bash + sed: quadruple backslash for proper escaping within an alias
Posted by jpluimers on 2020/06/09
This is part of a bash alias where I had to use quadruple backslash in order to escape it for sed:
# The sed with quad //// is to prevent 'unterminated substitute in regular expression':
alias x='... | sed "s/=.*/ \\\\/"'
This is needed because bash will escape \\\\ into \\ which sed then escapes to \.
The easiest way to find this is to replace the sed with echo to see the expansion.
References:
- explanation at [WayBack] regex – Why does sed require 3 backslashes for a regular backslash? – Stack Overflow (by Dennis Williamson).
- echo tip at [WayBack] regex – Why does sed require 3 backslashes for a regular backslash? – Stack Overflow (byRoger Pate who left StackOverflow).
–jeroen
The Wiert Corner - irregular stream of stuff 
Mike Verhagen said
“This is needed because bash will escape \\ into \ which sed then escapes to .”
this makes me smile….when you know you have just one level of indirection, it’s s genius move.
jpluimers said
After swearing, then figuring out, I had to smile too (: