Help in explaining this echo conundrum. Post: 302993800

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Operating Systems OS X (Apple) Help in explaining this echo conundrum. Post 302993800 by Scrutinizer on Tuesday 14th of March 2017 01:46:59 PM

03-14-2017

Moderator

Note that there is a reason that echo is not part of the POSIX specification. For consistent results, it is best to only use printf

Code:

sh-3.2$ /usr/bin/printf '1\n2\n2\n3\n5\n'
1
2
2
3
5
sh-3.2$ printf '1\n2\n2\n3\n5\n'
1
2
2
3
5

I get

Code:

sh-3.2$ echo '1\n2\n3\n4\n5' | od -bc
0000000   061 012 062 012 063 012 064 012 065 012                        
           1  \n   2  \n   3  \n   4  \n   5  \n                        
0000012
sh-3.2$ /bin/echo '1\n2\n3\n4\n5' | od -bc
0000000   061 134 156 062 134 156 063 134 156 064 134 156 065 012        
           1   \   n   2   \   n   3   \   n   4   \   n   5  \n        
0000016

So in the first case \n is interpreted as newline, in the second case it is not.

--
Interestingly:

When I do:
/bin/bash --posix, which is supposed to be the same as /bin/sh I get:

Code:

bash-3.2$ echo '1\n2\n3\n4\n5' | od -bc
0000000   061 134 156 062 134 156 063 134 156 064 134 156 065 012        
           1   \   n   2   \   n   3   \   n   4   \   n   5  \n        
0000016

Also when bash is invoked without the --posix option

On OSX, apparently it is not a link to /bin/bash as is the case on some Linux distributions, but rather they are two distinct binaries

Code:

sh-3.2$ ls -l /bin/sh /bin/bash
-r-xr-xr-x  1 root  wheel  626272 Sep 14 02:57 /bin/bash
-r-xr-xr-x  1 root  wheel  630464 Sep 14 02:57 /bin/sh

If I make a symlink sh -> /bin/bash

Code:

$ ./sh
sh-3.2$ echo '1\n2\n3\n4\n5' | od -bc
0000000   061 134 156 062 134 156 063 134 156 064 134 156 065 012        
           1   \   n   2   \   n   3   \   n   4   \   n   5  \n        
0000016

Last edited by Scrutinizer; 03-14-2017 at 03:08 PM..

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