Modifying a variable value

kartikkumar84@g · #1 (**permalink**) 05-14-2008

Hi all, how do i modify a variable's value.

var1='abcd efgh ijkl mnop abcd'

how do i get var2 from var1

var2=$(......)
$echo var2
abcd efgh ijkl mnop

i.e. i have removed a duplicate occurence.

or in general how to modify a varible.

thanks in advance

era · #2 (**permalink**) 05-14-2008

It's not at all clear what concept you are looking for. Perhaps you could elaborate on that a bit. In the meantime, here are some hopefully useful exercises.

Code:

var2=$var1   #copy var1 to var2
var2=${var2%abcd}  # trim abcd from end, if present
var2=`echo "$var2" | tr ' ' '\012' | sort | uniq | tr '\012' ' '` # remove duplicate tokens

The token duplicate removal is probably quite different from what you are imagining it would be, and has the unfortunate side effect of sorting the remaining tokens. In this case it doesn't matter, because they were already sorted, but nevertheless it's not a good general-purpose solution if the order of tokens is significant.

Perhaps you should read a tutorial on shell programming at this point; there's a lot of things you can do with variable substitution (${var%trim} is but a single example).

kartikkumar84@g · #3 (**permalink**) 05-14-2008

hi era

I am used to programming in Matlab and C++ and in these languages you can refer to individual members of a variable (array) and compare their values to all the other members using 2 loops. how can i accomplish that in unix. For example

var2=$(users)

will return the current users but if a user is running two instances of a shell then that username will be returned twice. How can i trim the varible $var2 so that multiple occurrences of usernames are eliminated. i can use a for loop to loop through each member of the varible but then how do i compare it to the rest of the usernames in $var2.

I am referring to tutorials as well but most of them jus explain the general syntax of commands. i guess i am not referring to the right ones, will work on tht.

era · #4 (**permalink**) 05-14-2008

In fact my sort | uniq example was not so far off the mark then.

A variable in Bourne classic is just a piece of text; some shells such as bash and ksh have array variables, too. The common trick would be to modify the text so it is in a suitable form by the time you assign it to a variable.

Code:

var2=$(users | sort | uniq)

shamrock · #5 (**permalink**) 05-14-2008

Code:

var2=$(users | awk '{for(i=1; i<=NF; ++i) if(!a[$i]++) printf("%s ", $i)}')

kartikkumar84@g · #6 (**permalink**) 05-22-2008

Quote:

var2=$(users | awk '{for(i=1; i<=NF; ++i) if(!a[$i]++) printf("%s ", $i)}')

Hi, Thank you, this works, is it possible to it without using sed or awk.

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