BASH append to middle of file

baks · 02-26-2007, 05:55 PM

HI, Im new to this forum and would like some help. I have created the following script which takes two arguments from the commandline and inputs the text from the first argument into the top line of the second argument(a file).

INPUT=$1
FIRSTLINEF=$2
TEMPFILE=TEMP

echo $INPUT > $TEMPFILE # User input will be placed in the temp file
cat $FIRSTLINEF >> $TEMPFILE # Contents of original file will be added
mv -f TEMP firstlinefile # Temp file will replace original file

I just have one question. How would I place the text entered at the commandline into the middle of a file. How would I manage it ?

I know I need to count the lines in the file and then use another temp file but Im completely lost.

I also cant use SED or AWK.

Thank You in advance.

jschiwal · 02-26-2007, 06:03 PM

Why don't you want to use sed or awk?

You could look into using the wc command to count lines, and the head and tail commands to disect a file on a certain line.

jr1 · 02-26-2007, 06:58 PM

Quote:

Originally Posted by baks

echo $INPUT > $TEMPFILE # User input will be placed in the temp file
cat $FIRSTLINEF >> $TEMPFILE # Contents of original file will be added
mv -f TEMP firstlinefile # Temp file will replace original file

I'd replace that with this

Code:

echo $INPUT | cat - $FIRSTLINEF > $OUTFILE

Quote:

I just have one question. How would I place the text entered at the commandline into the middle of a file. How would I manage it ?

I know I need to count the lines in the file and then use another temp file but Im completely lost.

I also cant use SED or AWK.

Consider using perl or awk or sed or even ed. Otherwise, maybe something like this (as long as you're using bash)

Code:

echo $INPUT | cat <(head -$N $FILE) - <(tail -n +$((N+1)) $FILE) > $OUTFILE

Or, for a pure shell-based approach you could use a while loop or for loop. One example:

Code:

i=1; cat $FILE | while read line
do
    echo $line
    [ $i -eq $N ] && echo $INPUT
    i=$((i+1))
done > $OUTFILE; unset i

cfaj · 02-27-2007, 05:40 PM

Quote:

Originally Posted by baks

HI, Im new to this forum and would like some help. I have created the following script which takes two arguments from the commandline and inputs the text from the first argument into the top line of the second argument(a file).

INPUT=$1
FIRSTLINEF=$2
TEMPFILE=TEMP

echo $INPUT > $TEMPFILE # User input will be placed in the temp file
cat $FIRSTLINEF >> $TEMPFILE # Contents of original file will be added
mv -f TEMP firstlinefile # Temp file will replace original file

I just have one question. How would I place the text entered at the commandline into the middle of a file. How would I manage it ?

What do you mean by "middle"? Do you mean the exact middle of the file, and, if so, do you mean by character or by line?

Quote:

I know I need to count the lines in the file and then use another temp file but Im completely lost.

I also cant use SED or AWK.

Why not? They are the logical tools to use.

To put something in the middle of the file, counting bytes rather than lines:

Code:

middle=$(( $( wc -c < FILENAME ) / 2 ))
{
  dd bs=$middle count=1 2>/dev/null
  printf "%s" "$INPUT"
  cat
} < FILENAME > TEMPFILE

To put it in the middle by line:

Code:

middle=$(( $( wc -l < FILENAME ) / 2 ))
n=0
{
  while [ $n -le $middle ]
  do
    IFS= read -r line
    printf "%s\n" "$line"
    n=$(( $n + 1 ))
  done
  printf "%s\n" "$INPUT"
  cat
} < FILENAME > TEMPFILE

baks · 02-28-2007, 03:27 AM

I have managed to complete the task. I used the head and tail command together with count to be able to determine the number of lines and then used a temporary file.

I was not allowed to use SED or AWK, dont really know why.

Thank you everyone for helping me.