I'm using Mac OS X. I'm trying to copying some files with cp command for a build script like this.
cp ./src/*/*.h ./aaa But this command fires an error if there is no .h file in ./src directory. How to make the command don't fire the error? (silent failure) The error makes build result fail, but I just want to copy when only there are some header file.
If you're talking about the error message, you can suppress that by sending it to the bit bucket:
cp ./src/*/*.h ./aaa 2>/dev/null If you want to suppress the exit code and the error message:
cp ./src/*/*.h ./aaa 2>/dev/null || : 
: means in this context. cp (should that be desired). The shell builtin true could be used instead and would be more readable. : – What Is the Purpose of the `:' (colon) GNU Bash Builtin? cp not being in PATH somehow...) You're looking for something along the lines of
if [ -e file ] then cp file /somewhere fi (Unfortunately, the -f option is not the droid you're looking for.)
If you want to match a glob, that won't work; use find instead, e.g.:
find ./src -name \*.h -exec cp {} ./destination \; 
set -e, and the file disappears between the [ and the cp invocations, your script will crash). -e instead of -f and what is the difference. Piping the result to true ensures that the command will always succeed. I have tried this on Linux but not on any Mac OS:
cp ./src/*/*.h ./aaa | true 
| is always run while || is only done in case of an error. And true is usually a binary while the colon : is a builtin and doesn't consume a PID. || true would always work, OTOH. Old question, but might still be relevant for others.
If you don't need to use cp, you could try with rsync.
To copy all files from a source to a destination directory, run:
rsync -avzh --ignore-errors /path/to/source /path/to/destination Rsync comes with most Unix-like systems such as Linux, Mac OS X or FreeBSD.
--ignore-missing-args: rsync -av --ignore-missing-args ./src/*/*.h ./aaa This has the advantage over --ignore-errors that the only errors ignored are those related to source files not existing. With --ignore-errors every error is ignored, which may be dangerous. Also, take into account that this parameter is fairly recent, so it might not be present in old versions of rsync. [ -d /path/to/source ] && rsync -avzh --ignore-errors /path/to/source /path/to/destination You could force the correct error status. With a function:
$ cpalways () { cp $1 $2 2>/dev/null ; return 0 ; } Given the following:
$ ls foo bar baz ls: baz: No such file or directory bar foo Regular copy will return an error. It will return an exit status of 1.
$ cp baz bar ; echo $? cp: baz: No such file or directory 1 If we use the cpalways() function above, any errors will be hidden:
$ cpalways baz bar ; echo $? 0 $ cpalways foo bar ; echo $? 0 $ cpalways baz bar ; echo $? 0 
This works
$(cp ./src/*/*.h ./aaa | true)
