Why doesn't my Perl one-liner work on Windows?

Question

From the Windows command prompt I generate a text file of all the files in a directory:

dir c:\logfiles /B > config.txt

Output:

0001_832ec657.log
0002_a7c8eafc.log

I need to feed the "config.txt" file to another executable, but before I do so, I need to modify the file to add some additional information that the executable needs. So I use the following command:

perl -p -i.bak -e 's/log/log,XYZ/g' config.txt

I'm expecting the result to be:

0001_832ec657.log,XYZ
0002_a7c8eafc.log,XYZ

However, the "config.txt" file is not modified. Using the "-w" option, I get the warning message:

Useless use of a constant in void context at -e line 1.

What am I doing wrong?

Answer 1

Windows cmd.exe does not use ' as string delimiters, only ". What you're doing is equivalent to:

perl -p -i.bak -e "'s/log/log,XYZ/g'" config.txt

so -w is complaining "you gave me a string but it does nothing".

The solution is to use double quotes instead:

perl -p -i.bak -e "s/log/log,XYZ/g" config.txt

or to simply leave them off, since there's no metacharacters in this command that would be interpreted by cmd.exe.

Addendum

cmd.exe is just a really troublesome beast, for anybody accustomed to sh-like shells. Here's a few other common failures and workarounds regarding perl invocation.

@REM doesn't work:
perl -e"print"
@REM works:
perl -e "print"
@REM doesn't work:
perl -e "print \"Hello, world!\n\""
@REM works:
perl -e "print qq(Hello, world!\n)"

Answer 2

ephemient's answer summarizes the problem well, but you do have another option: change your shell from cmd.exe to a better shell. If you are a Unix type person then I would suggest looking into Cygwin which provides the sort of environment you are used to (for example, Bash and GNU utilities).

If you are a Windows-type person I would suggest looking at PowerShell (née MSH née Monad). In fact, I would suggest looking into PowerShell even if you are Unix type person. It integrates with .NET and has many neat features (like objects being passed through pipes rather than simple lines of text). If I were stuck on a Microsoft OS, it is the shell I would be using.

Other shells for Windows that people seem to like:

• UWIN
• MinGW
• UnixUtils
• Microsoft Windows Services for UNIX (SFU)
• MKS Toolkit