Shell Script Utility To Read a File Line By Line

#!/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 -r line
do
	# use $line variable to process line in processLine() function
	processLine $line
done
exec 0<&3
 
# restore $IFS which was used to determine what the field separators are
IFS=$BAKIFS
exit 0
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39 comments… add one
  • Azaz Feb 8, 2012 @ 5:43

    Cool, I found this script very useful. I modified this and used to make our syncronisation across servers fully automated. Great Job

  • cavin Nov 10, 2011 @ 7:16

    THANK YOU for sharing the script..it’s very generous/kind sharing…THUMBS UP

  • anon Aug 23, 2011 @ 17:00

    Don’t listen that fool Dedeepthi ↑
    Here is the real code:
    —–cut here—————
    #!/bin/bash
    for i in ‘cat file.txt’
    do
    echo “$i”
    done
    —–cut here—————

  • Dedeepthi Mar 31, 2011 @ 9:10

    Hi,
    You can try this simple code to read the file “file.txt” line-by-ine….

    while read line
    do
    echo $line;
    sleep 1;
    done < file.txt

  • DIPANKAR GHOSH Jan 31, 2011 @ 12:53

    hi i want to update a port number in a file such like……
    file content…..abc.cfg

    # Temporary use by Boyajian. Thank you.
    # Plz feel free to change as per ur need. Thnx – Ayan
    ###—SBJ_VIEW_NAME=devB_4140sdd
    #SBJ_VIEW_NAME=bagay_dev_mts_1440sdd
    SBJ_VIEW_NAME=devD_4018
    #SBJ_VIEW_NAME=devD_4017
    ACE_MATCH_SERVER_HOST=localhost

    ACE_MATCH_SERVER_PORT=16711

    ACE_JASI_SERVER_PORT=75675
    ENT_CLIENT_HOSTS=localhost,imts1,charon
    ENT_SERVER_PORT=45785
    ENT_SERVER_HOST=imts1
    ENT_VIRTUAL_MEMORY=1000000000
    ENT_NUM_ACCUMULATORS=8
    SBJ_NO_SIG_CHECK=1
    AREA_PROD_BRANCH=s2010

    now if i want to update the value of ACE_MATCH_SERVER_PORT from 16711 to 78777
    what would be the code to do this stub? please give a solution at the earliest

  • CrackTheInterview Jan 21, 2011 @ 11:29

    for line in `cat abc.txt`;do
    touch path/$line
    done

    this 2 line is code enuff

  • SK Oct 19, 2010 @ 8:07

    Hi Very informative post. Thanks for this.
    But I have one confussion that
    what following code is doing. Please healp.
    BAKIFS=$IFS
    IFS=$(echo -en “\n\b”)
    exec 3<&0
    exec 0<"$FILE"

  • Vimarsh Aug 23, 2010 @ 10:16

    Guys,

    I need to read a file and see for the occurence /local/svncheckout/* at the begining of each line. If this instance is found I need to delete that particular line.

    I need to write this program using shell script (bash shell)

    Thanks a lot

  • sj Jul 9, 2010 @ 4:47

    I edited the code to input the contents of $line when ever the loop runs. it inputs line by line in a file that contains a list of id’s I pulled out of etc/passwd. for some reason it’s stops at the 25th line. it starts combining the variables to I dont’ know what’s going on. how it could work for the first 25 entries then break.

  • Samuel May 14, 2010 @ 20:31

    Thanks for posting it!!!

  • Sanjay Mar 8, 2010 @ 14:50

    Thank you for the post.
    It’s work perfectly but i need some changes
    can u help me?
    i want a search a specific pattern in a file and copy a a search result to xml file
    Thanks in advance.

  • vinu Feb 16, 2010 @ 18:55

    This is not working for me.

    sh read.sh v1.txt
    : not found:
    v1.txt
    : not found: }
    : not found:
    : not found:
    read.sh: 40: Syntax error: “elif” unexpected (expecting “then”)

  • Thushara Dec 29, 2009 @ 5:34

    Thank you for the post!!

  • ijo Dec 13, 2009 @ 17:47

    THANK YOU VERY MUCH!!!

  • Hari Oct 28, 2009 @ 21:15

    I have used your example countless time when i wanted to write a quick hack. Thank You!

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