shell loop through file lines and replace each line

Question

I am really new to shell scripting, but here is the situation: I have a text file that contains the following :

int1, operationName1
int2, operationName2
int3, operationName3

In a nutshell, the file contains some operations (operationNameX) and the number of days remaining to execute each operation (intX).

I want to write a script that will be executed once per day and removes 1 from each int. for example if "test.txt" contains:

2, operation1
4, operation2
3, operation3

after the execution of the script, it will contain:

1, operation1
3, operation2
2, operation3

any idea on what should I do??

David Hoelzer · Accepted Answer · 2015-05-25 13:53:37Z

1

You could try Awk. It's incredibly powerful and perfect for this kind of thing:

awk -F, '//{VAL=$1; print (VAL-1)", "$2}' test.txt

This sets the field separator to a comma (whitespace, by default), assigns the first element (the integer) to a variable named VAL and then prints out VAL-1 followed by a comma, a space and the original second column.

answered May 25, 2015 at 13:53

David Hoelzer

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2 Comments

Mahmoud Ksemtini Over a year ago

thank you, but can I overwrite the file content by the output of awk??

David Hoelzer Over a year ago

You could but it's generally a bad idea to overwrite your source file atomically. You could cat test.txt | awk ... > test.txt. I'd recommend doing it in two steps, though.

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