backtick operator

spjcr has asked for the wisdom of the Perl Monks concerning the following question:

Dear Monks, I am completely stumped with this one. Any thoughts would be greatly appreciated!

/:perl -v

This is perl, v5.8.8 built for x86_64-linux-thread-multi
[download]

My script is called from a wrapper script:

} elsif ($stepType eq 'pl') {
     $rc = system("perl $cwd/bin/$step -config=$configFile");
}
[download]

The function in question looks like (i think the issue is around line 247):

sub dbConnect(){
238    my ($dbName) = @_;
239    my ($dbh,$dbUser,$dbPass);
240    my $tempStr;
241
242    LogStatus "Retrieving $dbName login info";
243
244    $tempStr = `pwd`;
245    LogStatus "tempStr1: $tempStr";
246
247    $tempStr = `/prod/scripts/getDBlogin abc01`;
248    LogStatus "tempStr: $tempStr";
249    #($dbUser,$dbPass) = split(/\s/,`/prod/scripts/getDBlogin "$dbN
+ame"`);
250    ($dbUser,$dbPass) = split(/\s/, $tempStr);
251    LogStatus "User for $dbName is $dbUser";
252
253    die "$0: Could not find password for $dbUser" unless(defined($d
+bPass));
254
255    $dbh = DBI->connect("dbi:DB2:$dbName", $dbUser, $dbPass, {AutoC
+ommit=> 0, RaiseError => 1})
256       || die "Can't connect to $database: $DBI::errstr";
257
258    LogStatus "Connected to $dbName as $dbUser";
259
260    return $dbh;
261 }
[download]

The getDBlogin script looks like:

  1 #!/bin/ksh
  2
  3 dbname=$1
  4 idfl=~/$$.idfl
  5 grep -i "$dbname " ~/.passwd > $idfl
  6 userid=$(cut -f2 -d" " $idfl)
  7 pswrd=$(cut -f3 -d" " $idfl)
  8
  9 rm $idfl
 10
 11 print "$userid $pswrd"
[download]

The log looks like:

365 [2010-05-12 15:12:13] ============================================
+=============
366 [2010-05-12 15:12:13]  Script:      create_amb_model
367 [2010-05-12 15:12:13]  Process Id:  30199
368 [2010-05-12 15:12:13]  Start time:  Wed May 12 15:12:13 2010
369 [2010-05-12 15:12:13] ============================================
+=============
370 [2010-05-12 15:12:13]
371 [2010-05-12 15:12:13] DDS AMB Model Creation Starting
372 [2010-05-12 15:12:13] Job name: create_amb_model
373 [2010-05-12 15:12:13] Job config:       /jobs/dds/create_amb_model
+/config/job.config
374 [2010-05-12 15:12:13] Options: 1
375 [2010-05-12 15:12:13] executing step 1 (dds_prod_pg_load.pl)
376 [2010-05-12 15:12:13] Configuration details:
377 [2010-05-12 15:12:13]    Config file:   /jobs/dds/create_amb_model
+/config/job.config
378 [2010-05-12 15:12:13]    Days back:     365
379 [2010-05-12 15:12:13]    Database:      abc01
380 [2010-05-12 15:12:13] Retrieving abc01 login info
381 [2010-05-12 15:12:13] tempStr1: /jobs/dds/create_amb_model
382 [2010-05-12 15:12:16] Run job has FAILED
383 [2010-05-12 15:12:16] ERROR:
384 [2010-05-12 15:12:16]
385 [2010-05-12 15:12:16] ============================================
+=============
386 [2010-05-12 15:12:16]  Process Id:    30199
387 [2010-05-12 15:12:16]  End time:      Wed May 12 15:12:16 2010
388 [2010-05-12 15:12:16]  Elapsed time:  3 seconds
389 [2010-05-12 15:12:16]  CPU time:      0.08 seconds
390 [2010-05-12 15:12:16] ============================================
+=============
[download]

So I am never seeing the second log entry after line 381 in the log where I would expect to see the output from getDBlogin. When I execute the script from the command line I am seeing the correct output. It appears that something unexpected is happening around line 247 in dbConnect(). At line 382 in the log I Ctrl-C the process - otherwise it would just hang; this kills the forked process which causes the wrapping script to log out 'Run job has FAILED' when it sees a non-zero return code. I am happy to provide more information if needed. Thanks in advance!

Comment on backtick operator Select or Download Code

Replies are listed 'Best First'.
Re: backtick operator by JavaFan (Canon) on May 13, 2010 at 15:22 UTC
When I execute the script from the command line I am seeing the correct output. Does this message means it's failing in some other environment? Some environment you're not telling us about? Perhaps a web server? Something else? `grep -i "$dbname " ~/.passwd > $idfl` [download] Are you sure this is looking in the right home directory?	[reply] [d/l]
Re^2: backtick operator by spjcr (Initiate) on May 13, 2010 at 17:00 UTC
Yes, it looks like it is executing in the right home directory - I am executing the script as the same userid and same environment in both instances. The file (.passw) in the home directory looks like this: `databasename1 username1 password1 databasename2 username2 password2` [download] ect.	[reply] [d/l]
Re^2: backtick operator by spjcr (Initiate) on May 13, 2010 at 17:13 UTC
I should clarify - "When I execute the script from the command line I am seeing the correct output." - I am talking about executing the getDBlogin script here	[reply]
Re: backtick operator by AndyZaft (Hermit) on May 13, 2010 at 21:00 UTC
Any reason you have to use that very awkward ksh script to retrieve 2 text fields from a file? While at first look it should run as you expect it, that construct could be avoided, and by doing it from perl you wouldn't have to rely on result from a backtick operation, that could cause various unforeseen issues due to ENV values and many other problems. I'm thinking here something along the lines of: `open(DBFILE,"~/.passwd"); while($line = <DBFILE>) { if ($line =~ /$dbname(\w+)(\w+)/) { $dbUser = $1; $dbPass = $2; } }` [download] If you must have an outside script because it is used from other processes also, you could tidy that one up too with awk for example. The whole writing a temp file to extract a text field is very un-unix way of doing it. `awk '/^abc01/{ print $2 " " $3; }' ~/.passwd` [download] would give you the same fields as the getDBlogin script. The strange part about your log is that the log won't even show what came back from your backtick operation, at least you should see `tempStr:` [download] by itself.	[reply] [d/l] [select]
Re^2: backtick operator by Anonymous Monk on May 13, 2010 at 21:32 UTC
Yeah, I thought about that and completely agree with you - I was just reusing that ksh script someone else had written - I replaced that with: sub dbConnect(){ my ($dbName) = @_; LogStatus "Retrieving $dbName login info"; my ($dbUser, $dbPass) = get_db_login($dbName); LogStatus "User for $dbName is $dbUser"; die "$0: Could not find password for $dbUser" unless(defined($dbPas +s)); my $dbh = DBI->connect("dbi:DB2:$dbName", $dbUser, $dbPass, {AutoCo +mmit=> 0, RaiseError => 1}) \|\| die "Can't connect to $database: $DBI::errstr"; LogStatus "Connected to $dbName as $dbUser"; return $dbh; } sub get_db_login { my ($dbName) = @_; my ($dbUser, $dbPass, $whoami); chomp($whoami = `whoami`); open(PASSWD,"/home/$whoami/.passwd") or die "~/.passwd does not ex +ist"; while(<PASSWD>){ if($_=~/^$dbName\s+(\w+)\s+(\w+)/i){ $dbUser = $1; $dbPass = $2; } } close PASSWD; return $dbUser, $dbPass; } [download] Unfortunately, I am still getting the same behavior as I never see the result of: `LogStatus "User for $dbName is $dbUser";`	[reply] [d/l] [select]
Re^3: backtick operator by AndyZaft (Hermit) on May 13, 2010 at 22:03 UTC
Hmm, but it doesn't die when opening the .passwd file? That's weird, time to debug that get_db_login sub line by line right after the open statement. If for some reason you don't get anything from the file then your while loop would never get executed. Btw, you can use $ENV{USER} instead of `whoami`, one less system call :) I assume it is not dying from `die "$0: Could not find password for $dbUser" unless(defined($dbPass)) +;` [download] since the $dbPass will be defined as an empty string at that point, right?	[reply] [d/l]
Re^4: backtick operator by Anonymous Monk on May 14, 2010 at 03:11 UTC
Re^5: backtick operator by Anonymous Monk on May 14, 2010 at 06:41 UTC
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