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Shell Programming and Scripting
Check for file existence using wildcards
Post 302363098 by Azhrei on Monday 19th of October 2009 11:27:44 AM
10-19-2009
Thanks for replying and including the solution you ended up using. 
Btw, that looks like C shell code due to the redirection syntax. You really don't want to use the C shell for any kind of production work; it's too buggy and idiosyncratic. Google for "101 reasons not to use the C shell".
A problem with both my code and yours is the assumption that the current directory is readable and thus ls(1) won't fail due to anything other than a wildcard not being replaced by the shell. In the real world this is a reasonable assumption, but truly defensive shell scripting would check for that with and additional if statement of [ -r . ]
Because both of our routines use ls(1) they pay a performance penalty for the fork() and exec() required to run ls(1). If all built-in commands could be used it would be much faster.
For example, using for i in *.[Ll][Aa][Ss]; do break; done would result in the wildcard being expanded but the loop breaking the very first time through. The value of i will either be a real filename (as the wildcard was expanded) or the string *.[Ll][Aa][Ss] and a simple [ -e "$i" ] will determine that. This solution requires no fork/exec and will be much faster.
But I'm betting that the performance is not a big issue anyway.
Btw, that looks like C shell code due to the redirection syntax. You really don't want to use the C shell for any kind of production work; it's too buggy and idiosyncratic. Google for "101 reasons not to use the C shell".
A problem with both my code and yours is the assumption that the current directory is readable and thus ls(1) won't fail due to anything other than a wildcard not being replaced by the shell. In the real world this is a reasonable assumption, but truly defensive shell scripting would check for that with and additional if statement of [ -r . ]
Because both of our routines use ls(1) they pay a performance penalty for the fork() and exec() required to run ls(1). If all built-in commands could be used it would be much faster.
For example, using for i in *.[Ll][Aa][Ss]; do break; done would result in the wildcard being expanded but the loop breaking the very first time through. The value of i will either be a real filename (as the wildcard was expanded) or the string *.[Ll][Aa][Ss] and a simple [ -e "$i" ] will determine that. This solution requires no fork/exec and will be much faster.
But I'm betting that the performance is not a big issue anyway.
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