How to use Linux shell echo date to a log file All In One

How to use Linux shell echo date to a log file All In One

如何使用 Linux shell 将日期打印输出到日志文件

solutions

1. date

# 命令 ✅
$ date >> /etc/rc.local.md

# echo 反斜号 ✅
$ echo `date` >> /etc/rc.local.md

# echo 双引号 包裹 反斜号 ✅
$ echo "`date` \n"  >> /etc/rc.local.md

eric@rpi3b:~ $ sudo /etc/rc.local
My IP address is 192.168.101.17 
eric@rpi3b:~ $ cat /etc/rc.local.md
# rc.local logs md file

# timestamp 时间戳

Tue Mar 11 01:16:53 CST 2025 

/etc/rc.local testing begin ✅
/etc/rc.local testing end ✅
eric@rpi3b:~ $ cat /etc/rc.local
#!/bin/sh -e

# 添加日期时间
echo "`date` \n" >> /etc/rc.local.md 2>&1

echo "/etc/rc.local testing begin ✅" >> /etc/rc.local.md 2>&1


# add below line before exit 0 ✅
# Print the IP address
_IP=$(hostname -I) || true
if [ "$_IP" ]; then
  printf "My IP address is %s\n" "$_IP"
fi

# 禁用电源关闭
iwconfig wlan0 power off


echo "/etc/rc.local testing end ✅" >> /etc/rc.local.md 2>&1

# sudo /sbin/iw dev wlan0 set power_save off
# su eric -c "exec /sbin/iw dev wlan0 set power_save off"

# 可执行脚本
# su eric -c "exec /home/eric/Desktop/echo-test.sh"


exit 0

2. 使用 local env variable 环境变量

$(command)

eric@rpi3b:~ $ DATE
-bash: DATE: command not found
eric@rpi3b:~ $ date
Tue Mar 11 01:23:14 CST 2025
# ❌
eric@rpi3b:~ $ DATE=date 
eric@rpi3b:~ $ echo "$DATE \n"
date \n
# $(command) ✅
eric@rpi3b:~ $ DATE=$(date)
eric@rpi3b:~ $ echo "$DATE \n"
Tue Mar 11 01:24:16 CST 2025 \n

command

# `command` ✅
eric@rpi3b:~ $ DATE=`date`
eric@rpi3b:~ $ echo "$DATE \n"
Tue Mar 11 01:28:19 CST 2025 \n

demos

# 命令 ✅
➜  cyclic-express-server git:(main) ✗ $ date
Tue Mar 11 01:01:15 CST 2025
# echo 反斜号 ✅
➜  cyclic-express-server git:(main) ✗ $ echo `date`
Tue Mar 11 01:05:07 CST 2025
# echo 双引号 包裹 反斜号 ✅
➜  cyclic-express-server git:(main) ✗ $ echo "`date` \n"
Tue Mar 11 01:04:07 CST 2025 



# ehco $var ❌
➜  cyclic-express-server git:(main) ✗ $ echo "$date \n"

# ehco 双引号 包裹 string ❌
➜  cyclic-express-server git:(main) ✗ $ echo "date \n"
date

# echo 单引号 包裹 反斜号 ❌
➜  cyclic-express-server git:(main) ✗ $ echo '`date` \n'
`date` 

# echo string ❌
➜  cyclic-express-server git:(main) ✗ $ echo date
date

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refs

https://unix.stackexchange.com/questions/98391/what-is-the-difference-between-echo-date-echo-date-and-echo-date

https://stackoverflow.com/questions/49770646/how-to-print-current-date-saved-in-a-variable-in-an-echo-sentence-for-shell-scri

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