Difference between echo `ls -l` and echo "`ls -l`" ? Post: 302912076

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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

08-05-2014

Registered User

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 ?

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 ?
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 ?
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.

sreyan32

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LEARN ABOUT MOJAVE

echo

ECHO(1) 						    BSD General Commands Manual 						   ECHO(1)

NAME

     echo -- write arguments to the standard output

SYNOPSIS

     echo [-n] [string ...]

DESCRIPTION

     The echo utility writes any specified operands, separated by single blank (' ') characters and followed by a newline ('
') character, to the
     standard output.

     The following option is available:

     -n    Do not print the trailing newline character.  This may also be achieved by appending 'c' to the end of the string, as is done by iBCS2
	   compatible systems.	Note that this option as well as the effect of 'c' are implementation-defined in IEEE Std 1003.1-2001
	   (``POSIX.1'') as amended by Cor. 1-2002.  Applications aiming for maximum portability are strongly encouraged to use printf(1) to sup-
	   press the newline character.

     Some shells may provide a builtin echo command which is similar or identical to this utility.  Most notably, the builtin echo in sh(1) does
     not accept the -n option.	Consult the builtin(1) manual page.

EXIT STATUS

     The echo utility exits 0 on success, and >0 if an error occurs.

SEE ALSO

     builtin(1), csh(1), printf(1), sh(1)

STANDARDS

     The echo utility conforms to IEEE Std 1003.1-2001 (``POSIX.1'') as amended by Cor. 1-2002.

BSD
								  April 12, 2003							       BSD

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