Bash script: how do I read a variable content from file file and increment it +1

Question

I'm writing an basic bash script where I'm reading a file which contains initially "1" as content. After reading it I want to increase it +1 everytime whenever I run the script.

Example file: 1.txt

1

Initial Content: 1

Expected output when run first time: 1.txt

2

Here is my script

#!/misc/acc-archive/util/bash

i=$(<1.txt)

echo "$1"

j=$((i+=1))

echo "$1"

find . -exec perl -pi -e 's/$1/$j/g' 1.txt \;

Answer 1

You made a few mistakes. Here is a working copy:

i=$(cat 1.txt)

echo "i: $i"

j=$((i+=1))

echo "j: $j"
echo "$j" > 1.txt

I changed:

• $1 to $i
• switched from < to cat
• replaced the find/perl combination with just a >

Answer 2

If you're replacing the entire contents of the file:

#!/bin/bash

i=$(<1.txt)
echo "$((++i))" > 1.txt

If you need to edit numbers in place in multiple files, you should provide more specific details about your task.