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What Really Happens?

Good question. Actually, there are a couple of special characters intercepted by the shell, bash . The character ``*'', an asterix, says ``replace this word with all the files that will fit this specification''. So, the command cp data* ~/backup, like the one above, gets changed to cp data-new data1 data2 data5 ~/backup before it gets run.

To illustrate this, let me introduce a new command, echo . echo is an extremely simple command; it echoes back, or prints out, any parameters. Thus:


As you can see, the shell expands the wildcard and passes all of the files to the program you tell it to run. This raises an interesting question: what happens if there are no files that meet the wildcard specification? Try echo /rc/fr*og and see what happens...bash  will pass the wildcard specification verbatim to the program.

One word about that, though. Other shells, like tcsh , will, instead of just passing the wildcard verbatim, will reply No match.


The last question you might want to know is what if I wanted to have data* echoed back at me, instead of the list of file names? Well, under both bash and tcsh, just include the string in quotes:




Converted on:
Mon Apr 1 08:59:56 EST 1996