[gllug] echo

[Richard Cohen]

On 4/20/05, Steve Nelson <sanelson at gmail.com> wrote:
> Hi all,
> 
> Just a quickie - I've just discovered (don't laugh!) that 'echo'
> behaves as follows:
> 
> $ echo beer
> beer
> $ echo beer*
> beer*
> $ echo file
> file
> $ echo file*
> file1 file2 file_for_testing
> 
> ie if there is a file matching that which I ask the shell to echo, it
> tells me those files, rather than echoing file*.
> 
> I appreciate that this has to do with shell expansion, such that I can do:
> 
> $ echo 'file*'
> file*
> 
> My question is why this is connected with filenames.  Why does the
> shell look for matching filenames?  ie - Why does echolists all files
> beginning with file.  The echo(1)  manual page doesn't help.

The point is that what you type isn't what gets sent to echo.  The
shell performs expansion *before* passing the command-line onto the
command, so when you type "echo beer*" the beer* doesn't match
anything, so echo sees "beer*" as the argument list.  When you type
"echo file*", the shell expands the file* and passes "file1 file2
file_for_testing" onto echo as its command-line argument list.

It's trivial to test this with a tiny program in any language which
lets you access the command-line args:
-----
#! /usr/bin/python

import sys

for i in range(len(sys.argv)):
    print "arg number %d is %s" % (i, sys.argv[i])
-----

> I'm sure this is blindingly obvious, but I'm curious!
> 
> S.

Cheers
Richard
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