Shell Programming and Scripting

while read line; do echo ${line:0:1} >>output.txt; done<input.txt

 sed -r 's/^(.).*/\1/' file

$ cat infile
begin
   two
   4-Fun
end
 
$ cut -c1 infile
b
 
e
 
$ sed 's/^[ \t]*\(.\).*/\1/' infile
b
t
4
e
 
$ sed 's/^[^a-zA-Z]*\([a-zA-Z]\).*/\1/' infile
b
t
F
e

$ sed 's/^[^[:alpha:]]*\([[:alpha:]]\).*/\1/'  infile
b
t
F
e
$

   sed -r 's/^(.).*/\1/' file  
sed -rn 's/^[[:space:]]*([[:alpha:]]).*/\1/p' file

awk '{print substr($1,1,1)}' infile

cut -c 1 < infile