How to get a number with variable number of digits from a string in a file using bash script? - bash

Question

I have the following file:
APP_VERSION.ts
export const APP_VERSION = 1;
This is the only content of that file, and the APP_VERSION variable will be incremented as needed.
So, the APP_VERSION could be a single digit number or multiple digit number, like 15 or 999, etc.
I need to use that value in one of my bash scripts.
use-app-version.sh
APP_VERSION=`cat src/constants/APP_VERSION.ts`
echo $APP_VERSION
I know I can read it with cat. But how can I parse that string so I can get exactly the APP_VERSION value, whether it's 1 or 999, for example.

Answer 1

sed -En 's/(^.*APP_VERSION.*)([[:digit:]]+.*)(\;.*$)/\2/p' src/constants/APP_VERSION
Using sed, split the line into three sections defined by opening and closing brackets. Substitute the line for second section on ( the version value) and print.

Answer 2

You may use this awk:
app_ver=$(awk -F '[[:blank:];=]+' '$(NF-2) == "APP_VERSION" {print $(NF-1)}' src/constants/APP_VERSION.ts)
echo "$app_ver"
1

Answer 3

You can concat some commands to remove everything else:
APP_VERSION=`cat src/constants/APP_VERSION.ts | awk -F '=' '{print $2}' | tr -d ' ' | tr -d ';'`
1 - Cat get all file content
2 - AWK gets all content after '='
3 - Remove space
4 - Remove ;

Answer 4

A simple
APP_VERSION=$(grep --text -Eo '[0-9]+' src/constants/APP_VERSION.ts)
should be enough

Answer 5

With bash only:
APP_VERSION=$(cat src/constants/APP_VERSION.ts)
APP_VERSION=${APP_VERSION%;}
APP_VERSION=${APP_VERSION/*= }
Line 2 removes the trailing ';', line 3 removes everything before "= ".
Alternatively, you could set APP_VERSION as an array, take 5th element, and remove trailing ';'.
Or, another solution, using IFS:
IFS='=;' read a APP_VERSION < src/constants/APP_VERSION.ts
In this version, the space will remain before version number.

Answer 6

Assuming that the task can be rephrased to "extract the digits from a file", there are a few options:
Delete all characters that aren't digits with tr:
version=$(tr -cd '[:digit:]' < infile)
Use grep to match all digits and retain nothing but the match:
version=$(grep -Eo '[[:digit:]]+' infile)
Read file into string and delete all non-digits with just Bash:
contents=$(< infile)
version=${contents//[![:digit:]]}