How can I read a file and redirect it to a variable?

Question

I have a file with a word written on it. I want my script to put that word in a variable.

How can I do that?

wich · Accepted Answer · 2011-01-20T16:50:44.560

114

in several of a million ways...

simplest is probably

my_var=$(cat my_file)

If you use bash and you want to get spiffy you can use bash4's mapfile, which puts an entire file into an array variable, one line per cell

mapfile my_var < my_file

edited Jan 20 '11 at 16:50

answered Jan 20 '11 at 16:43

wich

Since when is spacing before and after `=` allowed in shell scripting? – orlp Jan 20 '11 at 16:44
1

@nightcracker sorry, brainfart, I had already corrected it before I saw your comment – wich Jan 20 '11 at 16:49
1

newlines will make the first part try to execute and fail with a command not found error use var=$(cat file | tr -d '\n') to remove all new lines, including any trailing ones – Jonathan Jul 05 '17 at 10:51
@Jonathan no it won't – wich Jul 05 '17 at 14:46
Be careful when using this with a single-line file. The resulting *array* variable will look like a normal one, but you won't be able to easily export it: `echo X > f; mapfile -t V < f; echo V is $V; export V; env | grep V=`. Note how `V` is missing from `env` despite being defined before exporting. – bers Feb 13 '23 at 08:18

score 55 · Answer 2 · edited Dec 27 '18 at 00:35

55

The simplest way is probably:

var=$(< file)

which doesn't create a new process.

edited Dec 27 '18 at 00:35

nbro

answered Jan 20 '11 at 16:48

3

This works in Bash and other advanced shells, but not in the Bourne shell. – Dennis Williamson Jan 20 '11 at 18:31
4

not cross platform... won't work in sh see http://stackoverflow.com/questions/7427262/how-to-read-a-file-into-a-variable-in-shell – Amos Folarin Jun 26 '15 at 17:38
1

Does anyone/anything even still use non-bash sh in 2018? Maybe Dick Tracy's watch?? – David Tonhofer Mar 22 '18 at 17:32
1

Warning: no space prior to the _“<”_ (i.e. _“`(<`”_ instead of _“`( <`”_). – neverMind9 Mar 10 '19 at 13:31
This solution does a transformation over 'endline' char on linux. – Galigator May 31 '21 at 09:58

score 4 · Answer 3 · answered Jan 20 '11 at 16:42

4

var="`cat /path/to/file`"

This is the simple way. Be careful with newlines in the file.

var="`head -1 /path/to/file`"

This will only get the first line and will never include a newline.

answered Jan 20 '11 at 16:42

jamesbtate

1

I have a file nammed "log", and `$x="\`cat log\`"` results in `=2: command not found` – The Student Jan 20 '11 at 16:45

score 4 · Answer 4 · edited May 29 '18 at 19:11

4

I think the easiest way is something like

$ myvar=`cat file`

edited May 29 '18 at 19:11

AlikElzin-kilaka

answered Jan 20 '11 at 16:46

giles123

4

It's not necessary to export the variable and the spaces around the equal sign won't work. – Dennis Williamson Jan 20 '11 at 18:29

score 1 · Answer 5 · answered Jan 20 '11 at 16:43

1

I think it will strip newlines, but here it is anyway:

variable=$(cat filename)

answered Jan 20 '11 at 16:43

orlp

9

It will only strip the final newline. If you seem to be getting the other newlines stripped, it's because you're not quoting the variable on output. `echo $variable` vs. `echo "$variable"` – Dennis Williamson Jan 20 '11 at 18:31

5 Answers5