I have the following string and I want to replace (remove) the second word that appears in the string (SECONDWORD). The following line doesn't change anything and just prints the same string. However, when I remove the '123' part of the string the line seems to work.
echo "WORD 123 SECONDWORD THIRDWORD" | sed 's/ *[A-Z]* *//2'
I don't see the problem.
Try this: sed -r 's/\b[A-Z]+ *//2
The *, which matches zero occurences, is the issue.
You can see this by playing with the trailing number. When you have space separated strings that don't match [A-Z], you get matches on empty strings that delimit unmatched strings.
[~/tmp] > echo 'WORD 123 SECONDWORD THIRDWORD FOURTHWORD' | sed 's/ *[A-Z]* *//1'
123 SECONDWORD THIRDWORD FOURTHWORD
[~/tmp] > echo 'WORD 123 SECONDWORD THIRDWORD FOURTHWORD' | sed 's/ *[A-Z]* *//2'
WORD 123 SECONDWORD THIRDWORD FOURTHWORD
[~/tmp] > echo 'WORD 123 SECONDWORD THIRDWORD FOURTHWORD' | sed 's/ *[A-Z]* *//3'
WORD 123 SECONDWORD THIRDWORD FOURTHWORD
[~/tmp] > echo 'WORD 123 SECONDWORD THIRDWORD FOURTHWORD' | sed 's/ *[A-Z]* *//4'
WORD 123THIRDWORD FOURTHWORD
[~/tmp] > echo 'WORD 123 SECONDWORD THIRDWORD FOURTHWORD' | sed 's/ *[A-Z]* *//5'
WORD 123 SECONDWORD FOURTHWORD
... so when you have 123 in there you actually want the 4th matching item removed. Where 'WORD ', null, null,' SECONDWORD ','THIRDWORD ' are matching patterns 1-5. It's matching two empty strings around the boundaries of 123.
You can fix this by using + and not * with sed -r:
[~/tmp] > echo 'WORD 123 SECONDWORD THIRDWORD FOURTHWORD' | sed -r 's/ *[A-Z]+ *//2'
WORD 123THIRDWORD FOURTHWORD
Or use the uglier \{1,\} syntax without -r:
[~/tmp] > echo 'WORD 123 SECONDWORD THIRDWORD FOURTHWORD' | sed 's/ *[A-Z]\{1,\} *//2'
WORD 123THIRDWORD FOURTHWORD
But that ate a space you didn't want eaten, so used the \b word boundary marker:
[~/tmp] > echo 'WORD 123 SECONDWORD THIRDWORD FOURTHWORD' | sed -r 's/\b[A-Z]+ *//2'
WORD 123 THIRDWORD FOURTHWORD
This might work for you (GNU sed):
sed 's/\S\+\s*//2' file
Remove the second occurrence of one or more non-spaces followed by zero or more spaces.
May also be written:
sed 's/\S\S*\s*//2' file
