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FalcoGer avatar Ubuntu

bash concatenate string in loop results in empty string

mx flag
FalcoGer

I have the following file

Hello
World
my
name
is
FalcoGer

And I wish to concatenate the strings of each line.

I wrote the following script to do just that.

#! /usr/bin/bash
myFile=/home/FalcoGer/testfile.txt

result=""
cat $myFile | while read line
do
  result+="$line "
done

echo Result: $result

However I only get Result: with an empty string. When I print it from within the loop it seems to work just fine. What's wrong with this script and how do I fix it?

234
1 + 8
uz flag
Jos
You can't concatenate strings like that in bash. Try `result="$result $line"` .
0
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hr flag
steeldriver
See [Why is my variable local in one 'while read' loop, but not in another seemingly similar loop?](https://unix.stackexchange.com/questions/9954/why-is-my-variable-local-in-one-while-read-loop-but-not-in-another-seemingly)
1
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FalcoGer avatar
mx flag
FalcoGer
@Jos yes you can. `+=` is a valid operator in bash. https://stackoverflow.com/questions/4181703/how-to-concatenate-string-variables-in-bash
3
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waltinator avatar
it flag
waltinator
Always paste your script into `https://shellcheck.net`, a syntax checker, or install `shellcheck` locally. Make using `shellcheck` part of your development process. Also, the blank on the first line is wrong. Use "`#!/bin/bash`".
0
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uz flag
Jos
Today I learned :-)
0
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hr flag
steeldriver
BTW I assume you're just using this as an exercise to learn about loops - if not, there are better options such as `result=$(paste -sd ' ' < myFile)` or (if you want to use shell constructs only, perhaps `readarray -t arr < myFile; result=${arr[*]}`
1
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FalcoGer avatar
mx flag
FalcoGer
@steeldriver actually i use this to download workshop content from steamcmd using a text file. I just broke it down for the minimum example. I prefer to have readable syntax over short one. I need to process the `$line` in any case, so I need a loop.
0
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hr flag
steeldriver
If you need to process the lines, that's usually even more of a reason **not** to use a shell loop. See for example [Why is using a shell loop to process text considered bad practice?](https://unix.stackexchange.com/questions/169716/why-is-using-a-shell-loop-to-process-text-considered-bad-practice)
0
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Score:4
FalcoGer avatar Ubuntu
mx flag
FalcoGer

Using the pipe essentially creates a new script with a new scope. You can avoid the pipe like so:

#! /usr/bin/bash
myFile=/home/FalcoGer/testfile.txt

result=""
while read -r line
do
  result+="$line "
done < $myFile

echo Result: $result
0 + 3
cn flag
glenn jackman
This is [BashFAQ 24](http://mywiki.wooledge.org/BashFAQ/024)
1
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bac0n avatar
cn flag
bac0n
You usually want to add `-r` to read.
1
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FalcoGer avatar
mx flag
FalcoGer
@bac0n it would appear so.
0
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