我想执行一个脚本并让它每 x 分钟运行一个命令。
此外，关于学习 bash 脚本的任何资源的任何一般性建议都非常酷。我将 Linux 用于我的个人开发工作，因此 bash 脚本对我来说并不完全陌生，我只是没有从头开始编写任何自己的脚本。
【问题讨论】：
cron了吗？
标签： bash
如果要定期运行命令，有 3 种方式：
crontab 命令例如。 * * * * * command（每分钟运行一次）while true; do ./my_script.sh; sleep 60; done（不精确）见cron
一些关于最佳 bash 脚本实践的建议：
http://mywiki.wooledge.org/BashFAQ
导游：http://mywiki.wooledge.org/BashGuide
参考：http://www.gnu.org/software/bash/manual/bash.html
http://wiki.bash-hackers.org/
使用更多报价！：http://www.grymoire.com/Unix/Quote.html
脚本等：http://www.shelldorado.com/
【讨论】：
这是我减少循环负载运行时间漂移的解决方案。
tpid=0
while true; do
wait ${tpid}
sleep 3 & tpid=$!
{ body...; }
done
定时器对象方法有一些近似，睡眠命令与所有其他命令并行执行，甚至包括条件检查中的 true。我认为它是最精确的变体，没有使用 date 命令的漂移计数。
可能有真正的计时器对象 bash 函数，仅通过 'echo' 调用实现计时器事件，然后使用 read cmd 管道循环，如下所示：
timer | { while read ev; do...; done; }
【讨论】：
macOS 用户：这是 的 GNU watch 命令（截至版本 0.3.0）的部分实现主要用于视觉检查的交互式定期调用：
它与 GNU 版本的语法兼容，如果使用了未实现的功能，则会失败并显示特定的错误消息。
显着限制：
--color）。还实现了一些非标准功能，例如等待 成功 (-E) 以补充等待错误 (-e) 并将最后一次调用的时间显示为以及到目前为止经过的总时间。
运行watch -h了解详情。
例子：
watch -n 1 ls # list current dir every second
watch -e 'ls *.lockfile' # list lock files and exit once none exist anymore.
源代码（粘贴到名为watch 的脚本文件中，使其可执行，然后放在$PATH 的目录中；注意此处的语法高亮显示已损坏，但代码有效):
#!/usr/bin/env bash
THIS_NAME=$(basename "$BASH_SOURCE")
VERSION='0.1'
# Helper function for exiting with error message due to runtime error.
# die [errMsg [exitCode]]
# Default error message states context and indicates that execution is aborted. Default exit code is 1.
# Prefix for context is always prepended.
# Note: An error message is *always* printed; if you just want to exit with a specific code silently, use `exit n` directly.
die() {
echo "$THIS_NAME: ERROR: ${1:-"ABORTING due to unexpected error."}" 1>&2
exit ${2:-1} # Note: If the argument is non-numeric, the shell prints a warning and uses exit code 255.
}
# Helper function for exiting with error message due to invalid parameters.
# dieSyntax [errMsg]
# Default error message is provided, as is prefix and suffix; exit code is always 2.
dieSyntax() {
echo "$THIS_NAME: PARAMETER ERROR: ${1:-"Invalid parameter(s) specified."} Use -h for help." 1>&2
exit 2
}
# Get the elapsed time since the specified epoch time in format HH:MM:SS.
# Granularity: whole seconds.
# Example:
# tsStart=$(date +'%s')
# ...
# getElapsedTime $tsStart
getElapsedTime() {
date -j -u -f '%s' $(( $(date +'%s') - $1 )) +'%H:%M:%S'
}
# Command-line help.
if [[ "$1" == '--help' || "$1" == '-h' ]]; then
cat <<EOF
SYNOPSIS
$THIS_NAME [-n seconds] [opts] cmd [arg ...]
DESCRIPTION
Executes a command periodically and displays its output for visual inspection.
NOTE: This is a PARTIAL implementation of the GNU \`watch\` command, for OS X.
Notably, the output is not limited to one screenful, and displaying
output differences and using precise timing are not supported.
Also, colored output is always passed through (--color is implied).
Unimplemented features are marked as [NOT IMPLEMENTED] below.
Conversely, features specific to this implementation are marked as [NONSTD].
Reference version is GNU watch 0.3.0.
CMD may be a simple command with separately specified
arguments, if any, or a single string containing one or more
;-separated commands (including arguments) - in the former case the command
is directly executed by bash, in the latter the string is passed to \`bash -c\`.
Note that GNU watch uses sh, not bash.
To use \`exec\` instead, specify -x (see below).
By default, CMD is re-invoked indefinitely; terminate with ^-C or
exit based on conditions:
-e, --errexit
exits once CMD indicates an error, i.e., returns a non-zero exit code.
-E, --okexit [NONSTD]
is the inverse of -e: runs until CMD returns exit code 0.
By default, all output is passed through; the following options modify this
behavior; note that suppressing output only relates to CMD's output, not the
messages output by this utility itself:
-q, --quiet [NONSTD]
suppresses stdout output from the command invoked;
-Q, --quiet-both [NONSTD]
suppresses both stdout and stderr output.
-l, --list [NONSTD]
list-style display; i.e., suppresses clearing of the screen
before every invocation of CMD.
-n secs, --interval secs
interval in seconds between the end of the previous invocation of CMD
and the next invocation - 2 seconds by default, fractional values permitted;
thus, the interval between successive invocations is the specified interval
*plus* the last CMD's invocation's execution duration.
-x, --exec
uses \`exec\` rather than bash to execute CMD; this requires
arguments to be passed to CMD to be specified as separate arguments
to this utility and prevents any shell expansions of these arguments
at invocation time.
-t, --no-title
suppresses the default title (header) that displays the interval,
and (NONSTD) a time stamp, the time elapsed so far, and the command executed.
-b, --beep
beeps on error (bell signal), i.e., when CMD reports a non-zero exit code.
-c, --color
IMPLIED AND ALWAYS ON: colored command output is invariably passed through.
-p, --precise [NOT IMPLEMENTED]
-d, --difference [NOT IMPLEMENTED]
EXAMPLES
# List files in home folder every second.
$THIS_NAME -n 1 ls ~
# Wait until all *.lockfile files disappear from the current dir, checking every 2 secs.
$THIS_NAME -e 'ls *.lockfile'
EOF
exit 0
fi
# Make sure that we're running on OSX.
[[ $(uname) == 'Darwin' ]] || die "This script is designed to run on OS X only."
# Preprocess parameters: expand compressed options to individual options; e.g., '-ab' to '-a -b'
params=() decompressed=0 argsReached=0
for p in "$@"; do
if [[ $argsReached -eq 0 && $p =~ ^-[a-zA-Z0-9]+$ ]]; then # compressed options?
decompressed=1
params+=(${p:0:2})
for (( i = 2; i < ${#p}; i++ )); do
params+=("-${p:$i:1}")
done
else
(( argsReached && ! decompressed )) && break
[[ $p == '--' || ${p:0:1} != '-' ]] && argsReached=1
params+=("$p")
fi
done
(( decompressed )) && set -- "${params[@]}"; unset params decompressed argsReached p # Replace "$@" with the expanded parameter set.
# Option-parameters loop.
interval=2 # default interval
runUntilFailure=0
runUntilSuccess=0
quietStdOut=0
quietStdOutAndStdErr=0
dontClear=0
noHeader=0
beepOnErr=0
useExec=0
while (( $# )); do
case "$1" in
--) # Explicit end-of-options marker.
shift # Move to next param and proceed with data-parameter analysis below.
break
;;
-p|--precise|-d|--differences|--differences=*)
dieSyntax "Sadly, option $1 is NOT IMPLEMENTED."
;;
-v|--version)
echo "$VERSION"; exit 0
;;
-x|--exec)
useExec=1
;;
-c|--color)
# a no-op: unlike the GNU version, we always - and invariably - pass color codes through.
;;
-b|--beep)
beepOnErr=1
;;
-l|--list)
dontClear=1
;;
-e|--errexit)
runUntilFailure=1
;;
-E|--okexit)
runUntilSuccess=1
;;
-n|--interval)
shift; interval=$1;
errMsg="Please specify a positive number of seconds as the interval."
interval=$(bc <<<"$1") || dieSyntax "$errMsg"
(( 1 == $(bc <<<"$interval > 0") )) || dieSyntax "$errMsg"
[[ $interval == *.* ]] || interval+='.0'
;;
-t|--no-title)
noHeader=1
;;
-q|--quiet)
quietStdOut=1
;;
-Q|--quiet-both)
quietStdOutAndStdErr=1
;;
-?|--?*) # An unrecognized switch.
dieSyntax "Unrecognized option: '$1'. To force interpretation as non-option, precede with '--'."
;;
*) # 1st data parameter reached; proceed with *argument* analysis below.
break
;;
esac
shift
done
# Make sure we have at least a command name
[[ -n "$1" ]] || dieSyntax "Too few parameters specified."
# Suppress output streams, if requested.
# Duplicate stdout and stderr first.
# This allows us to produce output to stdout (>&3) and stderr (>&4) even when suppressed.
exec 3<&1 4<&2
if (( quietStdOutAndStdErr )); then
exec &> /dev/null
elif (( quietStdOut )); then
exec 1> /dev/null
fi
# Set an exit trap to ensure that the duplicated file descriptors are closed.
trap 'exec 3>&- 4>&-' EXIT
# Start loop with periodic invocation.
# Note: We use `eval` so that compound commands - e.g. 'ls; bash --version' - can be passed.
tsStart=$(date +'%s')
while :; do
(( dontClear )) || clear
(( noHeader )) || echo "Every ${interval}s. [$(date +'%H:%M:%S') - elapsed: $(getElapsedTime $tsStart)]: $@"$'\n' >&3
if (( useExec )); then
(exec "$@") # run in *subshell*, otherwise *this* script will be replaced by the process invoked
else
if [[ $* == *' '* ]]; then
# A single argument with interior spaces was provided -> we must use `bash -c` to evaluate it properly.
bash -c "$*"
else
# A command name only or a command name + arguments were specified as separate arguments -> let bash run it directly.
"$@"
fi
fi
ec=$?
(( ec != 0 && beepOnErr )) && printf '\a'
(( ec == 0 && runUntilSuccess )) && { echo $'\n'"[$(date +'%H:%M:%S') - elapsed: $(getElapsedTime $tsStart)] Exiting as requested: exit code 0 reported." >&3; exit 0; }
(( ec != 0 && runUntilFailure )) && { echo $'\n'"[$(date +'%H:%M:%S') - elapsed: $(getElapsedTime $tsStart)] Exiting as requested: non-zero exit code ($ec) reported." >&3; exit 0; }
sleep $interval
done
【讨论】：
除了@sputnick 的回答，还有watch。从手册页：
Execute a program periodically, showing output full screen
默认情况下，这是每 2 秒一次。例如，watch 对于 tailing 日志很有用。
【讨论】：
watch 是非标准的，默认情况下不存在于大多数非 GNU 系统（包括 Mac）上。
避免时间漂移
这是我为消除命令运行所需的时间并仍按计划执行的操作：
#One-liner to execute a command every 600 seconds avoiding time drift
#Runs the command at each multiple of :10 minutes
while sleep $(echo 600-`date "+%s"`%600 | bc); do ls; done
这将漂移不超过一秒钟。然后它将与时钟同步回弹。如果您需要小于 1 秒的漂移并且您的 sleep 命令支持浮点数，请尝试在计算中添加纳秒，如下所示
while sleep $(echo 6-`date "+%s.%N"`%6 | bc); do date '+%FT%T.%N'; done
【讨论】：
echo date 和 bc : t=$SECONDS; while true; do cmd; sleep $(((t+=6) - SECONDS)); done 导致的所有开销。变量SECONDS 是一个bash 内部变量。如果将cmd 替换为date '+%FT%T.%6N'，您可以看到漂移最小
如果您需要直观地监控给出静态输出的命令，请使用watch [options] command。例如，要监控空闲内存，请运行：
watch -n 1 free -m
-n 1 选项将更新间隔设置为 1 秒（默认为 2 秒）。
详情请查看man watch 或online manual。
如果您需要直观地监控日志文件中的更改，tail 是您的首选命令，例如：
tail -f /path/to/logs/file.log
-f（用于“跟随”）选项告诉程序随着文件的增长输出附加的数据。
详情请查看man tail 或online manual。
【讨论】：
我想执行脚本并让它每隔{时间间隔}运行一个命令
cron (https://en.wikipedia.org/wiki/Cron) 就是为此目的而设计的。如果您运行man cron 或man crontab，您将找到有关如何使用它的说明。
关于学习 bash 脚本的任何资源的任何一般性建议都可能非常酷。我将 Linux 用于我的个人开发工作，因此 bash 脚本对我来说并不完全陌生，我只是没有从头开始编写任何自己的脚本。
如果您习惯使用 bash，我建议您先阅读 bash 手册页 (man bash) -- 有很多很酷的花絮。
【讨论】：
我最近面临这个挑战。我想要一种方法，在每 5 分钟在 crontab 上运行的 bash 脚本文件中每小时执行一段脚本，而不必使用睡眠或完全依赖 crontab。如果 TIME_INTERVAL 不满足，脚本将在第一个条件下失败。如果满足 TIME_INTERVAL，但未满足 TIME_CONDITION，则脚本将在第二个条件下失败。下面的脚本确实与 crontab 协同工作 - 相应地进行调整。
注意：touch -m "$0" - 这将改变 bash 脚本文件的修改时间戳。如果您不想更改 bash 脚本文件的修改时间戳，则必须创建一个单独的文件来存储上次脚本运行时间。
CURRENT_TIME=$(date "+%s")
LAST_SCRIPT_RUN_TIME=$(date -r "$0" "+%s")
TIME_INTERVAL='3600'
START_TIME=$(date -d '07:00:00' "+%s")
END_TIME=$(date -d '16:59:59' "+%s")
TIME_DIFFERENCE=$((${CURRENT_TIME} - ${LAST_SCRIPT_RUN_TIME}))
TIME_CONDITION=$((${START_TIME} <= ${CURRENT_TIME} && ${CURRENT_TIME} <= $END_TIME}))
if [[ "$TIME_DIFFERENCE" -le "$TIME_INTERVAL" ]];
then
>&2 echo "[ERROR] FAILED - script failed to run because of time conditions"
elif [[ "$TIME_CONDITION" = '0' ]];
then
>&2 echo "[ERROR] FAILED - script failed to run because of time conditions"
elif [[ "$TIME_CONDITION" = '1' ]];
then
>&2 touch -m "$0"
>&2 echo "[INFO] RESULT - script ran successfully"
fi
【讨论】：