shell script 질문입니다.

`expr' supports pattern matching and other string operators. These have lower precedence than both the numeric and relational operators (in the next sections).
STRING : REGEX
     Perform pattern matching.  The arguments are coerced to strings
     and the second is considered to be a (basic, a la GNU `grep')
     regular expression, with a `^' implicitly prepended.  The first
     argument is then matched against this regular expression.
 
     If the match succeeds and REGEX uses `\(' and `\)', the `:'
     expression returns the part of STRING that matched the
     subexpression; otherwise, it returns the number of characters
     matched.
 
     If the match fails, the `:' operator returns the null string if
     `\(' and `\)' are used in REGEX, otherwise 0.
 
     Only the first `\( ... \)' pair is relevant to the return value;
     additional pairs are meaningful only for grouping the regular
     expression operators.
 
     In the regular expression, `\+', `\?', and `\|' are operators
     which respectively match one or more, zero or one, or separate
     alternatives.  SunOS and other `expr''s treat these as regular
     characters.  (POSIX allows either behavior.)

echo $conf | sed -e 's,^\(.\).*,\1,'