Reverse Strings in a Text File

From Notes

Bash

When using Bash, the method that I have come up with is to read the file, line by line, and then prepend each line to a newly created file. This method uses a significant amount of disk I/O and could use some refinement.

An example follows (validation removed for brevity):

#!/bin/bash

# create file to write output to
OUTFILE="${1}_reversed_$$"
STAGING="${1}_staging_$$"

# create outfile and prime with a single line
# to allow sed to work (otherwise there would not be anything to prepend)
echo "test" > ${OUTFILE}

# Switch IFS to newline rather than white space
ifs=${IFS}
IFS='\
'

# open file descriptor to input file
exec 3< $1

START=0

# iterate through file
while read -u 3 LINE
do

# insert line from file before 1st line in outfile
sed '1 i\
'"${LINE}"'' ${OUTFILE} > ${STAGING}

       mv ${STAGING} ${OUTFILE}

  # remove the last line from the outfile
       # cleans up 'test'
       if [ ${START} -lt 1 ]
       then
    sed -i '$d' ${OUTFILE}
               START=1
       fi
done

# restore white space IFS
IFS=${ifs}

exit 0