bash while loop "eats" my space characters - bash

Question

I am trying to parse a huge text file, say 200mb.
the text file contains some strings
123
1234
12345
12345
so my script looked like
while read line ; do
echo "$line"
done <textfile
however using this above method, my string " 12345" gets truncated to "12345"
I tried using
sed -n "$i"p textfile
but the the throughput is reduced from 27 to 0.2 lines per second, which is inacceptable ;-)
any Idea howto solve this?

Answer 1

You want to echo the lines without a fieldsep:
while IFS="" read line; do
echo "$line"
done <<< " 12345"
When you also want to skip interpretation of special characters, use
while IFS="" read -r line; do
echo "$line"
done <<< " 12345"
You can write the IFS without double quotes:
while IFS= read -r line; do
echo "$line"
done <<< " 12345"

Answer 2

This seems to be what you're looking for:
while IFS= read line; do
echo "$line"
done < textfile
The safest method is to use read -r in comparison to just read which will skip interpretation of special characters (thanks Walter A):
while IFS= read -r line; do
echo "$line"
done < textfile

Answer 3

OPTION 1:
#!/bin/bash
# read whole file into array
readarray -t aMyArray < <(cat textfile)
# echo each line of the array
# this will preserve spaces
for i in "${aMyArray[#]}"; do echo "$i"; done
readarray -- read lines from standard input
-t -- omit trailing newline character
aMyArray -- name of array to store file in
< <() -- execute command; redirect stdout into array
cat textfile -- file you want to store in variable
for i in "${aMyArray[#]}" -- for every element in aMyArray
"" -- needed to maintain spaces in elements
${ [#]} -- reference all elements in array
do echo "$i"; -- for every iteration of "$i" echo it
"" -- to maintain variable spaces
$i -- equals each element of the array aMyArray as it cycles through
done -- close for loop
OPTION 2:
In order to accommodate your larger file you could do this to help alleviate the work and speed up the processing.
#!/bin/bash
sSearchFile=textfile
sSearchStrings="1|2|3|space"
while IFS= read -r line; do
echo "${line}"
done < <(egrep "${sSearchStrings}" "${sSearchFile}")
This will grep the file (faster) before it cycles it through the while command. Let me know how this works for you. Notice you can add multiple search strings to the $sSearchStrings variable.
OPTION 3:
and an all in one solution to have a text file with your search criteria and everything else combined...
#!/bin/bash
# identify file containing search strings
sSearchStrings="searchstrings.file"
while IFS= read -r string; do
# if $sSearchStrings empty read in strings
[[ -z $sSearchStrings ]] && sSearchStrings="${string}"
# if $sSearchStrings not empty read in $sSearchStrings "|" $string
[[ ! -z $sSearchStrings ]] && sSearchStrings="${sSearchStrings}|${string}"
# read search criteria in from file
done <"${sSearchStrings}"
# identify file to be searched
sSearchFile="text.file"
while IFS= read -r line; do
echo "${line}"
done < <(egrep "${sSearchStrings}" "${sSearchFile}")