Shell Script Utility To Read a File Line By Line

by Vivek Gite on April 9, 2008

#!/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

Tagged as: args, bash read file, bash read file line by line, bash read from file, bash read line, command line argument, exec, f1, fi fi, how to reads a file using shell script, keyboard, loop method, read file in shell script, read file shell script, reading a file in shell script, readline, shell script read file, shell script read from file, standard input device, while loop

{ 39 comments… add one }

Previous Comments

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

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