Bash

Neville Hillyer · 04-11-2017, 10:13 AM

In Bash I use y=$(<tmp) to put the contents of a file into a string but I was caught out today with a JavaScript file starting with /*

Here is a test case you can try:

echo '/*' > tmp; y=$(<tmp); echo $y

This could be dangerous. How should it be overcome especially for files with unknown content?

Guttorm · 04-11-2017, 10:17 AM

Add quotes around variables when you used them.

echo '/*' > tmp; y=$(<tmp); echo "$y"

pan64 · 04-11-2017, 10:25 AM

just a comment: echo '/*' > tmp; y=$(<tmp); worked perfectly, so the variable y contained what you wanted/expected, only the last part was "strange": echo $y does not (only) print the value of y but first it was evaluated by bash. If you want to avoid that use " as it was explained in post #2

Ramurd · 04-11-2017, 10:40 PM

for that, and other reasons, it's good to make a habit out of placing quotes and braces around variables. Makes your code look more cosistent.

See the difference in code:

Code:

echo '/*' > /tmp/testfile
y="$(</tmp/testfile)"
echo "${y}"
echo "-----"
echo "$y"
echo "-----"
echo '${y}'
echo "-----"
echo $y

notice the difference what each type of quotes does btw; at times that can be handy.

Neville Hillyer · 04-12-2017, 04:39 AM

Quote:

Originally Posted by Guttorm

Add quotes around variables when you used them.

echo '/*' > tmp; y=$(<tmp); echo "$y"

How silly of me - thanks - "$y" works.

I thought I had tried this but clearly something went wrong. It was a small part in a larger script but clearly I did not adequately test my own simplified demonstration script.

grail · 04-12-2017, 10:21 AM

NEVER read a file using a for loop that has unknown content. Use a while loop.

BW-userx · 04-12-2017, 10:24 AM

for more on that look here if you think you are ready for "Advanced Bash-Scripting"
5.1. Quoting Variables