I need to replace value with new_value in strings
key:value
key: value
key: value
To get
key:new_value
key: new_value
key: new_value
Number of spaces after : is arbitrary. The regex to match would be key: *value.
How do I replace value with new_value in such strings preserving number of spaces with sed?
To clarify, key1:value or key:value1 do not match due to different key/value, so such strings are not altered.
Try -
sed 's/^\(key: *\)value/\1new_vale/' file
g at the end: sed '.../g' ?
g not required here. To understand what g does, try out the following two commands: foo="aaaa"; echo $foo | sed 's/a/X'; echo $foo | sed 's/a/X/g' You may use this sed to match all cases:
sed -E 's/^([[:blank:]]*key[[:blank:]]*:[[:blank:]]*)value([[:blank:]]|$)/\1new_value/' file
key:new_value
key: new_value
key: new_value
This allows 0 or more whitespaces at:
key at startkey and :: and valuevalue before end[[:blank:]] matches a space or a tabg at the end: sed -E '.../g' ?
/g at the end
g is for when you need to process multiple matches on a line. Per the sample input in your question you don't have any cases where there are multiple matches on a line and so specifying g wouldn't make sense. If that's wrong then, of course, fix the example in your question.