Do not escape variable in awk

Question

I got a text file a.txt like that:

start_date:{start_date};end_date:{end_date}

I want to replace {start_date} and {end_date} in shell script.

#!/bin/bash
START_DATE="2021-06-01"
END_DATE="2021-06-02"
awk '{gsub(/{start_date}/, '$START_DATE'); gsub(/{end_date}/, '$END_DATE');print $0 }' a.txt

I want to get something like:

start_date:2021-06-01,end_date:2021-06-02

But acutally I got:

start_date:start_date:2014;end_date:2013

It seems that the variable START_DATE and END_DATE was calcuated in script.It try to wrap variable with double quotes but also failed. How to escaped them in awk?

You are interpolating the shell variables without any quoting whatsoever, so they look to Awk like mathematical expressions instead of strings. Indeed, 2021-6-1 evaluates to 2014. — tripleee, Jun 09 '21 at 09:19
Wow! Just wanted to compliment you @tripleee for an excellent diagnosis of the "math" at play. To the original poster, look into `shellcheck` as a tool to help catch many issues like this. It is an eye-opening experience to learn all the potential errors that can happen when working with bash/shell. — user400575, Oct 06 '21 at 22:26
Thanks. The tool is available at http://shellcheck.net/ though of course you can install it locally as well. — tripleee, Oct 07 '21 at 04:45

score 2 · Accepted Answer · answered Jun 09 '21 at 09:06

You can use

awk -v sd="$START_DATE" -v ed="$END_DATE" '{gsub("{start_date}", sd); gsub("{end_date}", ed)}1' a.txt

where

-v sd="$START_DATE" -v ed="$END_DATE" - passes START_DATE and END_DATE variables to the awk script and initialize sd and ed variables with these values
gsub("{start_date}", sd); gsub("{end_date}", ed) - replace the placeholder text with these values
1 replaces print command that is just shorter and does the same.

Do not escape variable in awk

1 Answers1