Tip #542   Implementing join in bash

Implementing "join" in bash (python's join, php's implode, etc.).

NOTE: the $ means "type what follows at your terminal prompt" (some people thinks that the $ is part of the command).

$ list_join() { 
    local OLDIFS=$IFS
    IFS=${1:?"Missing separator"}; shift
    echo "$*"
    IFS=$OLDIFS
}

$ list_join : one two three
one:two:three

it only works for single characters, so this won't work as expected:

$ list_join ', ' one two three
one,two,three

:P

also notice that you need to pass the list expanded (hence the name "list_join") so if you have an array you do:

$ myarray=(one two three)

$ list_join : "${myarray[@]}"
one:two:three

this function is pretty handy to use with fgrep (grep -f); fgrep is faster than grep because it does not use regular expressions so unless you actually need a regexp it's best to use that instead of normal grep, fgrep also accepts several words to search at once and works like an OR operation (if you chain several greps you get an AND operation) the only problem is that fgrep expects you to separate the words by newlines -quite ugly- so you can use the function like this:

$ fgrep "$(list_join $'\n' samus root)" /etc/group
root::0:root
bin::1:root,bin,daemon
daemon::2:root,bin,daemon
sys::3:root,bin
adm::4:root,daemon
disk::6:root
wheel::10:root,samus
log::19:root
audio::92:samus
optical::93:hal,samus
storage:x:95:hal,samus