Shell script: get date as variable

Question

I am trying to create a quick script that will get a file from a backup folder. The backup file is generated every day and have the filename format of:

backup-sql-YYYYMMDD.zip

I am trying to get the filename by using:

#!/bin/sh

VAR_1="backup-sql-"
VAR_2=date +%Y%m%d
VAR_3=$VAR_1$VAR_2

echo "$VAR_3"

However the output is:

backup-sql-

When I run:

date +%Y%m%d

I get

20180704

So I am not sure why this is happening. Please can someone help me :)

You are missing command substitution. Paste your code to [shellcheck.net](https://www.shellcheck.net/). — PesaThe, Jul 04 '18 at 10:33
Your shell must be broken since it's not giving you a syntax error on `VAR_2=date +%Y%m%d` (assuming you'd have acted on it or at the very least told us about it if you were getting a syntax error). — Ed Morton, Jul 04 '18 at 12:23
@EdMorton Thanks for the reply, I solved it with the answer below by adding `$()` — modusTollens, Jul 04 '18 at 13:08
Possible duplicate of [How to set a variable to the output of a command in Bash?](https://stackoverflow.com/questions/4651437/how-to-set-a-variable-to-the-output-of-a-command-in-bash) — Benjamin W., Jul 04 '18 at 13:27

score 1 · Answer 1 · answered Jul 04 '18 at 10:35

1

You should be using backticks to capture the output of the date command and assign it to a shell variable.

VAR2=`date "+%Y%m%d"`

In case you want to make sure the variable value is passed on to subsequent child processes you may want to export it as:

export VAR2=`date "+%Y%m%d"`

answered Jul 04 '18 at 10:35

asatsi

452
2
5

No you should not be using backticks. See https://www.gnu.org/software/bash/manual/html_node/Command-Substitution.html – Ed Morton Jul 04 '18 at 12:24

score 1 · Accepted Answer · answered Jul 04 '18 at 11:40

You could use:

$(command)

or

`command`

From your example give a try to:

VAR_2=$(date +%Y%m%d)

Check Command Substitution for more details:

When the old-style backquote form of substitution is used, backslash retains its literal meaning except when followed by ‘$’, ‘`’, or ‘\’. The first backquote not preceded by a backslash terminates the command substitution. When using the $(command) form, all characters between the parentheses make up the command; none are treated specially.

Shell script: get date as variable

2 Answers2