preserve variable within bash script

Question

I have a bash script I am using to deploy updates automatically. It also includes logs of when the updates have been run. I have added the entire bash script below. The issue I am having is within the output file (/my-cron-file/script/update-me.sh)

This is the output I am getting:

!/bin/bash
apt update > /my-cron-files/update-logs/'2025-03-26_16:24.53'.log

what i want the output to be:

!/bin/bash
apt update > /my-cron-files/update-logs/'$(date '+%Y-%m-%d_%H:%M.%S')'.log

Here is my bash script:

#!/bin/bash
mkdir /my-cron-files
mkdir /my-cron-files/update-logs
mkdir /my-cron-files/upgrade-logs
mkdir /my-cron-files/reboot-logs
mkdir /my-cron-files/scripts


LOG_DATE=$(date '+%Y-%m-%d_%H:%M.%S')
CRON_SCHEDULE_1="0 1 * * *"
CRON_SCRIPT_1="/my-cron-files/scripts/update-me.sh"
CRON_JOB_1="$CRON_SCHEDULE_1 $CRON_SCRIPT_1"
CRON_SCHEDULE_2="0 2 * * *"
CRON_SCRIPT_2="/my-cron-files/scripts/upgrade-me.sh"
CRON_JOB_2="$CRON_SCHEDULE_2 $CRON_SCRIPT_2"
CRON_SCHEDULE_3="0 3 * * *"
CRON_SCRIPT_3="/my-cron-files/scripts/reboot-me.sh >> /my-cron-files/reboot-logs/reboot.log"
CRON_JOB_3="$CRON_SCHEDULE_3 $CRON_SCRIPT_3"

(crontab -l ; echo "$CRON_JOB_1") | crontab
(crontab -l ; echo "$CRON_JOB_2") | crontab
(crontab -l ; echo "$CRON_JOB_3") | crontab


# Script to create another executable script

# Define the content of the new script
UPDATE_SCRIPT="
#!/bin/bash
apt update > /my-cron-files/update-logs/'$LOG_DATE'.log
"

UPGRADE_SCRIPT="
#!/bin/bash
apt upgrade -y > /my-cron-files/upgrade-logs/$LOG_DATE.log
"

REBOOT_SCRIPT="
#!/bin/bash
if [ -f /var/run/reboot-required ]; then
echo "$LOG_DATE", 'reboot required'
reboot
else
echo "$LOG_DATE", 'reboot not rquired'
fi
"


# Define the name of the new script
UPDATE_SCRIPT_NAME="update-me.sh"
UPGRADE_SCRIPT_NAME="upgrade-me.sh"
REBOOT_SCRIPT_NAME="reboot-me.sh"

# Create the new script file
echo "$UPDATE_SCRIPT" > /my-cron-files/scripts/"$UPDATE_SCRIPT_NAME"
echo "$UPGRADE_SCRIPT" > /my-cron-files/scripts/"$UPGRADE_SCRIPT_NAME"
echo "$REBOOT_SCRIPT" > /my-cron-files/scripts/"$REBOOT_SCRIPT_NAME"

# Make the new script executable
chmod +x /my-cron-files/scripts/"$UPDATE_SCRIPT_NAME"
chmod +x /my-cron-files/scripts/"$UPGRADE_SCRIPT_NAME"
chmod +x /my-cron-files/scripts/"$REBOOT_SCRIPT_NAME"

echo "Scripts '$UPDATE_SCRIPT_NAME', '$UPGRADE_SCRIPT_NAME', and '$REBOOT_SCRIPT_NAME' has been created and made executable."

woodenadmin · Accepted Answer · 2025-03-26 20:59:53Z

0

Use backslashes (\) to escape characters with special meaning (including backslashes themselves).

So, replace

LOG_DATE=$(date '+%Y-%m-%d_%H:%M.%S')

with:

LOG_DATE=$\(date\ \'+%Y-%m-%d_%H:%M.%S\'\)

edited Mar 26, 2025 at 20:59

answered Mar 26, 2025 at 20:55

woodenadmin

2042 silver badges21 bronze badges

Add a comment |

Ed Morton · Accepted Answer · 2025-06-16 10:50:12Z

Use the appropriate quotes (see https://mywiki.wooledge.org/Quotes). Instead of what you have:

$ LOG_DATE=$(date '+%Y-%m-%d_%H:%M.%S')
$ echo "$LOG_DATE"
2025-06-16_05:41.42

just quote the right side of the assignment to stop the shell from interpreting it at that time:

$ LOG_DATE='$(date "+%Y-%m-%d_%H:%M.%S")'
$ echo "$LOG_DATE"
$(date "+%Y-%m-%d_%H:%M.%S")

or if you prefer:

$ LOG_DATE='$(date '\''+%Y-%m-%d_%H:%M.%S'\'')'
$ echo "$LOG_DATE"
$(date '+%Y-%m-%d_%H:%M.%S')

Please also read correct-bash-and-shell-script-variable-capitalization and then fix your variable names.

Also, copy/paste your script into http://shellcheck.net and it'll tell you about bugs like this one:

REBOOT_SCRIPT="
#!/bin/bash
if [ -f /var/run/reboot-required ]; then
echo "$LOG_DATE", 'reboot required'
reboot
else
echo "$LOG_DATE", 'reboot not rquired'
fi

where you have REBOOT_SCRIPT="..."$LOG_DATE"...", i.e. you're using "s inside a "-quoted string and so the quotes around "$LOG_DATE" are actually unquoting it and thereby leaving it open to the shell to interpret for globbing, etc.

Finally - typo, rquired vs required.

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