Shell Programming and Scripting

newname=`head -c 3 $filename`
tail -c +3 $filename > $newname

 
for i in `cat temp.txt`
do
v_substr=`expr substr "$i" 1 3`
if [ $v_substr = "abc" ]
then
echo "file contains abc"
echo $i >> file.txt
fi
done

grep "^abc" file.txt > file_with_abc.txt
grep -v "^abc" file.txt > file_without_abc.txt

whole_line=`head -1 $input_file`
data_portion="${whole_line##???}"                     # Get everything except first 3 chars
three_chars="${whole_line%$data_portion}"             # Get everything except the data portion
target_file="header_bit${three_chars}trailer_bit"     # Add anything required to build the target file name
echo $data_portion>$target_file                       # Chose overwrite or append carefully here

tail +2 $input_file > $tmp_file                       # Get record 2 and onward.  2 steps required
cat $tmp_file > $input_file                           # else you open $input_file for output
                                                      # before you have the data to write and 
                                                      # you will null the file.

echo "dd:wq" | vi $input_file

for whole_line in `cat $input_file`
do
   data_portion="${whole_line##???}"                  # Get everything except first 3 chars
   three_chars="${whole_line%$data_portion}"          # Get everything except the data portion
   target_file="header_bit${three_chars}trailer_bit"  # Add anything required to build the target file name
   echo $data_portion >> $target_file                 # Always append or you only get the last match!
done

typeset -i counter=1
total_lines=`wc -l $input_file`
while [ $counter -le $total_lines]
do
   whole_line=`sed -n ${counter}p $input_file`
   data_portion="${whole_line##???}"                  # Get everything except first 3 chars
   three_chars="${whole_line%$data_portion}"          # Get everything except the data portion
   target_file="header_bit${three_chars}trailer_bit"  # Add anything required to build the target file name
   echo $data_portion >> $target_file                 # Always append or you only get the last match!
   ((counter=$counter+1))
done

for three_chars in `cut -c -3 $input_file|sort -u`
do
   target_file="header_bit${three_chars}trailer_bit"  # Add anything required to build the target file name
   > $target_file                                     # or substitute rm for the >
done

echo "$target_file $counter\r\c" >&2

for three_chars in `cut -c -3 $input_file|sort -u`
do
   target_file="header_bit${three_chars}trailer_bit"  # Add anything required to build the target file name
   for whole_line in `grep $three_chars $input_file`
   do
      data_portion="${whole_line##???}"                  # Get everything except first 3 chars
      echo $data_portion
   done   > $target_file                  # Overwrite to negate the need to reset previous runs
done

for three_chars in `cut -c -3 $input_file|sort -u`
do
   target_file="header_bit${three_chars}trailer_bit"  # Add anything required to build the target file name
   grep $three_chars $input_file|cut -c 3- > $target_file
done

$ cat script.sed
/^abc/I {
  w newfile
}
/^abc/I! {
  p
}

$ sed -i -nf script.sed infile

 
ABC ddd 343 1299 
ABC ddd 3564 1299
CDE ddd 3297 1393
CDE ddd 32989 1527
DEF ddd 346498 1652
DEF ddd 3269 1652
etc...

 
ABC ddd 343 1299 
ABC ddd 3564 1299

 
CDE ddd 3297 1393
CDE ddd 32989 1527

 
DEF ddd 346498 1652
DEF ddd 3269 1652