How to let 'cp' command don't fire an error when source file does not exist?

Question

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.

score 140 · Accepted Answer · answered Jun 23 '10 at 04:07

140

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 || :

answered Jun 23 '10 at 04:07

Dennis Williamson

62,879

20

It would be nice to explain what : means in this context. – Piotr Dobrogost Feb 10 '14 at 15:35
37

@PiotrDobrogost: In Bash and some other shells the colon is a null utility (no-op). It's specified by POSIX. Since it always returns true, it's used here to suppress the exit code of a failed cp (should that be desired). The shell builtin true could be used instead and would be more readable. – Dennis Williamson Feb 10 '14 at 15:46
1

More about : – [What Is the Purpose of the `:' (colon) GNU Bash Builtin?](http://stackoverflow.com/q/3224878/95735) – Piotr Dobrogost Feb 10 '14 at 15:49
4

This will also ignore other errors (source/destination directory doesn't exist, source file exists but is not readable, disk full, read-only filesystem, IO error, cp not being in PATH somehow...) – Vladimir Panteleev Oct 24 '18 at 19:32
syntax error near unexpected token `||' – thang Jul 24 '19 at 20:53
@thang: What shell are you using? – Dennis Williamson Jul 24 '19 at 21:48
ubuntu's default bash. i guess linux bash is different from mac os bash. – thang Jul 25 '19 at 22:03
@thang: All versions of Bash at least as far back as version 2 (ancient) support || regardless of operating system. What does false || echo "OR" output for you? – Dennis Williamson Jul 25 '19 at 22:10
|| seems to work in shell but doesn't when i put into shell script. i think that's the culprit – thang Jul 26 '19 at 01:39
@thang: How are you running your script? bash ./scriptname for example? Or with a shebang like #!/bin/bash? Or do you have stray characters in your script such as Windows/DOS line endings \r\n? – Dennis Williamson Jul 26 '19 at 02:55
#!/bin/bash everything is linux, so nothing windows. – thang Jul 26 '19 at 03:34
@thang: Well without seeing the actual line there's nothing else I can suggest. – Dennis Williamson Jul 26 '19 at 03:43
thanks for your help. i did a work around with if [-f ...] before doing cp. probably not the most elegant but it works and it's a shell script so elegance isn't so important. – thang Jul 26 '19 at 14:21

Brad Ackerman · Answer 2 · 2010-06-23T03:27:27.793

25

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 \;

edited Jun 23 '10 at 03:27

answered Jun 23 '10 at 03:19

Brad Ackerman

2,221

1

Note that there is a potential TOCTOU issue with such an approach (e.g. if you use set -e, and the file disappears between the [ and the cp invocations, your script will crash). – Vladimir Panteleev Oct 24 '18 at 19:34
You could explain why use -e instead of -f and what is the difference. – Fabiano Arruda Jan 06 '24 at 19:31

score 16 · Answer 3 · edited Feb 06 '15 at 17:56

16

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

edited Feb 06 '15 at 17:56

Andrew Schulman

8,916

answered Feb 06 '15 at 16:41

Vivek

261

12

The simple pipe | 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. – ott-- Feb 06 '15 at 18:16
1

A bash script on MacOS - Yosemite containing "cp ./src//.h ./aaa" command does not error out if the .h files do not exist. – Vivek Feb 21 '15 at 07:29
Simple, readable, and working. This is exactly what I needed, thanks mate. – Kostiantyn Ko Jul 08 '22 at 23:36

score 13 · Answer 4 · answered Aug 22 '15 at 16:22

13

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.

answered Aug 22 '15 at 16:22

mre

311
2
7

5

You could use rsync instead of cp, adding the parameter --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. – jesjimher Oct 15 '15 at 10:18
what if the source directory doesn't exist? – Arrrow Jun 18 '20 at 07:37
1

I don't think that should be the responsibility of rsync to be honest. Rather, you can check upfront if the source directory exists, e.g. [ -d /path/to/source ] && rsync -avzh --ignore-errors /path/to/source /path/to/destination – mre Jun 18 '20 at 11:30

score 2 · Answer 5 · answered Jun 23 '10 at 04:12

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

score -1 · Answer 6 · answered Mar 29 '21 at 17:05

-1

This works

$(cp ./src/*/*.h ./aaa | true)

answered Mar 29 '21 at 17:05

Hemant_Negi

95

How to let 'cp' command don't fire an error when source file does not exist?

6 Answers6