script for restore missing file

[Alexandre34]

Hi everybody.
I am not very skilled with shell scripts, so I prefer to ask: I want to copy the file /boot/config.old to /boot/config.txt IF /boot/config.txt is missing OR has a size=0
I can make it with a c program, but I would prefer make a shell script or use commands in the /etc/rc.local script.
Do you have a example of testing if file exists or size=0 in a script ?

[topguy]

Since we assume its a text file you can use "wc" to count text lines. A count of zero means empty file or at least not a proper config.txt

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wc -l  < /boot/config.txt

or you can count bytes.

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wc -c  < /boot/config.txt

[B.Goode]

The default shell for the pi user under Raspbian is bash.

So you need to refer to the documentation for bash

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man bash

Scroll a long way down to Conditional Expressions.

You will find
-a file
True if file exists

and
-s file
True if file exists and has a size greater than zero.