Using UNIX commands inside Perl scripts, with Perl variables

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

I need to send a command to UNIX that copies a log file and renames it with a variable in my Perl program. I know how to send commands to UNIX:

print `cp x.txt y.txt';
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which works fine...but if I have the variable a to rename the file with:

print `cp x.txt $a_log.txt`
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the error message comes up when I run the Perl script dbi:

Name "main::a_log" used only once: possible typo at dbi line 146.
Use of uninitialized value in concatenation (.) or string at dbi line 
+146.
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Any suggestions for using perl variables to rename a file with UNIX commands? I've also looked into the system() and exec() commands but have not come up with anything that works.

Comment on Using UNIX commands inside Perl scripts, with Perl variables Select or Download Code

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Re: Using UNIX commands inside Perl scripts, with Perl variables by arturo (Vicar) on Jun 08, 2001 at 01:07 UTC
Your backticks are just fine. The problem is that you're running with warnings turned on and you haven't defined the variable `$a_log` anywhere. When you get error messages you don't understand, a good place to read up on them is `perldoc perldiag`, or better yet, run your script with `use diagnostics;` near the top. Oh yes, and read up on scoping (see Dominus' home node for a great link), and add `use strict;` and declare your variables using `my`, `our` (Perl 5.6.0+) or `use vars qw($var $names)`. You'll thank yourself for it later. Update oh duh. The other replies figured out that you're trying to use `$a` as the variable and append "_log.txt" to the end of it. You could very well be running under `use strict` because `$a` is a special global variable. I'd suggest using something more descriptive anyway, but note that `$a` and `$b` have a special meaning in Perl. Ref: perlfunc:sort `perl -e 'print "How sweet does a rose smell? "; chomp ($n = <STDIN>); +$rose = "smells sweet to degree $n"; other_name = rose; print "$oth +er_name\n"'` [download]	[reply] [d/l] [select]
Re: Using UNIX commands inside Perl scripts, with Perl variables by wog (Curate) on Jun 08, 2001 at 01:07 UTC
First, see the File::Copy module. As for your actual problem, perl is reading `$a_log`, as a variable, instead of just using `$a`. You can fix the problem be explictly saying that "_log" isn't part of the variable by using `${a}` instead of `$a`. You appear to not being using strict. It's a very good idea to do so.	[reply] [d/l] [select]
Re: Using UNIX commands inside Perl scripts, with Perl variables by runrig (Abbot) on Jun 08, 2001 at 01:06 UTC
use "${a}" to keep longer names from being interpolated inside quotes and backticks.	[reply]
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