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

 

 

The following example script takes a regular expression as its first argument and one or more strings to match against. It then cycles through the strings and outputs the results of the match process:

#!/bin.bashif [[ $# -lt 2 ]]; then    echo "Usage: $0 PATTERN STRINGS..."    exit 1firegex=$1shiftecho "regex: $regex"echowhile [[ $1 ]]do    if [[ $1 =~ $regex ]]; then        echo "$1 matches"        i=1        n=${#BASH_REMATCH[*]}        while [[ $i -lt $n ]]        do            echo "  capture[$i]: ${BASH_REMATCH[$i]}"            let i++        done    else        echo "$1 does not match"    fi    shiftdone

 

Assuming the script is saved in "bashre.sh", the following sample shows its output:

  # sh bashre.sh 'aa(b{2,3}[xyz])cc' aabbxcc aabbcc  regex: aa(b{2,3}[xyz])cc  aabbxcc matches    capture[1]: bbx  aabbcc does not match