Insert Header Row using sed - sed

Question

I need to run a bash script via cron to update a file.
The file is a .DAT (similar to csv) and contains pipe separated values.
I need to insert a header row at the top.
Here's what I have so far:
#!/bin/bash
# Grab the file, make a backup and insert the new line
sed -i.bak 1i"red|blue|green|orange|yellow" thefilename.dat
Exit
But how can I save the file as a different file name so that it always takes fileA, edits it and then saves it as fileB

Answer 1

do you really rename the old one to xxx.bak or can you just save a new copy?
either way, just use redirection.
sed 1i"red|blue|green|orange|yellow" thefilename.dat > newfile.dat
or if you want the .bak as well
sed 1i"red|blue|green|orange|yellow" thefilename.dat > newfile.dat \
&& mv thefilename.dat thefilename.dat.bak`
which would create your new file and then, only if the sed completed sucessfully, rename the orig file.

Answer 2

In case anyone finds it useful, here is what I ended up doing....
Grab the original file, convert it to the desired file type, whilst inserting a new header row and making a log of this.
#!/bin/bash -l
####################################
#
# This script inserts a header row in the file $DAT and resaves the file in a different format
#
####################################
#CONFIG
LOGFILE="$HOME/bash-convert/log-$( date '+%b-%d-%y' ).log"
HOME="/home/rootname"
# grab original file
WKDIR="$HOME/public_html/folder1"
# new location to save
NEWDIR="$HOME/public_html/folder2"
# original file to target
DAT="$WKDIR/original.dat"
# file name and type to convert to
NEW="$NEWDIR/original-converted.csv"
####################################
# insert a new header row
HDR="header-row-1|header-row-2|header-row-2 \r"
# and update the log file
{
echo "---------------------------------------------------------" >> $LOGFILE 2>&1
echo "Timestamp: $(date "+%d-%m-%Y: %T") : Starting work" >> $LOGFILE 2>&1
touch "$LOGFILE" || { echo "Can't create logfile -- Exiting." && exit 1 ;} >>"$LOGFILE"
# check if file is writable
sudo chmod 755 -R "$NEW"
echo "Creating file \"$NEW\", and setting permissions."
touch "$NEW" || {
echo "Can't create file \"$NEW\" -- Operation failed - exiting" && exit 1 ;}
} >>"$LOGFILE" 2>&1
{
echo "Prepending line \"$HDR\" to file $NEW."
{ echo "$HDR" ; cat "$DAT" ;} > "$NEW"
{
if [ "$?" -ne "0" ]; then
echo "Something went wrong with the file conversion."
exit 1
else echo "File conversion successful. Operation complete."
fi
}
} >>"$LOGFILE" 2>&1
exit 0

Answer 3

I found more clear an consistent the syntax with 'i' between the two single quotes for the pattern to 'insert'.
You can simply add a header, and save it in a different file with:
sed '1i header' file > file2
In your case:
sed '1i red|blue|green|orange|yellow' file > file2
If you wanted to save it on the same file, you'd use -i option:
sed -i '1i red|blue|green|orange|yellow' file