cronjob 執行時腳本中的 $0 為空

我正在嘗試為 AWS EBS 卷設置自動備份，並使用https://github.com/colinbjohnson/aws-missing-tools/tree/master/ec2-automate-backup來執行此操作。

使用的備份腳本如下（ec2-automate-backup.sh）

#!/bin/bash -
#confirms that executables required for succesful script execution are 
available
prerequisite_check() {
 for prerequisite in basename cut date aws; do
   #use of "hash" chosen as it is a shell builtin and will add programs to hash table, possibly speeding execution. Use of type also considered - open to suggestions.
   hash $prerequisite &> /dev/null
   if [[ $? == 1 ]]; then #has exits with exit status of 70, executable was not found
     echo "In order to use $app_name, the executable \"$prerequisite\" must be installed." 1>&2 ; exit 70
   fi
 done
}

#get_EBS_List gets a list of available EBS instances depending upon the selection_method of EBS selection that is provided by user input
get_EBS_List() {
 case $selection_method in
   volumeid)
     if [[ -z $volumeid ]]; then
       echo "The selection method \"volumeid\" (which is $app_name's default selection_method of operation or requested by using the -s volumeid parameter) requires a volumeid (-v volumeid) for operation. Correct usage is as follows: \"-v vol-6d6a0527\",\"-s volumeid -v vol-6d6a0527\" or \"-v \"vol-6d6a0527 vol-636a0112\"\" if multiple volumes are to be selected." 1>&2 ; exit 64
     fi
     ebs_selection_string="--volume-ids $volumeid"
     ;;
   tag)
     if [[ -z $tag ]]; then
       echo "The selected selection_method \"tag\" (-s tag) requires a valid tag (-t Backup,Values=true) for operation. Correct usage is as follows: \"-s tag -t Backup,Values=true.\"" 1>&2 ; exit 64
     fi
     ebs_selection_string="--filters Name=tag:$tag"
     ;;
   *) echo "If you specify a selection_method (-s selection_method) for selecting EBS volumes you must select either \"volumeid\" (-s volumeid) or \"tag\" (-s tag)." 1>&2 ; exit 64 ;;
 esac
 #creates a list of all ebs volumes that match the selection string from above
 ebs_backup_list=$(aws ec2 describe-volumes --region $region $ebs_selection_string --output text --query 'Volumes[*].VolumeId')
 #takes the output of the previous command 
 ebs_backup_list_result=$(echo $?)
 if [[ $ebs_backup_list_result -gt 0 ]]; then
   echo -e "An error occurred when running ec2-describe-volumes. The error returned is below:\n$ebs_backup_list_complete" 1>&2 ; exit 70
 fi
}

create_EBS_Snapshot_Tags() {
 #snapshot tags holds all tags that need to be applied to a given snapshot - by aggregating tags we ensure that ec2-create-tags is called only onece
 snapshot_tags="Key=CreatedBy,Value=ec2-automate-backup"
 #if $name_tag_create is true then append ec2ab_${ebs_selected}_$current_date to the variable $snapshot_tags
 if $name_tag_create; then
   snapshot_tags="$snapshot_tags Key=Name,Value=ec2ab_${ebs_selected}_$current_date"
 fi
 #if $hostname_tag_create is true then append --tag InitiatingHost=$(hostname -f) to the variable $snapshot_tags
 if $hostname_tag_create; then
   snapshot_tags="$snapshot_tags Key=InitiatingHost,Value='$(hostname -s)'"
 fi
 #if $purge_after_date_fe is true, then append $purge_after_date_fe to the variable $snapshot_tags
 if [[ -n $purge_after_date_fe ]]; then
   snapshot_tags="$snapshot_tags Key=PurgeAfterFE,Value=$purge_after_date_fe Key=PurgeAllow,Value=true"
 fi
 #if $user_tags is true, then append Volume=$ebs_selected and Created=$current_date to the variable $snapshot_tags
 if $user_tags; then
   snapshot_tags="$snapshot_tags Key=Volume,Value=${ebs_selected} Key=Created,Value=$current_date"
 fi
 #if $snapshot_tags is not zero length then set the tag on the snapshot using aws ec2 create-tags
 if [[ -n $snapshot_tags ]]; then
   echo "Tagging Snapshot $ec2_snapshot_resource_id with the following Tags: $snapshot_tags"
   tags_argument="--tags $snapshot_tags"
   aws_ec2_create_tag_result=$(aws ec2 create-tags --resources $ec2_snapshot_resource_id --region $region $tags_argument --output text 2>&1)
 fi
}

get_date_binary() {
 #$(uname -o) (operating system) would be ideal, but OS X / Darwin does not support to -o option
 #$(uname) on OS X defaults to $(uname -s) and $(uname) on GNU/Linux defaults to $(uname -s)
 uname_result=$(uname)
 case $uname_result in
   Darwin) date_binary="posix" ;;
   FreeBSD) date_binary="posix" ;;
   Linux) date_binary="linux-gnu" ;;
   *) date_binary="unknown" ;;
 esac
}

get_purge_after_date_fe() {
case $purge_after_input in
 #any number of numbers followed by a letter "d" or "days" multiplied by 86400 (number of seconds in a day)
 [0-9]*d) purge_after_value_seconds=$(( ${purge_after_input%?} * 86400 )) ;;
 #any number of numbers followed by a letter "h" or "hours" multiplied by 3600 (number of seconds in an hour)
 [0-9]*h) purge_after_value_seconds=$(( ${purge_after_input%?} * 3600 )) ;;
 #any number of numbers followed by a letter "m" or "minutes" multiplied by 60 (number of seconds in a minute)
 [0-9]*m) purge_after_value_seconds=$(( ${purge_after_input%?} * 60 ));;
 #no trailing digits default is days - multiply by 86400 (number of minutes in a day)
 *) purge_after_value_seconds=$(( $purge_after_input * 86400 ));;
esac
#based on the date_binary variable, the case statement below will determine the method to use to determine "purge_after_days" in the future
case $date_binary in
 linux-gnu) echo $(date -d +${purge_after_value_seconds}sec -u +%s) ;;
 posix) echo $(date -v +${purge_after_value_seconds}S -u +%s) ;;
 *) echo $(date -d +${purge_after_value_seconds}sec -u +%s) ;;
esac
}

purge_EBS_Snapshots() {
 # snapshot_purge_allowed is a string containing the SnapshotIDs of snapshots
 # that contain a tag with the key value/pair PurgeAllow=true
 snapshot_purge_allowed=$(aws ec2 describe-snapshots --region $region --filters Name=tag:PurgeAllow,Values=true --output text --query 'Snapshots[*].SnapshotId')

 for snapshot_id_evaluated in $snapshot_purge_allowed; do
   #gets the "PurgeAfterFE" date which is in UTC with UNIX Time format (or xxxxxxxxxx / %s)
   purge_after_fe=$(aws ec2 describe-snapshots --region $region --snapshot-ids $snapshot_id_evaluated --output text | grep ^TAGS.*PurgeAfterFE | cut -f 3)
   #if purge_after_date is not set then we have a problem. Need to alert user.
   if [[ -z $purge_after_fe ]]; then
     #Alerts user to the fact that a Snapshot was found with PurgeAllow=true but with no PurgeAfterFE date.
     echo "Snapshot with the Snapshot ID \"$snapshot_id_evaluated\" has the tag \"PurgeAllow=true\" but does not have a \"PurgeAfterFE=xxxxxxxxxx\" key/value pair. $app_name is unable to determine if $snapshot_id_evaluated should be purged." 1>&2
   else
     # if $purge_after_fe is less than $current_date then
     # PurgeAfterFE is earlier than the current date
     # and the snapshot can be safely purged
     if [[ $purge_after_fe < $current_date ]]; then
       echo "Snapshot \"$snapshot_id_evaluated\" with the PurgeAfterFE date of \"$purge_after_fe\" will be deleted."
       aws_ec2_delete_snapshot_result=$(aws ec2 delete-snapshot --region $region --snapshot-id $snapshot_id_evaluated --output text 2>&1)
     fi
   fi
 done
}

#calls prerequisitecheck function to ensure that all executables required for script execution are available
prerequisite_check

app_name=$(basename $0)
#sets defaults
selection_method="volumeid"
#date_binary allows a user to set the "date" binary that is installed on their system and, therefore, the options that will be given to the date binary to perform date calculations
date_binary=""
#sets the "Name" tag set for a snapshot to false - using "Name" requires that ec2-create-tags be called in addition to ec2-create-snapshot
name_tag_create=false
#sets the "InitiatingHost" tag set for a snapshot to false
hostname_tag_create=false
#sets the user_tags feature to false - user_tag creates tags on snapshots - by default each snapshot is tagged with volume_id and current_date timestamp
user_tags=false
#sets the Purge Snapshot feature to false - if purge_snapshots=true then snapshots will be purged
purge_snapshots=false
#handles options processing

while getopts :s:c:r:v:t:k:pnhu opt; do
 case $opt in
   s) selection_method="$OPTARG" ;;
   c) cron_primer="$OPTARG" ;;
   r) region="$OPTARG" ;;
   v) volumeid="$OPTARG" ;;
   t) tag="$OPTARG" ;;
   k) purge_after_input="$OPTARG" ;;
   n) name_tag_create=true ;;
   h) hostname_tag_create=true ;;
   p) purge_snapshots=true ;;
   u) user_tags=true ;;
   *) echo "Error with Options Input. Cause of failure is most likely that an unsupported parameter was passed or a parameter was passed without a corresponding option." 1>&2 ; exit 64 ;;
 esac
done

#sources "cron_primer" file for running under cron or other restricted environments - this file should contain the variables and environment configuration required for ec2-automate-backup to run correctly
if [[ -n $cron_primer ]]; then
 if [[ -f $cron_primer ]]; then
   source $cron_primer
 else
   echo "Cron Primer File \"$cron_primer\" Could Not Be Found." 1>&2 ; exit 70
 fi
fi

#if region is not set then:
if [[ -z $region ]]; then
 #if the environment variable $EC2_REGION is not set set to us-east-1
 if [[ -z $EC2_REGION ]]; then
   region="us-east-1"
 else
   region=$EC2_REGION
 fi
fi

#sets date variable
current_date=$(date -u +%s)

#sets the PurgeAfterFE tag to the number of seconds that a snapshot should be retained
if [[ -n $purge_after_input ]]; then
 #if the date_binary is not set, call the get_date_binary function
 if [[ -z $date_binary ]]; then
   get_date_binary
 fi
 purge_after_date_fe=$(get_purge_after_date_fe)
 echo "Snapshots taken by $app_name will be eligible for purging after the following date (the purge after date given in seconds from epoch): $purge_after_date_fe."
fi

#get_EBS_List gets a list of EBS instances for which a snapshot is desired. The list of EBS instances depends upon the selection_method that is provided by user input
get_EBS_List

#the loop below is called once for each volume in $ebs_backup_list - the currently selected EBS volume is passed in as "ebs_selected"
for ebs_selected in $ebs_backup_list; do
 ec2_snapshot_description="ec2ab_${ebs_selected}_$current_date"
 ec2_snapshot_resource_id=$(aws ec2 create-snapshot --region $region --description $ec2_snapshot_description --volume-id $ebs_selected --output text --query SnapshotId 2>&1)
 if [[ $? != 0 ]]; then
   echo -e "An error occurred when running ec2-create-snapshot. The error returned is below:\n$ec2_create_snapshot_result" 1>&2 ; exit 70
 fi  
 create_EBS_Snapshot_Tags
done

#if purge_snapshots is true, then run purge_EBS_Snapshots function
if $purge_snapshots; then
 echo "Snapshot Purging is Starting Now."
 purge_EBS_Snapshots
fi

使用的 cron Prime 文件如下（cron-primer.sh）

#!/bin/bash -
# EC2_HOME required for EC2 API Tools
export EC2_HOME=/usr/local/ec2/apitools
# JAVA_HOME required for EC2 API Tools
export JAVA_HOME=/usr/lib/jvm/java-7-openjdk-amd64/
# export PATH=/bin is required for cut, date, grep
# export PATH=/opt/aws/bin/ is required for EC2 API Tools
export PATH=/usr/local/bin:/bin:/usr/bin:/usr/local/sbin:/usr/sbin:/sbin:/usr/local/ec2/apitools/bin/
export AWS_ACCESS_KEY=XXXXXX
export AWS_SECRET_KEY=XXXXXX
# The environmental variable names seem to have changed
export AWS_ACCESS_KEY_ID=XXXXXX
export AWS_SECRET_ACCESS_KEY=XXXXXX

（請注意，唯一需要的環境變數是 AWS_ACCESS_KEY_ID 和 AWS_SECRET_ACCESS_KEY，但我留下了其他變數，因為它們已被舊的 EC2 CLI 實施使用）

直接從控制台執行此操作時，該腳本執行完美，但是當我從 cronjob 執行該腳本時，它不起作用。通過電子郵件發送以下錯誤：

In order to use , the executable "aws" must be installed.

請注意，此錯誤來自腳本的第 8 行。該消息推斷無法找到 aws 執行檔，但 /usr/local/bin 中有一個符號連結指向該文件，該文件包含在 PATH 變數中。此外，人們可以看到， $ 0 variable ( $ app_name) 似乎是空的，因為它沒有列印。（在我正確安裝 AWS CLI 之前從控制台執行時，同樣的錯誤列印正確，所以我知道腳本本身沒有錯誤）

crontab 如下所示：

8 * * * * /usr/local/ec2/scripts/ec2-automate-backup.sh -r eu-west-1 -s tag -t "Backup,Values=true" -k 7 -p -n -c /usr/local/ec2/scripts/cron-primer.sh

另外，我想將腳本的結果輸出到文件中，為此我將 cronjob 設置為

8 * * * * /usr/local/ec2/scripts/ec2-automate-backup.sh -r eu-west-1 -s tag -t "Backup,Values=true" -k 1 -p -n -c /usr/local/ec2/scripts/cron-primer.sh &> /var/log/ebs_backup/ec2-automate-backup_`date +"%Y%m%d"`.log

哪個沒有創建文件，如果有人可以突出顯示未創建文件的原因（目標文件夾中的權限是正確的），將不勝感激

函式prerequisite_check定義說，basename, cut, date命令aws應該可用。

從 執行時腳本無法找到aws命令crontab。因此，您遇到了錯誤。

在crontab中，您需要修改 PATH 變數以包含path可執行aws文件，方法是將它們寫在您的cron行之前。

您可以使用以下語法path在crontab.

~]$ crontab -l
PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin
50 1 * * * sh /home/user/mybackupjob.sh

似乎問題已與該行有關

prerequisite_check

在設置所有變數之前放置的腳本中。我將檢查移至 cron 引物連結的點下方，一切正常。奇怪的是，一個如此常用的腳本有這樣的錯誤卻沒有人報告。我認為該錯誤已在最近的更新中引入

簡而言之，所描述的症狀與未設置的 PATH 變數有關，未設置的原因是使用的腳本中的錯誤。

引用自：https://serverfault.com/questions/753958