adding a number to a variable

Question

I am trying to get the contents of a txt file "usernum.txt", get the contents, add one to that number, and replace the current number with the new one. Here is what I have so far

#!/bin/sh ID=0 cat ''$pwd'usernum.txt' >> $ID count1=1 IDB=$(($ID+$count1)) rm "usernum.txt" touch "usernum.txt" echo $IDB >> usernum.txt

It runs but when I open the file, it stays the same. Any ideas? Thanks, Mike

possible duplicate of Creating a counter for a shell script

chepner
– chepner

2012-09-20 12:32:56 +00:00
Commented Sep 20, 2012 at 12:32 — chepner
– chepner, Commented Sep 20, 2012 at 12:32

raam86 · Accepted Answer · 2012-09-20 09:42:53Z

You should store the output from cat into ID instead of using >>. The way you are doing that you always add to a file named '0'. To store the output of cat use:

ID=$( cat 'usernum.txt' )

I have also removed the 'pwd' as you do not need it and also it gets escaped by the single quotes.

EDIT: here is a complete working example. Note that if there is no usernum.txt file this will print some errors(cat and rm fail) but still will work(i.e. will print 1 in the file). You should perform a check to see if the file exists to avoid these errors:

ID=$( cat 'usernum.txt' ) count1=1 IDB=$(($ID+$count1)) rm "usernum.txt" touch "usernum.txt" echo $IDB >> usernum.txt

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