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Full Discussion: Difference between echo `ls -l` and echo "`ls -l`" ?
Top Forums UNIX for Dummies Questions & Answers Difference between echo `ls -l` and echo "`ls -l`" ? Post 302912076 by sreyan32 on Tuesday 5th of August 2014 02:48:34 PM
Old 08-05-2014
Difference between echo `ls -l` and echo "`ls -l`" ?
Hi guys,
Been messing around with shell programming for a couple of days and I found something that was pretty odd in the behavior of the echo command. Below is an example-:

When I type the following in my /home directory from my lxterminal in Debian-:

echo "`ls -l`"

I get the following output-:
Code:
sreyan@debian:~$ echo "`ls -l`"
total 2296148
drwx------ 4 sreyan sreyan       4096 Jul 31 15:21 Desktop
-rw------- 1 sreyan sreyan     102097 Dec 26  2009 Euphoria.jpg
drwx------ 3 sreyan sreyan       4096 Feb 10 21:28 GNUstep
-rw------- 1 sreyan sreyan 1239269270 Aug 21  2009 linux.x64_11gR2_database_1of2.zip
-rw------- 1 sreyan sreyan 1111416131 Aug 21  2009 linux.x64_11gR2_database_2of2.zip
-rw-r--r-- 1 sreyan sreyan     447144 Jul 24 18:34 RedshiftGUI-0.2.1-Linux-x86_64.deb

Now this is what I expected. I know whatever is put in ` ` is suppose to interpreted as a command in the BASH echo. So, therefore this is the expected output of ls -l on my /home directory.

But it gets weird when I remove the " " (double quotes) from the echo statement.

When I run the following-:

echo `ls -l`

I get as output the following-:
Code:
total 2296148 drwx------ 4 sreyan sreyan 4096 Jul 31 15:21 Desktop -rw------- 1 sreyan sreyan 102097 Dec 26 2009 Euphoria.jpg drwx------ 3 sreyan sreyan 4096 Feb 10 21:28 GNUstep -rw------- 1 sreyan sreyan 1239269270 Aug 21 2009 linux.x64_11gR2_database_1of2.zip -rw------- 1 sreyan sreyan 1111416131 Aug 21 2009 linux.x64_11gR2_database_2of2.zip -rw-r--r-- 1 sreyan sreyan 447144 Jul 24 18:34 RedshiftGUI-0.2.1-Linux-x86_64.deb

If you look closely you will see that it is exactly identical to the output that is given above except for the fact that it contains no line breaks. My question is why ?

  1. Why are the line-breaks removed when I remove the double quotes from echo ? Whatever is there in ` `(tild signs) is supposed to be interpreted as a command right ?
  2. If removal of double quotes " " means that there is a change in the meaning of the echo, then please tell me what is the special meaning that double quotes has in echo ?
  3. Is there any difference between echo "$SHELL" and echo $SHELL ? I know the output is same but since one has double quotes and one doesn't is there any difference in the way that BASH treats them internally ?
I am using Debian Wheezy LXDE with Bash 4.2.
Thanks.
 

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LEARN ABOUT SUSE

echo

ECHO(1) 							   User Commands							   ECHO(1)

NAME

       echo - display a line of text

SYNOPSIS

       echo [SHORT-OPTION]... [STRING]...
       echo LONG-OPTION

DESCRIPTION

       Echo the STRING(s) to standard output.

       -n     do not output the trailing newline

       -e     enable interpretation of backslash escapes

       -E     disable interpretation of backslash escapes (default)

       --help display this help and exit

       --version
	      output version information and exit

       If -e is in effect, the following sequences are recognized:

       NNN  the character whose ASCII code is NNN (octal)

       \     backslash

       a     alert (BEL)

            backspace

       c     produce no further output

       f     form feed

       
     new line

       
     carriage return

       	     horizontal tab

       v     vertical tab

       NOTE: your shell may have its own version of echo, which usually supersedes the version described here.	Please refer to your shell's docu-
       mentation for details about the options it supports.

AUTHOR

       Written by Brian Fox and Chet Ramey.

REPORTING BUGS

       Report echo bugs to bug-coreutils@gnu.org
       GNU coreutils home page: <http://www.gnu.org/software/coreutils/>
       General help using GNU software: <http://www.gnu.org/gethelp/>

COPYRIGHT

       Copyright (C) 2009 Free Software Foundation, Inc.  License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>.
       This is free software: you are free to change and redistribute it.  There is NO WARRANTY, to the extent permitted by law.

SEE ALSO

       The full documentation for echo is maintained as a Texinfo manual.  If the info and echo programs are properly installed at your site,  the
       command

	      info coreutils 'echo invocation'

       should give you access to the complete manual.

GNU coreutils 7.1						     July 2010								   ECHO(1)
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