如何在bash脚本的两次连续运行之间存储状态

Question

我有一个bash脚本，它每分钟使用一个cron作业运行一次。我想保存脚本的状态，以便在下次运行时重用。

保存状态的最佳方式是什么(在这种情况下是一个分配了数字的变量(；因此，在下一次运行中，可以将数字与以前运行的值进行比较。

Answer 1

从文件保存和重新加载变量值的示例

#!/usr/bin/env bash
# The file holding persistent variable value
statefile='/var/statefile'
# Declare our variable as holding an integer
declare -i persistent_counter
# If the persistence file exists, read the variable value from it
if [ -f "$statefile" ]; then
read -r persistent_counter <"$statefile"
else
persistent_counter=0
fi
# Update counter
persistent_counter="$((persistent_counter + 1))"
# Save value to file
printf '%dn' "$persistent_counter" >"$statefile"

另一种采购方式：

#!/usr/bin/env bash
# The file holding persistent variable value
statefile='/var/statefile'
# Source the statefile
. "$statefile" 2>/dev/null || :
# Declare our variable as holding an integer
declare -i persistent_counter
# Assign default value if unset
: ${persistent_counter:=0}
# Update counter
persistent_counter="$((persistent_counter + 1))"
# Persist variable to file
declare -p persistent_counter >"$statefile"

持久化多个变量(一个整数、一个字符串和一个数组(：

#!/usr/bin/env bash
# The file holding persistent variable value
statefile='/tmp/statefile'
# Initialize variables even if they are later state restored
persistent_counter=0
persistent_last_date="never"
persistent_array=()
save_state () {
typeset -p "$@" >"$statefile"
}
# Source the statefile to restore state
. "$statefile" 2>/dev/null || :
# Set save_state call on script exit to automatically persist state
trap 'save_state persistent_counter persistent_last_date persistent_array' EXIT
# Display restored variables
printf 'Last time script ran was: %sn' "$persistent_last_date"
printf 'Counter was: %dn' "$persistent_counter"
printf 'Array contained %d elements:n' "${#persistent_array[@]}"
printf '%sn' "${persistent_array[@]}"
# Update counter
persistent_counter="$((persistent_counter + 1))"
# Update Array
if ! [ "$persistent_last_date" = 'never' ]; then
persistent_array+=("$persistent_last_date")
fi
# Update last run time
persistent_last_date="$(date -R)"
# Now that the script exit, it will automatically trap call save_state