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最新推荐文章于 2024-03-04 11:18:01 发布

jevens17

最新推荐文章于 2024-03-04 11:18:01 发布

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文章标签： bash date shell login pthreads 正则表达式

本文链接：https://blog.youkuaiyun.com/jevens17/article/details/6084190

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1. HISTTIMEFORMAT 变量：bash3.0推出的新变量，记录历史命令的执行时间

譬如：HISTTIMEFORMAT="[%F %T]"

执行history，显示：

    490 [2008-07-16 15:12:23]HISTTIMEFORMAT="[%F %T]"
    491 [2008-07-16 15:12:25]history
    492 [2008-07-16 15:12:32]man date

2. date 命令和strftime 函数，扩展clock、hwclock

date命令：print or set the system date and time

strftime函数：awk调用了类型为time_t的c函数库 strftime([format [, timestamp]])

功能：Formats timestamp according to the specification in format.

systime函数：同上，Returns the current time of day as the number of seconds since the Epoch systime()

譬如：设置系统时间：date -s "12/29/2008 18:00:00"

display系统时间：date -d "+3 day" + "%F %T" date -d "-3 years" + "%F %T"

毫秒级时间戳->格式化时间：echo 12879350 | awk '{print strftime("%F %T", $0)}'

格式化时间->毫秒级时间戳：date -s把当前时间设置成special time，然后 awk '{print systime()}'即可如：echo "05/05/2008" |awk '{print systime()}'

3.扩展的正则表达式- extended expression

包括： () | + ? 譬如：(a|b|c)+d?

grep只支持basic regexp，egrep支持extended regexp，所以() | + ?只在egrep中有效，或者grep -E

sed无效，sed -r有效；awk有效。看man手册即可

4. ps命令中的status状态 bash3.0以上支持(kernel 2.6以上)

    D Uninterruptible sleep (usually IO)
    R Running or runnable (on run queue) 运行中
    S Interruptible sleep (waiting for an event to complete) 可打断的后台进程，类似守护进程httpd、ntpd、crond等
    T Stopped, either by a job control signal or because it is being traced.
    W paging (not valid since the 2.6.xx kernel)
    X dead (should never be seen)
    Z Defunct ("zombie") process, terminated but not reaped by its parent.

    For BSD formats and when the stat keyword is used, additional characters may be displayed:
    < high-priority (not nice to other users) 高优先级
    N low-priority (nice to other users) 低优先级
    L has pages locked into memory (for real-time and custom IO)
    s is a session leader 主进程
    l is multi-threaded (using CLONE_THREAD, like NPTL pthreads do) 表示线程
    + is in the foreground process group 前台运行

譬如：ps -axuf后status column中：Ss表示父进程、R+正在前台运行的进程、SN表示低优先级的进程，S+、Sl表示线程、SL等

5. su和login shell

non-login shell则仅执行/etc/bashrc和.bashrc

查看su的man手册，su - 切换用户将会使用login shell；不带-的话，则会使用non-login shell

PS：在RHEL下，辨别login和non-login shell另外一种方法是：exit命令后如果会清屏则是login shell，反之则是non-login shell