How can I read a file into a variable in bash

Question

I want to store the contents of a file in a bash shell variable. This works fine:

$ cat hello
Hello, world!
$ F=hello
$ Q=$(cat $F)
$ echo $Q
Hello, world!

However, if the file contains an asterisk, the asterisk is replaced by a list of all files in the current directory.

How can I quote the filename to protect the asterisk? Or otherwise load the file into the shell variable?

I am aware of this question, but it doesn't work for files that contain an asterisk.

The next question: what if the _filename_ contains a space? `mv hello "hello world"; F="hello world"` -- what happens when you do `Q=$(cat $F)` ? — glenn jackman, Apr 06 '21 at 21:08
Note, bash has a builtin way to read a file into a variable: `Q=$(<"$F")` -- documented in [3.5.4 Command Substitution](https://www.gnu.org/software/bash/manual/bash.html#Command-Substitution) — glenn jackman, Apr 06 '21 at 21:11

score 4 · Accepted Answer · answered Apr 06 '21 at 19:45

Q contains the asterisk. It is the unquoted expansion of $Q that replaces the * with a list of files.

$ Q="*"
$ echo $Q
<list of files>
$ echo "$Q"
*

The right-hand side of an assignment is not subject to path name expansion, so Q=* would work as well, and the command substitution used to read from the file is also not affected. Q=$(cat hello) works fine: you just need to quote the expansion of Q.

How can I read a file into a variable in bash

1 Answers1