2 done And run: bash ./debugit2.sh Bourne-Again Shell Debugger, release bash-3.1-0.08 Copyright 2002, 2003, 2004, 2006 Rocky Bernstein This is free software, covered by the GNU General Public License, and you are welcome to change it and/or distribute copies of it under certain conditions. 9435 Thu Jun 19 02:43:06 EDT 2008 Thu Jun 19 02:43:08 EDT 2008 Sent it an "interrupt" signal kill -INT 9435 And back to the running program: Program received signal SIGINT (2)... ->0 in file `./debugit2.sh' at line 251 # not sure where 251 came from! ##1 main() called from file `./debugit2.sh' at line 0 bashdb<0> where ->0 in file `./debugit2.sh' at line 9 # but this line number is now right ##1 main() called from file `./debugit2.sh' at line 0 bashdb<1> list 1 1: # This is my extra debug hook 2: source /usr/share/bashdb/bashdb-trace 3: 4: echo $$ 5: while : ; do 6: date=$(date) 7: echo "$date" 8: sleep 2 9:==>done bashdb<2> s (./debugit2.sh:5): 5: while : ; do bashdb<3> s (./debugit2.sh:6): 6: date=$(date) bashdb<4> Some of this is described in the bashdb manual: http://bashdb.sourceforge.net/bashdb.html#SEC10 The hooks and the debugger in general are not as robust as I would like -- feel free to contribute!
From: invincible on 20 Jun 2008 08:58 On 19 Jun, 08:02, ro...(a)panix.com (R. Bernstein) wrote: > A little while back someone asked about debugging a running shell > script. (Alas, the post from less than 3 weeks ago has expired in my > news reader.) > > An acceptable solution was proposed which periodically reads a file > that controls turning on some debugging switches. > > Another variation on that idea is to install a signal handler. This > has an advantage of not requiring any sort of polling which means the > debugging will have a more instantaneous effect, doesn't have to > appear in a loop or appear more than once or other than at the beginning > of the file. > > Here's an example. In file debugit.sh: > > # This is my extra debug hook > trap 'set -x' USR1 ; trap 'set +x' USR2 > > echo $$ > while : ; do > date=$(date) > echo "$date" > sleep 2 > done > > Now run: > > $ bash debugit.sh > 9386 > Thu Jun 19 02:31:09 EDT 2008 > Thu Jun 19 02:31:11 EDT 2008 > > From some other shell: > kill -USR1 9386 > > And back to the running program... > > (debugit.sh:5): - [4,0] > : > ((debugit.sh:6): - [4,1] > date > (debugit.sh:6): - [4,0] > date='Thu Jun 19 02:31:19 EDT 2008' > (debugit.sh:7): - [4,0] > echo 'Thu Jun 19 02:31:19 EDT 2008' > Thu Jun 19 02:31:19 EDT 2008 > (debugit.sh:8): - [4,0] > sleep 2 > (debugit.sh:5): - [4,0] > : > ((debugit.sh:6): - [4,1] > date > (debugit.sh:6): - [4,0] > date='Thu Jun 19 02:31:21 EDT 2008' > (debugit.sh:7): - [4,0] > echo 'Thu Jun 19 02:31:21 EDT 2008' > Thu Jun 19 02:31:21 EDT 2008 > (debugit.sh:8): - [4,0] > sleep 2 > ((debugit.sh:9): - [4,0] > > To turn off debugging: > kill -USR2 9386 > > set +x > Thu Jun 19 02:31:23 EDT 2008 > Thu Jun 19 02:31:25 EDT 2008 > ... > > In the above listing, my bash-specific PS4 setting is: > > declare -x PS4="(\${BASH_SOURCE}:\${LINENO}): \${FUNCNAME[0]} - [\${SHLVL},\${BASH_SUBSHELL}]\\n" > > This works best for version 3.0 and above. > > Going further, if you've got the bash debugger (http://bashdb.sf.net) > installed, it comes with a hook to allow it to get called when an > interrupt is given to the program. Find the file bashdb-trace > installed on your system. On my Ubuntu box, Debian bashdb package > installs it in /usr/share/bashdb/bashdb-trace. Now change your program > like this: > > # This is my extra debug hook > source /usr/share/bashdb/bashdb-trace > > echo $$ > while : ; do > date=$(date) > echo "$date" > sleep 2 > done > > And run: > > bash ./debugit2.sh > Bourne-Again Shell Debugger, release bash-3.1-0.08 > Copyright 2002, 2003, 2004, 2006 Rocky Bernstein > This is free software, covered by the GNU General Public License, and you are > welcome to change it and/or distribute copies of it under certain conditions. > > 9435 > Thu Jun 19 02:43:06 EDT 2008 > Thu Jun 19 02:43:08 EDT 2008 > > Sent it an "interrupt" signal > kill -INT 9435 > > And back to the running program: > > Program received signal SIGINT (2)... > ->0 in file `./debugit2.sh' at line 251 # not sure where 251 came from! > ##1 main() called from file `./debugit2.sh' at line 0 > bashdb<0> where > ->0 in file `./debugit2.sh' at line 9 # but this line number is now right > ##1 main() called from file `./debugit2.sh' at line 0 > bashdb<1> list 1 > 1: # This is my extra debug hook > 2: source /usr/share/bashdb/bashdb-trace > 3: > 4: echo $$ > 5: while : ; do > 6: date=$(date) > 7: echo "$date" > 8: sleep 2 > 9:==>done > bashdb<2> s > (./debugit2.sh:5): > 5: while : ; do > bashdb<3> s > (./debugit2.sh:6): > 6: date=$(date) > bashdb<4> > > Some of this is described in the bashdb manual:http://bashdb.sourceforge.net/bashdb.html#SEC10 > > The hooks and the debugger in general are not as robust as I would > like -- feel free to contribute! Thats was me and many thanx for your help. I would come back to you soon on this. Ciao
From: mop2 on 20 Jun 2008 20:30 On Fri, 20 Jun 2008 09:58:41 -0300, invincible <imanuk2007(a)googlemail.com> wrote: > On 19 Jun, 08:02, ro...(a)panix.com (R. Bernstein) wrote: >> A little while back someone asked about debugging a running shell >> script. (Alas, the post from less than 3 weeks ago has expired in my >> news reader.) >> >> An acceptable solution was proposed which periodically reads a file >> that controls turning on some debugging switches. >> >> Another variation on that idea is to install a signal handler. This >> has an advantage of not requiring any sort of polling which means the >> debugging will have a more instantaneous effect, doesn't have to >> appear in a loop or appear more than once or other than at the beginning >> of the file. >> >> Here's an example. In file debugit.sh: >> >> # This is my extra debug hook >> trap 'set -x' USR1 ; trap 'set +x' USR2 >> >> >> From some other shell: >> kill -USR1 9386 >> >> >> To turn off debugging: >> kill -USR2 9386 >> > > Thats was me and many thanx for your help. I would come back to you > soon on this. > > Ciao > Hi, another idea using ^C - = q (set -x, set +x, exit) trap 'read -n1 a;case "$a" in q)exit;;-)set -x;;=)set +x;esac' 2
From: R. Bernstein on 22 Jun 2008 00:17 mop2 <invalid(a)mail.address> writes: > Hi, > another idea using ^C - = q (set -x, set +x, exit) > > trap 'read -n1 a;case "$a" in q)exit;;-)set -x;;=)set +x;esac' 2 This is cool. I'd probably add a prompt before the read, and the -n1 option doesn't seem to be in POSIX (for those of you who use dash/ash). More serious though is that one may or may not have access to stdin, e.g. if your script is running as a daemon. So the other code may still be preferable in that kind of situation. And here's yet another variation which eliminates the need to modify the script. Put the following in a file, say "debug_wrapper": # adjust trap as suggested above trap 'set -x' USR1 ; trap 'set +x' USR2 source "$@" Then run run your program: debug_wrapper my_program With all of the variation given, you have an instant debugger. ;-) But there are a couple of thing problems of the "source" method. If the program you are running uses $0 it will report your debug_wrapper rather than itself. Probably in the next release of bashdb I'll add a built-in command to set $0; bashdb or such a wrapper above could then use that to hide itself a little bit more. Second, the stack nesting will be a little different. In another posting I showed how you could tell if your program was source'd or not and this change will confuse something like this.
From: invincible on 26 Jun 2008 12:01
Hello R.Bernstein, Just wanted to know if the above explantion is just valid on bash shell. as I currently operate on Korn . Ciao |