I’m writing a script to update some config files. One of the config file lines looks like this:
hosts: [localhost]
I’m using to do the substitutions which is working fine, but that line I can not figure out. When I use:
sed -E "s/(^hosts:s*)/1testing/" config.yaml
it returns:
hosts:testing [localhost]
It seems ok but s* did not not match the space. So I try:
sed -E "s/(^hosts:s+)/1testing/" config.yaml
and it doesn’t match at all. When I replace the s+ with an actual space it works and the full pattern:
sed -E "s/(^hosts: )[[A-Za-z.]*]/1testing/" config.yaml
hosts: testing
1
Standard sed with -E uses Extended Regular Expressions syntax with a few differences.
EREs do not treat s as a character class.
GNU sed, however, when not run with --posix does recognise it as such.
The standard way to specify the space character class is:
[[:space:]]
See: https://pubs.opengroup.org/onlinepubs/9799919799/basedefs/V1_chap09.html#tag_09_03_05