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Anonymous Platypus
Asked: 2016-03-25 01:45:48 +0800 CST

Why doesn't cp detect '\ ' (backslash+space)?

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I was trying to write a shell script to copy files. Here is what I have done.

 workingDirectory=$(pwd | sed "s/ /\\ /g")

Now echo $workingDirectory shows /home/user/Documents/Learning and Development/.

But I know, in order for cp command to work I need to replace spaces with \ (backslash+space). So I changed the sed command slightly as,

workingDirectory=$(pwd | sed "s/ /\\\ /g")

So that, echo $workingDirectory shows /home/user/Documents/Learning\ and\ Development/. All good.

But when try to use cp command as,

cp $workingDirectory/jad/jad /usr/bin/

I get errors,

cp: cannot stat ‘/home/user/Documents/Learning\\’: No such file or directory
cp: cannot stat ‘and\\’: No such file or directory
cp: cannot stat ‘Development/jad/jad’: No such file or directory

What could be the reason? How to resolve this?

EDIT

If I use the first sed command, then the errors are 

cp: cannot stat ‘/home/user/Documents/Learning’: No such file or directory
cp: cannot stat ‘and’: No such file or directory
cp: cannot stat ‘Development/jad/jad’: No such file or directory
command-line

1 Answers

  1. Best Answer

    Escaping a field separator inside a variable to prevent word splitting isn't useful: the shell will still split words on the separators listed in $IFS:

    ~/tmp/directory with spaces$ workingDirectory=$(pwd | sed "s/ /\\\ /g")
~/tmp/directory with spaces$ echo $workingDirectory 
/home/user/tmp/directory\ with\ spaces
~/tmp/directory with spaces$ strace /bin/echo $workingDirectory |& grep '^execve'
execve("/bin/echo", ["/bin/echo", "/home/user/tmp/directory\\", "with\\", "spaces"], [/* 62 vars */]) = 0

    So an obvious workaround for that would be setting $IFS to an empty string (and avoiding escaping spaces at all), essentially disabling word splitting entirely:

    ~/tmp/directory with spaces$ workingDirectory=$(pwd)
~/tmp/directory with spaces$ echo $workingDirectory 
/home/user/tmp/directory with spaces
~/tmp/directory with spaces$ IFS=
~/tmp/directory with spaces$ strace -s 64 /bin/echo $workingDirectory |& grep '^execve'
execve("/bin/echo", ["/bin/echo", "/home/user/tmp/directory with spaces"], [/* 62 vars */]) = 0
~/tmp/directory with spaces$ stat $workingDirectory
  File: ‘/home/user/tmp/directory with spaces’
  Size: 4096        Blocks: 8          IO Block: 4096   directory
Device: 812h/2066d  Inode: 782086      Links: 2
Access: (0775/drwxrwxr-x)  Uid: ( 1000/    user)   Gid: ( 1000/    user)
Access: 2016-03-24 11:22:43.606332994 +0100
Modify: 2016-03-24 10:51:00.835689309 +0100
Change: 2016-03-24 10:51:00.835689309 +0100
 Birth: -

    However disabling word splitting entirely in general doesn't make too much sense. Unless you have good reasons to disable word splitting entirely for more than one command I suggest you simply use double quotes to prevent it limitedly to the strings that can possibly contain field separators:

    workingDirectory=$(pwd)
cp "$workingDirectory"/jad/jad /usr/bin/
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