Perl script runs in terminal but doesn't run when invoked from Java program

Question

I was running a Perl script that replaces a string with another:

perl -pi.back -e 's/str1/str2/g;' path/to/file1.txt

When I run this command from terminal it well replaces all the occurrences of str1 in the given file to str2. When I run this from java it does access the file but no replacement occurs:

Runtime.getRuntime().exec("perl -pi.back -e 's/str1/str2/g;' path/to/file1.txt");

I'm sure it accesses the file (the file seems to be edited in gedit(reload required)).
I tried Java ProcessBuilder class but the same result happens.
When I use Runtime.exec() or ProcessBuilder with other commands (like gedit newFile.txt) they work well.
Ironically, I printed the above perl command from java and take the paste in terminal and the replace operation is done!
No exceptions or errors by using those commands. (I used try and catch to ensure this).
I also used /usr/bin/perl instead of perl in the cmd to ensure the perl cmd is executed.

So what do you think the problem is?

EDIT:

I solved this problem by just removing the quotes from the command in java. Thanks to @ikegami for help. So the working version is:

perl -pi.back -e s/str1/str2/g; path/to/file1.txt

instead of

perl -pi.back -e 's/str1/str2/g;' path/to/file1.txt

exec() returns you a Process, it has getInputStream() and getErrorStream() methods which return you whatever output the process creates. See what this process outputs. — Denis Tulskiy
– Denis Tulskiy, Commented Dec 24, 2012 at 13:53
Depending on the OS, your Java program probably does not have the path to Perl. You'll need to put the full path in to the Perl binary. That's not the only way to do it, but one of the simplest ways. — octopusgrabbus
– octopusgrabbus, Commented Dec 24, 2012 at 14:02
@ikegami I owe you one. Removing the quotes get it working! Thanks but I wanna ask why should I remove the quotes? — a90
– a90, Commented Dec 24, 2012 at 14:16

ikegami · Accepted Answer · 2012-12-24 14:27:23Z

5

exec uses StringTokenizer to parse the command, which apparently just splits on whitespace.

Take for example the following shell command (similar but different than yours):

perl -pi.back -e 's/a/b/g; s/c/d/g;' path/to/file1.txt

For it, StringTokenizer produces the following command and arguments:

perl (command)
-pi.back
-e
's/a/b/g;
s/c/d/g;'
path/to/file1.txt

That's completely wrong. The command and arguments should be

perl (command)
-pi.back
-e
s/a/b/g; s/c/d/g; (Note the lack of quotes.)
path/to/file1.txt

You could pass those above to exec(String[] cmdarray). Or if you don't have the option of parsing the command, you could actually invoke a shell to parse it for you by passing the following to exec(String[] cmdarray):

sh (command)
-c
perl -pi.back -e 's/a/b/g; s/c/d/g;' path/to/file1.txt

answered Dec 24, 2012 at 14:27

ikegami

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1 Comment

ikegami Over a year ago

You should try perl -le'print for @ARGV' perl -pi.back -e 's/str1/str2/g;' path/to/file1.txt and see what is actually passed to Perl by the shell. You should also try it without the (unnecessary) space after the -e.

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