Comments on Can I enter raw strings in fish to avoid escaping regexes for sed?
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Can I enter raw strings in fish to avoid escaping regexes for sed?
When running sed through fish, I often encounter a problem with regexes. Many commonly used regex control characters like []{}().+ need to be escaped, even if I type the regex in a single quoted string. For example:
$ echo abc | sed 's/b+/X/'
abc
$ echo abc | sed 's/b\+/X/'
aXc
This constant \ in front of many characters makes my regexes absolutely unreadable. It gets even worse if the regex itself needs to escape characters, the whole thing becomes a jumble of backslashes.
Surely there's a better way to enter complex strings in the shell? I don't know if this is a fish problem, or a generic shell problem, or a sed problem, but I would love to know how to avoid it.
As an example of what I expect: Python has an elegant solution to this, called "raw strings". r"b+" is therefore interpreted without any formatting or templating at all. Is there a raw string option in fish, or other shells? Does sed have an alternate input mode to get around this annoying problem?
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It is not the most elegant solution, but you may be able to use the string escape function of fish, as in:
echo abc | sed -E (string escape 's/b+/X/')
This would still escape the special characters, but in a "hidden" way - the user-visible RegEx is not cluttered with backslashes and the sed command sees the result of the command substitution, which is properly escaped.
So far, I don't know of any shell that has a feature to turn off interpretation of special characters (if anyone knows, it would likely be Stéphane Chazelas over at U&L SE).
Note that the + metacharacter is extended regular expression syntax, which sed doesn't understand unless invoked with the -E option. When called "bare", it uses basic regular expressions, where the "one or more" would need to be expressed explicitly using range indicators, so you would need to write
echo abc | sed (string escape 's/b\{1,\}/X/')
where the \ are now an actual part of the RegEx and therefore indispensable.
Update: A comment by @Quasímodo notified me that the GNU extension of BRE as used by GNU sed actually does implement the + quantifier, but - similar to { and } - it must be given its special meaning by preceding it with a \. So in this case the \ is an integral part of the RegEx and must be literally passed to sed in the form b\+ if you don't want to invoke it with -E to make use of ERE.
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