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-:
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-:
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.
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Discussion started by: marcink
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LEARN ABOUT SUNOS
echo
echo(1B) SunOS/BSD Compatibility Package Commands echo(1B)NAME
echo - echo arguments to standard output
SYNOPSIS
/usr/ucb/echo [-n] [argument]
DESCRIPTION
echo writes its arguments, separated by BLANKs and terminated by a NEWLINE, to the standard output.
echo is useful for producing diagnostics in command files and for sending known data into a pipe, and for displaying the contents of envi-
ronment variables.
For example, you can use echo to determine how many subdirectories below the root directory (/) is your current directory, as follows:
o echo your current-working-directory's full pathname
o pipe the output through tr to translate the path's embedded slash-characters into space-characters
o pipe that output through wc -w for a count of the names in your path.
example% /usr/bin/echo "echo $PWD | tr '/' ' ' | wc -w"
See tr(1) and wc(1) for their functionality.
The shells csh(1), ksh(1), and sh(1), each have an echo built-in command, which, by default, will have precedence, and will be invoked if
the user calls echo without a full pathname. /usr/ucb/echo and csh's echo() have an -n option, but do not understand back-slashed escape
characters. sh's echo(), ksh's echo(), and /usr/bin/echo, on the other hand, understand the black-slashed escape characters, and ksh's
echo() also understands a as the audible bell character; however, these commands do not have an -n option.
OPTIONS -n Do not add the NEWLINE to the output.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
+-----------------------------+-----------------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+-----------------------------+-----------------------------+
|Availability |SUNWscpu |
+-----------------------------+-----------------------------+
SEE ALSO csh(1), echo(1), ksh(1), sh(1), tr(1), wc(1), attributes(5)NOTES
The -n option is a transition aid for BSD applications, and may not be supported in future releases.
SunOS 5.10 3 Aug 1994 echo(1B)