variable incrementation in for loop

++nick++ · 10-20-2011, 09:21 AM

All,

I have a file which contains a list of users,

..
peter
paul
gary
...

I am trying to prepend UID , starting from 500 in the below format so I can add them to the server kickstart file that I am building,

..
500

eter
501

aul
502:gary
..

My script is below,

#!/bin/bash

for x in `cat $file`
do
for (( c=500;c<520;c++ ))
do
echo $c:$x
done
done

520 is a result of wc -l $file,

But the above print out 500..520 for all users in the file,

Can someone please point to the mistake I am making here,

Thanks,

colucix · 10-20-2011, 09:39 AM

The paste command can avoids the loop:

Code:

paste -d: <(seq 500 1019) file

I used 1019 since you stated the file contains 520 different names, so that the first one is numbered 500 and the last one 1019. Is this what you're looking for?

Regarding your script, you have two nested loops, hence for every x (user) it prints out 500:x, 501:x, ... 519:x, 520:x. Rather you actually need a single loop and a counter to increment at each passage:

Code:

c=500
for x in $(cat $file)
do
  echo $c:$x
  ((c++))
done

++nick++ · 10-20-2011, 11:16 AM

Amazing colucix ,it is working like a charm now , I was unable to get the counter to work properly earlier,

Thanks Again , Good Night

David the H. · 10-20-2011, 02:03 PM

Please use [code][/code] tags around your code, to preserve formatting and to improve readability. (You have over a hundred posts, so you should be aware of this by now

)

You can turn off smilies when posting too.

Now for some scripting tips:

1) Don't use a for loop when reading from files or commands. Any input with a space in it would break it. Use a while+read loop instead.

http://mywiki.wooledge.org/DontReadLinesWithFor

2) Useless use of cat. Inside a command substitution $(<filename) does just the same job (well, except that any final newline will be removed). And if you use the while loop I mentioned in #1, you can feed it directly (example below).

3) $(..) is highly recommended over `..`. Please don't use backticks, they're hard to read, easy to mistake, and completely unnecessary.

4) Always quote variable expansions, as word-splitting is done after expansion. (This is also why the command substitution in #1 is a problem).

http://mywiki.wooledge.org/Arguments
http://mywiki.wooledge.org/WordSplitting
http://mywiki.wooledge.org/Quotes

With that said, here's a better example of colucix's code:

Code:

c=500

while read x ; do
	echo "$c:$x"
	((c++))
done <"$file"