需要定义一个名为failed的bash变量,并将值设置为False。当从cron作业调用我们的脚本时,特定的任务可能会失败,然后我需要将failed转换为True。基于$failed,我需要发送一封电子邮件警告我的cron作业失败了。那么,如何在Linux服务器上运行的shell脚本中声明和使用布尔变量呢?
Bash中没有布尔值。但是,我们可以根据需要将shell变量的值定义为0(“False”)或1(“True”)。不过,Bash也支持布尔表达式条件。让我们看看如何在Bash中组合这两个概念来声明布尔变量,并在运行在Linux、macOS、FreeBSD或类unix系统上的shell脚本中使用它们。
在bash中声明布尔变量
语法如下,定义如下内容
failed=0 # False
jobdone=1 # True
## 更具可读性的语法 ##
failed=false
jobdone=true
现在,当$failed是数字(例如0或1)时,我们可以按以下方式检查它:
if [ $failed -eq 1 ]thenecho "Job failed"elseecho "Job done"fi
就这样。
如何在Shell脚本中声明和使用布尔变量(例如“ true”和“ false”)
当然,我们可以将它们定义为字符串,并使我们的代码更具可读性:
#!/bin/bash# Declare it as string failed="false" if [ "$failed" == "true" ]thenecho "Job failed"elseecho "Job done"fi
或者
# set it to trueemail_sent=true# ...do your stuff and flip email_sent to 'false' if needed ...if [ "$email_sent" = true ] thenecho 'Data logged and email sent too.'elseecho 'ALERT: Operation failed.'logger 'ALERT: Operation failed.'fi
在bash下定义布尔变量的替代语法如下:
# Set this one to true jobstatus=true # Check it if [ "$jobstatus" = true ] ; then echo 'Okay :)' else echo 'Noop :(' fi # Double bracket format syntax to test Boolean variables in bash bool=false if [[ "$bool" = true ]] ; then echo 'Done.' else echo 'Failed.' fi# Let us Declare Two Boolean Variables
让我们对其进行测试:
shell脚本示例中的Bash布尔变量
下面是一个示例脚本:
#!/bin/bash# Purpose: Backup stuff from /data/apps# Tested on : AWS EC2 with EFS and Ubuntu 20.04 Pro servers# ---------------------------------------------------------source "/apps/.keychain/$HOSTNAME-sh"source "/apps/scripts/cli_app.sh"# Set failed to 'False' failed=0 D="/nfsefs/ec2mum/prodwwwroot"log="/tmp/server.log.$$.txt"# Log everything to our fileexec 3>&1 4>&2trap 'exec 2>&4 1>&3' 0 1 2 3exec 1>"${log}" 2>&1# Backup all web serversfor s in www-0{1..8}do/usr/bin/rsync -az --delete backupt@${s}:/data/apps/ ${D}/${s}/# set to 'true' when rsync failed and continue loop [ $? -ne 0 ] && failed=1done# See if rsync failed in loop if [ $failed -eq 1 ]thenecho "$0 script error: rsync backup failed. See attached log file." | mail -A ${log} -s "$HOSTNAME - LXD backup failed" -r sysuser@my-corp-tld alert@somewhere-tldpush_to_mobile "$0" "Dear sysadmin,Backup failed at $HOSTNAME at $(date). ---- log:start ---$(<${log})--- log:end ---- Yours faithfully,$0"fi[ -f "${log}" ] && rm -f "${log}"
Bash布尔测试
首先,定义一个日志文件:
log="/tmp/rsnapshot.$$.txt"
让我们运行rsnapshot命令:
/usr/bin/rsnapshot "$1" 2>&1 | $HOME/bin/error-scanner.pl > "${log}"
在$status中获取bash命令的退出状态,如下所示:
status=$?
接下来在我们的$log文件中搜索ERROR:
alogs="$(egrep -w '^ERROR:|ERROR' $log)"
如果$status不为零(命令失败)或$alogs不为空(由$HOME/bin/error-scanner.pl报告错误),那么通过电子邮件/文本消息通知系统管理员或开发人员:
if [ $status -ne 0 ] || [ "$alogs" != "" ]; thensub="Backup job failed at $HOSTNAME"mail -A "$log" -s "$sub" -r sys@somewhere-tld sysadmin@gmail-tld <<< "$0 script ended with errors when we ran /usr/bin/rsnapshot \"$1\" $alogs"push_to_mobile "$0" "$sub$0 script ended with errors when we ran /usr/bin/rsnapshot \"$1\"$alogsSee email for detailed log."elsesub="Backup successful at $HOSTNAME"#push_to_mobile "$0" "$sub. See email for detailed backup log." >/dev/null#mail -A "$log" -s "$sub" -r sys@somewhere-tld sysadmin@gmail-tld <<< "$0 /usr/bin/rsnapshot ran successfully\"$1\" $alogs"fi
最后,删除$log文件:
[ -f "$log" ] && rm -f "$log"
总结
本文我们讲解了如何在Linux或类Unix系统的shell脚本/bash中声明和使用布尔变量。使用man命令查看以下手册页:
$ man bash
$ help test
$ help if