Shell Script Utility To Read a File Line By Line

in File-management last updated September 21, 2009

#!/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

#!/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

# -----------------------------------------------

# 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

# 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

# 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

39 comment

Azaz says:
February 8, 2012 at 5:43 am
Cool, I found this script very useful. I modified this and used to make our syncronisation across servers fully automated. Great Job
cavin says:
November 10, 2011 at 7:16 am
THANK YOU for sharing the script..it’s very generous/kind sharing…THUMBS UP
anon says:
August 23, 2011 at 5:00 pm
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 says:
March 31, 2011 at 9:10 am
Hi,
You can try this simple code to read the file “file.txt” line-by-ine….
while read line
do
echo $line;
sleep 1;
done < file.txt
DIPANKAR GHOSH says:
January 31, 2011 at 12:53 pm
hi i want to update a port number in a file such like……
file content…..abc.cfg
# Temporary use by Boyajian. Thank you.
# Plz feel free to change as per ur need. Thnx – Ayan
###—SBJ_VIEW_NAME=devB_4140sdd
#SBJ_VIEW_NAME=bagay_dev_mts_1440sdd
SBJ_VIEW_NAME=devD_4018
#SBJ_VIEW_NAME=devD_4017
ACE_MATCH_SERVER_HOST=localhost
ACE_MATCH_SERVER_PORT=16711
ACE_JASI_SERVER_PORT=75675
ENT_CLIENT_HOSTS=localhost,imts1,charon
ENT_SERVER_PORT=45785
ENT_SERVER_HOST=imts1
ENT_VIRTUAL_MEMORY=1000000000
ENT_NUM_ACCUMULATORS=8
SBJ_NO_SIG_CHECK=1
AREA_PROD_BRANCH=s2010
now if i want to update the value of ACE_MATCH_SERVER_PORT from 16711 to 78777
what would be the code to do this stub? please give a solution at the earliest
CrackTheInterview says:
January 21, 2011 at 11:29 am
for line in cat abc.txt;do
touch path/$line
done
this 2 line is code enuff
SK says:
October 19, 2010 at 8:07 am
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 says:
August 23, 2010 at 10:16 am
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 says:
July 9, 2010 at 4:47 am
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 says:
May 14, 2010 at 8:31 pm
Thanks for posting it!!!
Sanjay says:
March 8, 2010 at 2:50 pm
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 says:
February 16, 2010 at 6:55 pm
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 says:
December 29, 2009 at 5:34 am
Thank you for the post!!
ijo says:
December 13, 2009 at 5:47 pm
THANK YOU VERY MUCH!!!
Hari says:
October 28, 2009 at 9:15 pm
I have used your example countless time when i wanted to write a quick hack. Thank You!

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