Using counter each time you run bash script

Question

Imagine I have a directory with these files:

file-1.txt  file-2.txt ...

I want to write a condition for my bash and check if file-2.txt exists then write output to file-3.txt

sample bash script file:

while read line;do
    <A command here> #could be anything
    if [ "$?" -eq "0" ]; then
        echo "$line" >> file-$counter.txt  #Pay attention to counter here
    fi
done < $LIST

When bash is finished running and stopped. then I want to run it again. now I want to chech if last file is blah blah then tell the counter to write output to new file.

:) this is example of last file was created from running bash — MLSC, Jul 15 '14 at 05:56
How about having a loop where $counter starts at 0 and it counts up by 1, and terminates as soon as `file-$counter.txt` does not exist? Is there any specific part of that that you are unable to write? — David Grayson, Jul 15 '14 at 05:58
No , First time I run bash the output is file-1.txt . I want when it stops running next time I run the bash and output be file-2.txt. next time file-3.txt and so on... — MLSC, Jul 15 '14 at 06:00
OK, then you could trivially modify my idea above so that `$counter` starts at 1 instead of 0. Do you understand my idea? In pseudocode: `counter = 0; while(file-$counter.txt is a file){ $counter = $counter + 1 }` At the end of the loop, you can use the string `file-$counter.txt` as the next unused file to write to. Now you just have to Google around to figure out how to write that in bash. — David Grayson, Jul 15 '14 at 06:02
Could you post it as an answer to be well checked? thank you — MLSC, Jul 15 '14 at 06:04

paxdiablo · Accepted Answer · 2014-07-15T06:30:04.760

You can get the last number of a file with a series of commands, then add one to get the next:

pax> ll file-*.txt
-rw-r--r-- 1 pax None 0 Jul 15 14:01 file-1.txt
-rw-r--r-- 1 pax None 0 Jul 15 14:01 file-10.txt
-rw-r--r-- 1 pax None 0 Jul 15 14:01 file-11.txt
-rw-r--r-- 1 pax None 0 Jul 15 14:01 file-12.txt
-rw-r--r-- 1 pax None 0 Jul 15 14:01 file-13.txt
-rw-r--r-- 1 pax None 0 Jul 15 14:01 file-14.txt
-rw-r--r-- 1 pax None 0 Jul 15 14:01 file-15.txt
-rw-r--r-- 1 pax None 0 Jul 15 14:01 file-2.txt
-rw-r--r-- 1 pax None 0 Jul 15 14:01 file-3.txt
-rw-r--r-- 1 pax None 0 Jul 15 14:01 file-4.txt
-rw-r--r-- 1 pax None 0 Jul 15 14:01 file-5.txt
-rw-r--r-- 1 pax None 0 Jul 15 14:01 file-6.txt
-rw-r--r-- 1 pax None 0 Jul 15 14:01 file-7.txt
-rw-r--r-- 1 pax None 0 Jul 15 14:01 file-8.txt
-rw-r--r-- 1 pax None 0 Jul 15 14:01 file-9.txt

pax> next=$(expr $(ls -1 file-*.txt |sed 's/file-//;s/.txt$//' |sort -nk1 |tail -1) + 1)

pax> echo $next
16

Then you can just use that to create the next one:

pax> touch file-${next}.txt

pax> ll file-*.txt
-rw-r--r-- 1 pax None 0 Jul 15 14:01 file-1.txt
-rw-r--r-- 1 pax None 0 Jul 15 14:01 file-10.txt
-rw-r--r-- 1 pax None 0 Jul 15 14:01 file-11.txt
-rw-r--r-- 1 pax None 0 Jul 15 14:01 file-12.txt
-rw-r--r-- 1 pax None 0 Jul 15 14:01 file-13.txt
-rw-r--r-- 1 pax None 0 Jul 15 14:01 file-14.txt
-rw-r--r-- 1 pax None 0 Jul 15 14:01 file-15.txt
-rw-r--r-- 1 pax None 0 Jul 15 14:23 file-16.txt  <== here it is
-rw-r--r-- 1 pax None 0 Jul 15 14:01 file-2.txt
-rw-r--r-- 1 pax None 0 Jul 15 14:01 file-3.txt
-rw-r--r-- 1 pax None 0 Jul 15 14:01 file-4.txt
-rw-r--r-- 1 pax None 0 Jul 15 14:01 file-5.txt
-rw-r--r-- 1 pax None 0 Jul 15 14:01 file-6.txt
-rw-r--r-- 1 pax None 0 Jul 15 14:01 file-7.txt
-rw-r--r-- 1 pax None 0 Jul 15 14:01 file-8.txt
-rw-r--r-- 1 pax None 0 Jul 15 14:01 file-9.txt

Breaking that line down command by command:

ls -1 file-*.txt           # get all files one per line.
sed 's/file-//;s/.txt$//'  # get rid of "file-" and '.txt', leaves numbers only.
sort -nk1                  # numerically sort (1..15).
tail -1                    # get last entry only (15).
expr $(... + 1)            # add one (16).
next=$(...)                # assign it to "next" variable.

It's not always a good idea to parse the output of ls since filenames can sometimes contain unusual characters. But, if you can guarantee they'll meet your specifications, this will work fine.

Using counter each time you run bash script

1 Answers1