Assume a multi-line text file file in which some lines start with whitespaces.
$ cat file
foo Baz
baz QUX
QUx Quux
BaZ Qux
BazaaR
Further assume that I wish to convert all those lines that start with a keyword (e.g. "baz") to lowercase letters, irrespective if (a) that keyword is written in lower- or uppercase letters (or any combination thereof) itself, and (b) that keyword is preceeded by whitespaces.
$ cat file | sought_command
foo Baz # not to lowercase (line does not start with keyword)
baz qux # to lowercase
QUx Quux
baz qux # to lowercase
BazaaR # not to lowercase (line does not start with keyword, but merely with a word containing the keyword)
I believe that awk is the tool to do it, but I am uncertain how to implement the case-insensitivity for the keyword matching.
$ cat file | awk '{ if($1 ~ /^ *baz/) print tolower($0); else print $0}'
foo Baz
baz qux
QUx Quux
BaZ Qux # ERROR HERE: was not replaced, b/c keyword not recognized.
BazaaR
EDIT 1:
Adding IGNORECASE=1 appears to resolve the case-insensitivity, but now incorrectly converts the last line to lowercase.
$ cat file | awk '{IGNORECASE=1; if($1~/^ *baz/) print tolower($0); else print $0}'
foo Baz
baz qux
QUx Quux
baz qux
bazaar # ERROR HERE: should not be converted to lowercase, as keyword not present (emphasis on word!).
2 Answers
You already know about tolower() so just use it again in the comparison and test for an exact string match instead of partial regexp:
awk 'tolower($1)=="baz"{$0=tolower($0)}1'
Add word-boundary after search string
$ awk '{IGNORECASE=1; if($1~/^ *baz\>/) print tolower($0); else print $0}' ip.txt
foo Baz
baz qux
QUx Quux
baz qux
BazaaR
Can be re-written as:
awk 'BEGIN{IGNORECASE=1} /^ *baz\>/{$0=tolower($0)} 1' ip.txt
Since line anchor is used, no need to match with $1. The 1 at end will print the record, including any changes done
IGNORECASE and \> are gawk specific features. \y can be also used to match word boundary
With GNU sed
$ sed 's/^[[:blank:]]*baz\b.*/\L&/I' ip.txt
foo Baz
baz qux
QUx Quux
baz qux
BazaaR
[[:blank:]]will match space or tab characters\L&will lowercase the line\bis word boundaryIflag to match case-insensitively
