In several scripts that process files matched by name pattern I needed to add a check for file existence. Just to illustrate let's say I need to process all N??? files:
If there is no N files, this for loop would try to execute ls with non-existent pattern:
To avoid running a process against non-existent file I add if file exists check:
Is there any way in shell to not use those file exists checks and still run process only for an exisant file?
Could you please try following and let me know this helps you.
Above will not print anything errors on standard output. Although you could simply use following too.
But only thing above will print value N??? even it is not present but no error will be printed on standard output, so in case you don't want to print filename then you could directly use as follows.
I hope this helps you.
I added the echo in the loop to show that when nothing matches the N??? pattern the fn variable assumes value of N??? and that is the root of the question - when using
construct I thought the pattern evaluation happens before do and shell would simply not enter the do loop part when nothing matches.
I added the echo in the loop to show that when nothing matches the N??? pattern the fn variable assumes value of N??? and that is the root of the question - when using
construct I thought the pattern evaluation happens before do and shell would simply not enter the do loop part when nothing matches.
Some, shells have an option (as an extension to the standards) that does remove globbing patterns that do not match any existing files. For instance, if you are using a recent bash, the code:
would not run the loop at all if N??? does not match any files in the current working directory, while the other options work with any shell based on Bourne shell syntax:
which works fine as long as you know that there will never be a file actually named N???. (Note that the break could be replaced by a continue and get the same results.) Or, you can use:
(Note that you need to use continue in this form (not break) to protect yourself in case a file is removed while the loop is running (you just want to skip processing the file that was removed; not skip processing other remaining files with names that sort after the file that was removed).
These 2 Users Gave Thanks to Don Cragun For This Post:
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