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How to compare environment variables

Hi all.

I have the following example:

Code:

PATH=/bin:/usr/bin

new=/tmp/wwho1.$$

old=/tmp/wwho2.$$

>$old

while :

do

  who >$new

  diff $old $new

  mv $new $old

  sleep 60

done

I want to use environment variables instead of 'new' and 'old' files. How to compare environment variables?

Code:

new=$(who)

if [[ $new != $old ]]

then

    do something

fi

old=$new

Your current code diffs the 2 temp files but doesn't care about the results... Why?

diff - compare files line by line

I want to use environment variables instead files. How to do this?

Quote:

Originally Posted by SeRGeiSarov

diff - compare files line by line

I want to use environment variables instead files. How to do this?

With bash/zsh and some other modern shells you could:

Code:

% a="a" b="b";diff <(echo "$a") <(echo "$b") 

1c1

< a

---

> b

Quote:

Originally Posted by radoulov

With bash/zsh and some other modern shells you could:

Code:

% a="a" b="b";diff <(echo "$a") <(echo "$b") 

1c1

< a

---

> b

I don't understand how this script work. Please explain this script.

Quote:

Originally Posted by SeRGeiSarov

I don't understand how this script work. Please explain this script.

Compares variables with diff (as you asked):

Code:

% echo "$var1"

line1

line2

line3

% echo "$var2"

line1

line2

% diff <(echo "$var1") <(echo "$var2") 

3d2

< line3

Is it clear now?

Code:

man diff



Display the differences between two files, or each corresponding file in two directories.

Each set of differences is called a "diff" or "patch". For files that are identical, `diff' normally produces no output; for binary (non-text) files, `diff' normally reports only that they are different.

...

In the simplest case, diff compares the contents of the two files from-file and to-file. A file name of - stands for text read from the standard input.



If from-file is a directory and to-file is not, diff compares the file in from-file whose file name is that of to-file, and vice versa. The non-directory file must not be -.



If both from-file and to-file are directories, diff compares corresponding files in both directories, in alphabetical order; this comparison is not recursive unless the -r or --recursive option is given.



GNU `diff' can show whether files are different without detailing the differences.

It also provides ways to suppress certain kinds of differences that are not important to you.



Most commonly, such differences are changes in the amount of white space between words or lines. `diff' also provides ways to suppress differences in alphabetic case or in lines that match a regular expression that you provide.

I don't see anything about it. Is this feature of BASH?

Quote:

Originally Posted by SeRGeiSarov

[...]
I don't see anything about it. Is this feature of BASH?

The process substitution (<(...)): yes.

Quote:

Originally Posted by radoulov

The process substitution (<(...)): yes.

Thank you :)