Glob pattern for replacing two or more spaces followed by some text within a string

Question

I want to construct a glob pattern that matches two spaces or more followed by some text on a line of text for pattern replacement.

For instance, consider the following string

str="Here is a list of functions  Marionette Recutils"

I want to replace the last part consisting of two or more spaces followed by some text. That in a glob pattern matching " Marionette Recutils".

I want a pattern that matches two or more spaces followed by some text. Have come up with the following pattern

ptrn="[[:blank:]]+([[:blank:]])+([[:graph:]])"

Can the pattern for parameter substitution match a substring, allowing both leading and trailing characters to exist?

Answer 1

For two or more of something, with glob patterns, you can use:

• {2,}(something) in ksh93
• (something)(#c2,) in zsh -o extendedglob.
• something(something)## in zsh -o extendedglob.
• something+(something) in ksh or bash -O extglob (or zsh --emulate ksh).
• somethingsomething*(something) in those as well.

So in bash:

shopt -s extglob
str="Here is a list of functions  Marionette Recutils"
newstr=${str/ +( )*/REPLACEMENT}

Or

newstr=${str/[[:blank:]]+([[:blank:]])*/REPLACEMENT}

In POSIX sh, you could also do:

case str in
  (*[[:blank:]][[:blank:]]*) newstr=${str%%[[:blank:]][[:blank:]]*}REPLACEMENT;;
  (*) newstr=$str;;
esac

The ${str%%pattern} operator (initially from ksh) removes the longest string that matches the pattern at the end of $str.

Answer 2

I'm fairly certain this will not handle several edge cases, but I was successful with this...

# echo "Here is a list of functions  Marionette Recutils" | sed "s/  .*//"

Here is a list of functions

Answer 3

Brief: In Pure Bash: out=${str/* /}

Long:

str="Here is a list of functions  Marionette Recutils"
echo "${str/*  /}"   # <-- This way
# Out: Marionette Recutils

From man bash / Parameter Expansion

${parameter/pattern/string}

Pattern  substitution.   The pattern is expanded to produce a
pattern just as in pathname expansion, Parameter is  expanded
and  the  longest  match  of pattern against its value is re‐
placed with string.

Answer 4

The confusing thing about character classes like [:blank:] is that they go inside of bracket expressions, so the whole thing has two concentric sets of brackets: [[:blank:]]. This also means you can combine them, like [[:blank:][:lower:]] (a single blank or lower-case letter) or [-_[:alpha:]] (a dash, underscore, or letter), or negate them like [^[:blank:]] (any character that isn't a blank).

So, you could use something like this:

ptrn="[[:blank:]][[:blank:]]*"
echo "${str%$ptrn}"

or just:

echo "${str%[[:blank:]][[:blank:]]*}"