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Shell script utility to read a file line line

Posted in File-management

#!/bin/bash
# Shell script utility to read a file line line.
# Once line is read it can be process in processLine() function
# You can call script as follows, to read myfile.txt:
# ./readline myfile.txt
# Following example will read line from standard input device aka keyboard:
# ./readline
# -----------------------------------------------
# Copyright (c) 2005 nixCraft <http://cyberciti.biz/fb/>
# This script is licensed under GNU GPL version 2.0 or above
# -------------------------------------------------------------------------
# This script is part of nixCraft shell script collection (NSSC)
# Visit http://bash.cyberciti.biz/ for more information.
# -------------------------------------------------------------------------
 
# User define Function (UDF)
processLine(){
  line="$@" # get all args
  #  just echo them, but you may need to customize it according to your need
  # for example, F1 will store first field of $line, see readline2 script
  # for more examples
  # F1=$(echo $line | awk '{ print $1 }')
  echo $line
}
 
### Main script stars here ###
# Store file name
FILE=""
 
# Make sure we get file name as command line argument
# Else read it from standard input device
if [ "$1" == "" ]; then
   FILE="/dev/stdin"
else
   FILE="$1"
   # make sure file exist and readable
   if [ ! -f $FILE ]; then
  	echo "$FILE : does not exists"
  	exit 1
   elif [ ! -r $FILE ]; then
  	echo "$FILE: can not read"
  	exit 2
   fi
fi
# read $FILE using the file descriptors
 
# Set loop separator to end of line
BAKIFS=$IFS
IFS=$(echo -en "\n\b")
exec 3<&0
exec 0<$FILE
while read line
do
	# use $line variable to process line in processLine() function
	processLine $line
done
exec 0<&3
 
# restore $IFS which was used to determine what the field separators are
BAKIFS=$ORIGIFS
exit 0

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Discussion on This Shell Script:

  1. vikas kale Says: June 14th, 2008 at 9:09 am

    good…….

  2. aye Says: July 19th, 2008 at 4:14 pm

    thanks!

  3. Brett Says: July 24th, 2008 at 7:29 pm

    Hey this worked perfectly. I used it to automatically patch my sun system. I used smpatch analyze > patch.txt then used your script to read in the outputed patch numbers.

  4. John Sanabria Says: August 7th, 2008 at 8:50 pm

    Excellent! very illustrative,

    thanks for your contribution! ;-)

  5. michelek Says: October 30th, 2008 at 12:10 pm

    bad news for everybody who has lines with more than one space between words.

  6. vivek Says: October 31st, 2008 at 2:16 pm

    @michelek,

    This can be easily fixed by adding following code before and after while loop:

    ORIGIFS=$IFS
IFS=$(echo -en "\n\b")
# add your while loop here
IFS=$ORIGIFS

    while / for / untile loop is using $IFS to determine what the field separators are. I’ve modified this to use end of line. Here is final modified code:

    ORIGIFS=$IFS
IFS=$(echo -en "\n\b")

exec 3< &0
exec 0<$FILE
while read line
do
	# use $line variable to process line in processLine() function
	processLine $line
done
exec 0<&3

IFS=$ORIGIFS

    The script has been updated to fix this issue. Just download updated version.

    HTH

  7. David Says: November 18th, 2008 at 3:34 pm

    Thank you so much, this is just what I was looking for :)

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Tags: , , , , , , , , , ~ Last updated on: October 31, 2008