Help in explaining this echo conundrum.

Login or Register for Dates, Times and to Reply

 
Thread Tools Search this Thread
# 1  
Help in explaining this echo conundrum.

OSX 10.12.3, default bash terminal.
Consider this code and note it is calling 'sh' inside the code...
Code:
#!/bin/sh
echo '1\n2\n2\n3\n5' > /tmp/text
hexdump -C /tmp/text
/bin/echo '1\n2\n3\n4\n5' > /tmp/text
hexdump -C /tmp/text

Now view the interactive mode below, note the underlying shell is bash:-
Code:
Last login: Tue Mar 14 17:12:45 on ttys001
AMIGA:barrywalker~> # Use sh first...
AMIGA:barrywalker~> sh
AMIGA:barrywalker~> cd Desktop/Code/Shell
AMIGA:barrywalker~/Desktop/Code/Shell> echo '1\n2\n3\n4\n5' > /tmp/text
AMIGA:barrywalker~/Desktop/Code/Shell> hexdump -C /tmp/text
00000000  31 0a 32 0a 33 0a 34 0a  35 0a                    |1.2.3.4.5.|
0000000a
AMIGA:barrywalker~/Desktop/Code/Shell> /bin/echo '1\n2\n3\n4\n5' > /tmp/text
AMIGA:barrywalker~/Desktop/Code/Shell> hexdump -C /tmp/text
00000000  31 5c 6e 32 5c 6e 33 5c  6e 34 5c 6e 35 0a        |1\n2\n3\n4\n5.|
0000000e
AMIGA:barrywalker~/Desktop/Code/Shell> ./echo_test.sh
00000000  31 0a 32 0a 32 0a 33 0a  35 0a                    |1.2.2.3.5.|
0000000a
00000000  31 5c 6e 32 5c 6e 33 5c  6e 34 5c 6e 35 0a        |1\n2\n3\n4\n5.|
0000000e
AMIGA:barrywalker~/Desktop/Code/Shell> # Now exit sh...
AMIGA:barrywalker~/Desktop/Code/Shell> exit
exit
AMIGA:barrywalker~> bash -version
GNU bash, version 3.2.57(1)-release (x86_64-apple-darwin16)
Copyright (C) 2007 Free Software Foundation, Inc.
AMIGA:barrywalker~> cd Desktop/Code/Shell
AMIGA:barrywalker~/Desktop/Code/Shell> echo '1\n2\n3\n4\n5' > /tmp/text
AMIGA:barrywalker~/Desktop/Code/Shell> hexdump -C /tmp/text
00000000  31 5c 6e 32 5c 6e 33 5c  6e 34 5c 6e 35 0a        |1\n2\n3\n4\n5.|
0000000e
AMIGA:barrywalker~/Desktop/Code/Shell> /bin/echo '1\n2\n3\n4\n5' > /tmp/text
AMIGA:barrywalker~/Desktop/Code/Shell> hexdump -C /tmp/text
00000000  31 5c 6e 32 5c 6e 33 5c  6e 34 5c 6e 35 0a        |1\n2\n3\n4\n5.|
0000000e
AMIGA:barrywalker~/Desktop/Code/Shell> ./echo_test.sh
00000000  31 0a 32 0a 32 0a 33 0a  35 0a                    |1.2.2.3.5.|
0000000a
00000000  31 5c 6e 32 5c 6e 33 5c  6e 34 5c 6e 35 0a        |1\n2\n3\n4\n5.|
0000000e
AMIGA:barrywalker~/Desktop/Code/Shell> _

1) Why does the 'bash' interactive mode give a different result to the 'sh' mode as 'sh' is merely a subset of 'bash'?
2) Why does echo in 'sh' translate '\n' to newlines in single quotes?
I thought single quotes were to give a raw string of characters, irrespective?
(Is this an Apple OSX thing?)
The 'sh' version is the same as the 'bash' version but are NOT identical files.

TIA...
# 2  
'echo' is not consistent or portable between different shells. Sometimes you get newlines, sometimes you get \n, sometimes you only get newlines when you ask for them with echo -e, and sometimes you can't get newlines out no matter what you do (i.e. /bin/sh on solaris). Given OSX's nextstep/mach lineage, I'll wild-guess that their /bin/sh is meant to resemble an old Bourne from BSD.

printf is a lot more consistent.
This User Gave Thanks to Corona688 For This Post:
# 3  
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 04:08 PM..
This User Gave Thanks to Scrutinizer For This Post:
# 4  
@ Scrutinizer...

Also interestingly when using 'dash' on OSX 10.12.3 default bash terminal:-
Code:
Last login: Tue Mar 14 18:32:20 on ttys000
AMIGA:amiga~> /usr/local/bin/dash
AMIGA:\u\w> echo '1\n2\n3\n4\n5' > /tmp/text
AMIGA:\u\w> hexdump -C /tmp/text
00000000  31 0a 32 0a 33 0a 34 0a  35 0a                    |1.2.3.4.5.|
0000000a
AMIGA:\u\w> /bin/echo '1\n2\n3\n4\n5' > /tmp/text
AMIGA:\u\w> hexdump -C /tmp/text
00000000  31 5c 6e 32 5c 6e 33 5c  6e 34 5c 6e 35 0a        |1\n2\n3\n4\n5.|
0000000e
AMIGA:\u\w> exit
AMIGA:amiga~> _

Seems consistent with 'sh'.
I am going to have to be careful with this.

---------- Post updated at 07:39 PM ---------- Previous update was at 07:10 PM ----------

Quote:
Originally Posted by Corona688
'echo' is not consistent or portable between different shells. Sometimes you get newlines, sometimes you get \n, sometimes you only get newlines when you ask for them with echo -e, and sometimes you can't get newlines out no matter what you do (i.e. /bin/sh on solaris). Given OSX's nextstep/mach lineage, I'll wild-guess that their /bin/sh is meant to resemble an old Bourne from BSD.

printf is a lot more consistent.
I do know a few ideas but do not know if this would work in the Solaris situation you quoted.
This is longhand using 'dash' and '/bin/echo'...
You will have to take my word for the 'bold' as it does not copy and paste too well... ;o)
Code:
Last login: Tue Mar 14 19:22:37 on ttys000
AMIGA:amiga~> /usr/local/bin/dash
AMIGA:\u\w> nl='
> '
AMIGA:\u\w> esc=`printf "\033"`
AMIGA:\u\w> /bin/echo '1\n2\n3'
1\n2\n3
AMIGA:\u\w> /bin/echo "1\n2\n3"
1\n2\n3
AMIGA:\u\w> /bin/echo '1${nl}2${nl}3'
1${nl}2${nl}3
AMIGA:\u\w> /bin/echo "1${nl}2${nl}3"
1
2
3
AMIGA:\u\w> # Make characters BOLD...
AMIGA:\u\w> /bin/echo "Normal text, $esc[1mbold text..."
Normal text, bold text...
AMIGA:\u\w> exit
AMIGA:amiga~> _

There are ways to bend rules even in dash...

Last edited by wisecracker; 03-14-2017 at 05:43 PM.. Reason: Sorry about the attachment. I did expect a new window.
# 5  
Quote:
Originally Posted by wisecracker
Seems consistent with 'sh'.
I am going to have to be careful with this.
Basically, only use echo if you want to print preformatted / unescaped data: Any extended behavior like processing backslashes isn't portable.

Quote:
I do know a few ideas but do not know if this would work in the Solaris situation you quoted.
I don't see any point fighting it when there's better alternatives though. Your solution is twice as complicated and much less efficient than just using printf once to do both jobs.
printf "\033[1mBold Text\033[0m Normal Text\n"

You're not breaking the rules, though Smilie It's completely fine to store any ASCII character besides NULL in a variable.

Last edited by Corona688; 03-15-2017 at 01:45 PM..
# 6  
Hi Corona688...
Quote:
I don't see any point fighting it when there's better alternatives though. Your solution is twice as complicated and much less efficient than just using printf once to do both jobs.
Perhaps but my non-rooted Android phone does NOT have printf it only has the same as my echo but the terminal I have on it does emulate the escape codes and the shell resembles a cut down version of bash, probably 'bash --posix' as I can only call it as 'sh'. Hence my experiments with 'echo' over a period of time.
# 7  
Quote:
Originally Posted by wisecracker
Hi Corona688...

Perhaps but my non-rooted Android phone does NOT have printf
Then it's not actually a Bourne shell, and your efforts to be portable with it will be in vain.

If it's not rooted, you're using some weird imitation cooked up in Java and likely don't even have a terminal.

Last edited by Corona688; 03-17-2017 at 02:01 PM..
Login or Register for Dates, Times and to Reply

Previous Thread | Next Thread
Thread Tools Search this Thread
Search this Thread:
Advanced Search

Test Your Knowledge in Computers #836
Difficulty: Medium
SOAP is a data serialization specification.
True or False?

8 More Discussions You Might Find Interesting

1. IP Networking

iptables conundrum

Ok, if youre reading this prepare yourself.(debian based os) so im trying to do this routing with ip tables, i need to forward/SNAT traffic from 192.168.111.1 to 10.10.10.250, the 192.x.x.x ips are being shoved into a honeyd like program called inetsim so its offline, 10.10.10.125 is connected... (3 Replies)
Discussion started by: Shocco
3 Replies

2. Shell Programming and Scripting

Help to explaining a command in run dot tcl

Hi, I'm running a rdt (run dot tcl) command, and come accross this line: alias abc 'set ARGS =(\!*); source home123/abc/$ARGS/setup' What does the command exactly do? Please help. (6 Replies)
Discussion started by: mar85
6 Replies

3. Shell Programming and Scripting

sudo scripts conundrum

hello; Got a problem running monitoring scripts using sudo ssh.. Mgmt decided to take away root sudoers access.. so most of the scripts ran as: sudo ssh $BOX ... Now I need to run them as: echo $my_pw | sudo -S -l my_user_id $BOX ... I tried this but not working.. Any wisdom/tricks... (3 Replies)
Discussion started by: delphys
3 Replies

4. Shell Programming and Scripting

Conundrum - Flexible way to strip extension

Hi, First post here. I have something that may prove to be difficult. I have the following files: Example1.0.0.tar.gz Example2.tar Example3.zip Example4.0.0.0.0.0.bzip2 I need to remove the file extensions and store as a variable so they look like this: Example1.0.0 Example2... (3 Replies)
Discussion started by: Spadez
3 Replies

5. UNIX for Dummies Questions & Answers

umask conundrum

Hi All, i was reading up on a umask question on this forum and have a question on this. the umask value on my home PC running on cygwin is 022. when i create a dir it defaults to permission 755, when i create a file it defaults to 644. Now it starts at 777 for dirs and 666 for files and... (1 Reply)
Discussion started by: Irishboy24
1 Replies

6. UNIX for Dummies Questions & Answers

Explaining some lines from files : .login and .cshrc

Hello, can anyone explain me please what do those lines do ? From file .login 1) set history=40 2) setenv MACH `uname -s` 3) source /etc/login 4) source ~/$MACH/.login From file .cshrc 1) if ( ! $?prompt) exit 0 (5 Replies)
Discussion started by: bbqtoss
5 Replies

7. UNIX for Dummies Questions & Answers

Need help explaining how to use a VPN on a UNIX server with a Mac OS

I have gotten a gig to teach someone how to use a VPN client for a UNIX server on a MAC os. The problem is I have never used UNIX, dont mess with VPN's (my dad has a VPN that I have used a couple of times). I'm currently taking a crash course on UNIX but I was wondering if anyone could help me with... (0 Replies)
Discussion started by: psycopuppy
0 Replies

8. UNIX for Dummies Questions & Answers

explaining awk

i am new to awk scripting. i couldn't figure out how this awk script works can anyone explain? #!/bin/awk -f { for( x=1; x<=NF; ++x) { if( x == 3 ) { continue } print x, $x } } thank you and regards (1 Reply)
Discussion started by: phone_book
1 Replies

Featured Tech Videos