wildcard : Java Glossary

by Roedy Green ©1996-2009 Canadian Mind Products
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wildcard

In Windows BAT language you can refer to all files in a directory as *.html or all files a?.html for all two-letter files starting with a. The way you specify such a group of files is called a wildcard. * matches any string. ? matches any single character.

Windows

Using cmd.exe as the command processor, or Take Command 4nt.exe, wildcards behave in a way that may surprise you.

cert*.html ⇒ a list of the files matching the pattern. Your Java progam does not need to expand the wild card itself. It does not see the wildcard; it sees only a list of files that match the pattern at its main ( String[] args ) This happens for Java only, it does not happen for C/C++ or assembler utilities.
silly*.html ⇒ silly*.html since there were no matches.
"cert*.html" ⇒ cert*.html, with the quotes stripped off, even though there were matches, suppresses wildcard expansion.
"cert *.html" ⇒ cert *.html, with the quotes stripped off, even though there were matches, suppresses wildcard expansion.

IntelliJ Idea under Windows

Using the IntelliJ Idea IDE to run programs, wildcards behave in a way that may surprise you.

cert*.html ⇒ a list of the files matching the pattern.
silly*.html ⇒ silly*.html since there were no matches.
"cert*.html" ⇒ a list of the files matching the pattern. I think this is a bug.
I tried to fix the problem by quoting the * with "cert\*.html". It treated the \ literally, decided there were matches and returned cert\*.html, with the quotes stripped off, not that useful.
"cert *.html" ⇒ cert *.html, with the quotes stripped off, even though there were matches, suppresses wildcard expansion.

Bash under Linux

Using bash as the script processor, wildcards behave in a way that may surprise you.

cert*.html ⇒ a list of the files matching the pattern.
silly*.html ⇒ silly*.html since there were no matches.
'cert*.html' ⇒ cert*.html, with the apostrophes stripped off, even though there were matches.

I am also told in Linux/bash you can subvert the globbing with \ quoting, e.g. \*.html Then your program will get the command-line parameters unexpanded. See parameter expansion in bash for more details.

Experiment!

It is probably easier to understand this by experiment than by explanation. Here is a simple tool to help you.

Converting Wildcards to Regexes

You can convert a wild card to a regex, then do you own filtering.

Summary

This wildcard expansion mechanism is Mikey Mouse. It does not work for wildcards containing spaces. It is confusing for wildcards without matches. It makes it difficult to pass * or ? as data. I think the best way out is for Sun to provide an alternate mechanism to passing the entire command line completely unmodified.

Parameter expansion in bash
regex
Wildcard Student Project

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