Let's assume the following variable:
something=" abc def ghi"
I'm trying to use parameter expansion and leave out only the abc. I've tried 10 combinations that made sense and 20 more randomly. The closest I got is the following:
echo ${something% *}
abc def
Is it possible for this to work out? If so, how? Thanks.
It's going to be tough in a single bash-expansion. You might be interested in this:
$ a=" abc def ghi"
$ [[ "${a}" =~ ([^\ ][^\ ]*) ]]
$ echo "${BASH_REMATCH[0]}"
This essentially searches for all words in the string and stores them in the array BASH_REMATCH. More information in man bash section [[ expression ]].
You can also convert things into an array:
$ a=" abc def ghi"
$ b=( $a )
$ echo "${b[0]}"
Or you can use read
$ a=" abc def ghi"
$ read -r b dummy <<< "${a}"
$ echo "${b}"
But if you really want to use parameter expansion, and you allow the usage of extglob and you do not know the number of words there are in the string, you can do
$ a=" abc def ghi"
$ shopt -s extglob
$ a=${a##*([ ])} #remove the spaces in the front
$ a=${a%% *} #remove everything from the first space onwards
$ echo "${a}"
If the string def is know upfront, you can use bash pattern substitution:
echo ${something/ def*/}
That's replacing everything after def by nothing.
You could also use the following if the string def is in the variable a:
a="def"
echo ${something/ ${a}*/}
If it's just the first whitespace-delimited word you want, use read.
read x _ <<< "${something}"
read takes the value of "${something}", and splits it into two words based on the current value of IFS; the first word (abc) is assigned to x, with the second word (consisting of all remains characters) assigned to the throwaway variable _.
$_ really throw-away? It's documented as doing a number of things at the bottom of Special Parameters in the man page, and has different uses in different contexts. I'm pretty sure it was throw-away in POSIX shell, but in bash ... perhaps not so much.
You can't do this in a single parameter expansion, instead, do this :
$ x=${something% def*}
$ echo ${x# *}
abc
${x# *} actually removes only one blank at the start of the string and again the shell wordsplitting does the rest. might as well have left that part out.With extglob
shopt -s extglob
echo ${something%%*( )*([^ ])*( )*([^ ])}
The substitution itself does not cut the leading blanks though, the shell word splitting does that. if you quote the argument to echo they will still be there.
The substitution removes the longest possible match for zero or more spaces followed by zero or more characters that are not spaces, followed again by zero or more spaces and zero or more not-spaces at the end of the string.
