Ttdfjt

Say I have a variable var whose value is fOo bar1 baR2 bArab.

How do I go about saving into another variable, say, lc_var, a version of var where all but the first word are converted to lowercase?

I know it can look something like lc_var=$(echo $var | ...), where ... will replaced by an appropriate AWK or sed command.

With the zsh shell:

set -o extendedglob
lc_var=$var/%(#m) */$(L)MATCH

Where $var/%pattern/replacement like in ksh replaces the end of the var that matches the pattern with the replacement, (#m) causes the matched portion to be stored in $MATCH (that's the part that needs extendedglob) and $(L)MATCH converts $MATCH to lowercase.

With the bash shell:

tmp1=$var%% *
tmp2=$var#"$tmp1"
lc_var=$tmp1$tmp2,,

POSIXly, you'd do:

lc_var=$(
 awk '
 BEGIN
 var = ARGV[1]
 if (i = index(var, " "))
 var = substr(var, 1, i) tolower(substr(var, i + 1))
 print var "."
 ' "$var"
)
lc_var=$lc_var%.

In any case, that can't look like lc_var=$(echo $var ...) because $(...) is POSIX/Korn/bash/zsh shell syntax, and in those shells, echo can't output arbitrary data and variable expansions should be quoted (except maybe in zsh).

All those variants turn to lower case all the characters past the first space character in $var (making no assumption on what characters they may be). You'd need to adapt it if words are possibly delimited by characters other than space, or if there may be word delimiter characters before the first word.

With bash:

var='fOo bar1 baR2 bArab'
tail=$var#* ; lc_var="$var%% * $tail,,"
echo "$lc_var"

fOo bar1 bar2 barab

as a function:

set_lc() declare -n v=$1; declare t=$2#* ; v="$2%% * $t,,"; 

or:

set_lc() typeset -n _v=$1; typeset h=$2%% *; typeset -l t=$2#"$h"; _v=$h$t; 

(this 2nd version should also work in ksh, and will handle an argument made up of a single word)

set_lc var 'FOO BAR BAZ'
echo "$var"

FOO bar baz

More info about bash's weird and limited parameter expansion modifiers and about declare / typeset in the bash manual.

The following solution uses GNU sed and was tested in bash only. It works even if the variable contains multi-line text.

lc_var="$(printf "%sn" "$var"|sed ':l;$!N;bl;s:s.*:L&.:')"
lc_var="$lc_var%."

Many thanks to @Stéphane Chazelas for the discussion about edge cases, like echo, sed -z, command substitution and other things.

lc_var=$(echo $var | sed 's/^([^ ]*)(.*)/1L2/g')

(with a little help from http://timmurphy.org/2013/02/24/converting-to-uppercase-lowercase-in-sed/)