bash script to convert values before an equal sign to lowercase? - bash

Question

I'm trying to achieve the following results:
I have a command that spits out some env vars to the terminal:
./script will output the following:
AWS_OKTA_PROFILE=xxx
AWS_ACCESS_KEY_ID=xxx
AWS_SECRET_ACCESS_KEY=xx
AWS_SECURITY_TOKEN=xx
AWS_SESSION_TOKEN=xx
I want to write this to an output file in another location to be almost the same except like this (but only before the equal sign)
[default]
aws_okta_profile=xxx
aws_access_key_id=xxx
aws_secret_access_key=xx
aws_security_token=xx
aws_session_token=xx
Notice, I'm also prepending [default] to the file.
Thanks!

Answer 1

In addition to sed, awk also provides a simple solution. You can use the '=' as the field-separator and simply convert the first field to lowercase with tolower() if the record contains an '=' sign. (or you can check NF>1 to check you have more than one field) The 1 at the end of the rule is simply short-hand for print. Putting it altogether, you can use
awk -F= -v OFS='=' '/=/{$1=tolower($1)}1' file
Example Use/Output
With your input in the file file, you would get:
$ awk -F= -v OFS='=' '/=/{$1=tolower($1)}1' file
[default]
aws_okta_profile=xxx
aws_access_key_id=xxx
aws_secret_access_key=xx
aws_security_token=xx
aws_session_token=xx
awk does not have an edit in-place mechanism (except by non-standard extension), so simply redirect the output to a new file, e.g.
$ awk -F= -v OFS='=' '/=/{$1=tolower($1)}1' file > newfile

Answer 2

The search and replace with lowercase can be done with sed like this:
#!/usr/bin/env -S sed -f
s/\([^=]\+\)=\([^=]\+\)/\L\1=\E\2/
s/\([^=]\+\)=\([^=]\+\)/: search regex pattern:
\([^=]\+\): capture group of 1 or more characters not an = sign,
=: followed by an = sign,
\([^=]\+\): followed by another captured group of 1 or more characters not an = sign.
/\L\1=\E\2/: Replace matches with this:
\L\1: Lowercase the captured group 1,
=: followed by an = sign,
\E\2: followed by captured group 2 with case unchanged.