diff $Var1 $Var2 ?

Xeratul · 01-12-2012, 01:19 AM

Hi, I am looking for a solution for comparing two variables without using a tmp file (written on hdd), and only work with variables. Target: I simply would like to output the new lines that have been seen into $Var2.

sthg like this for instance.

Code:

diff -someoptions $Var1 $Var2

Until now, I use this method (that I do not favor), because ram can do it as well

Code:

comm --nocheck-order  -3  $file1 $file2

with file1=`cat $Var1` and file2=`cat $Var2`

Maybe you have a trick ...

fukawi1 · 01-12-2012, 01:30 AM

Depending on whats in the variables you could do it with a simple if statement.

Code:

~/tmp $ echo $var1 $var2 $var3
abc abc zxc
~/tmp $ if [ $var1 != $var2 ]; then echo "$var1 : $var2"; fi
~/tmp $ if [ $var1 != $var3 ]; then echo "$var1 : $var3"; fi
abc : zxc
~/tmp $

Dark_Helmet · 01-12-2012, 01:40 AM

Code:

#!/bin/bash

Var1=$( /bin/cat << EOF
Some text
more text
Even more text
EOF
)

Var2=$( /bin/cat << EOF
Some text
more text
New text here
Even more text
And even more new text
EOF
)

/usr/bin/mkfifo fifo1 fifo2

echo "${Var1}" > fifo1 &
echo "${Var2}" > fifo2 &

/usr/bin/diff fifo1 fifo2

/bin/rm fifo1 fifo2

From man 7 fifo:

Code:

A FIFO special file (a  named pipe) is similar to a pipe, except that it is accessed as part of the
file system.  It can be opened by multiple processes for reading or writing.  When processes are
exchanging data via the FIFO, the kernel passes all data internally without writing it to the file
system. Thus, the FIFO special file has no contents on the file system; the file system entry
merely serves as a reference point so  that  processes can access the pipe using a name in the
file system.

EDIT:
I initially thought of the if-statement approach too fukawi1, but it sounds like the OP wants to see the new lines of Var2--not to just visually compare their values.

rknichols · 01-12-2012, 02:19 PM

Instead of explicitly creating and removing the FIFOs, you can use process substitution:

Code:

diff <(echo "$Var1") <(echo "$Var2")

Dark_Helmet · 01-12-2012, 03:24 PM

Much more compact. Kudos. I thought there would be something like that, but couldn't remember it.

onebuck · 01-12-2012, 06:40 PM

Moved: This thread is more suitable in <Programming> and has been moved accordingly to help your thread/question get the exposure it deserves.

David the H. · 01-12-2012, 09:56 PM

It's hard to say without some more context, but since you mention "adding new lines", it sounds like you might possibly want to consider using arrays instead.

Xeratul · 01-13-2012, 01:13 PM

thank you for ur coding interests

lets take 1 example:

let var1 contains

Quote:

A.txt
B
C
D
E

let var2 with

Quote:

C
D
E
F
G
H

my dreamt ouput would be after the kinda diff:

Quote:

A.txt
B
F
G
H

if it would be possible eventually....

Reuti · 01-13-2012, 02:49 PM

Code:

$ join -v1 -v2 <(echo "$var1") <(echo "$var2")
A.txt
B
F
G
H

In your initial post you only refer to $var2 to be output, hence leave -v1 out in this case.