Sponsored Content
Operating Systems OS X (Apple) Help in explaining this echo conundrum. Post 302993798 by wisecracker on Tuesday 14th of March 2017 01:41:35 PM
Old 03-14-2017
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...
 

8 More Discussions You Might Find Interesting

1. 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

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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
tabs(1) 						      General Commands Manual							   tabs(1)

NAME
tabs - set tabs on a terminal SYNOPSIS
[tabspec] n] type] DESCRIPTION
sets the tab stops on the user's terminal according to the tab specification tabspec, after clearing any previous settings. The user's terminal must have remotely-settable hardware tabs. If you are using a non-HP terminal, you should keep in mind that behavior will vary for some tab settings. Four types of tab specification are accepted for tabspec: ``canned'', repetitive, arbitrary, and file. If no is given, the default value is i.e., UNIX ``standard'' tabs. The lowest column number is 1. Note that for tabs, column 1 always refers to the left-most column on a terminal, even one whose column markers begin at 0. Gives the name of one of a set of ``canned'' tabs. Recognized codes and their meanings are as follows: 1,10,16,36,72 Assembler, IBM S/370, first format 1,10,16,40,72 Assembler, IBM S/370, second format 1,8,12,16,20,55 COBOL, normal format 1,6,10,14,49 COBOL compact format (columns 1-6 omitted). Using this code, the first typed character corresponds to card column 7, one space gets you to column 8, and a tab reaches column 12. Files using this tab setup should have specify a format specification file as defined by below. The file should have the following format specification: 1,6,10,14,18,22,26,30,34,38,42,46,50,54,58,62,67 COBOL compact format (columns 1-6 omitted), with more tabs than This is the recommended format for COBOL. The appro- priate format specification is: 1,7,11,15,19,23 FORTRAN 1,5,9,13,17,21,25,29,33,37,41,45,49,53,57,61 PL/I 1,10,55 SNOBOL 1,12,20,44 UNIVAC 1100 Assembler In addition to these ``canned'' formats, three other types exist: A repetitive specification requests tabs at columns 1+n, 1+2xn, etc. Of particular importance is the value this represents the UNIX ``standard'' tab setting, and is the most likely tab setting to be found at a terminal. Another special case is the value implying no tabs at all. The arbitrary format permits the user to type any chosen set of numbers, separated by commas, in ascending order. Up to 40 numbers are allowed. If any number (except the first one) is preceded by a plus sign, it is taken as an increment to be added to the previous value. Thus, the tab lists 1,10,20,30 and 1,10,+10,+10 are considered identical. If the name of a file is given, reads the first line of the file, searching for a format specification. If it finds one there, it sets the tab stops according to it, otherwise it sets them as This type of specification can be used to ensure that a tabbed file is printed with correct tab settings, and is suitable for use with the command (see pr(1)): Any of the following can be used also; if a given option occurs more than once, the last value given takes effect: usually needs to know the type of terminal in order to set tabs and always needs to know the type to set margins. type is a name listed in term(5). If no option is supplied, searches for the value in the environment (see environ(5)). If is not defined in the environment, tries a sequence that will work for many terminals. The margin argument can be used for some terminals. It causes all tabs to be moved over n columns by making column n+1 the left margin. If is given without a value of n, the value assumed is 10. The normal (left-most) margin on most terminals is obtained by The margin for most terminals is reset only when the option is given explicitly. Tab and margin setting is performed via the standard output. EXTERNAL INFLUENCES
Environment Variables determines the interpretation of text within file as single- and/or multi-byte characters. determines the language in which messages are displayed. If or is not specified in the environment or is set to the empty string, the value of is used as a default for each unspecified or empty variable. If is not specified or is set to the empty string, a default of "C" (see lang(5)) is used instead of If any internationalization variable contains an invalid setting, behaves as if all internationalization variables are set to "C". See environ(5). International Code Set Support Single- and multi-byte character code sets are supported. DIAGNOSTICS
Arbitrary tabs are ordered incorrectly. A zero or missing increment found in an arbitrary specification. A ``canned'' code cannot be found. option was used and file cannot be opened. option was used and the specification in that file points to yet another file. Indirection of this form is not permitted. WARNINGS
There is no consistency among different terminals regarding ways of clearing tabs and setting the left margin. It is generally impossible to usefully change the left margin without also setting tabs. clears only 20 tabs (on terminals requiring a long sequence), but is willing to set 64. SEE ALSO
nroff(1), pr(1), tset(1), environ(5), term(5). STANDARDS CONFORMANCE
tabs(1)
All times are GMT -4. The time now is 10:07 AM.
Unix & Linux Forums Content Copyright 1993-2022. All Rights Reserved.
Privacy Policy