Shell 脚本专家指南学习笔记1

最新推荐文章于 2025-02-27 17:13:06 发布

ysdaniel

最新推荐文章于 2025-02-27 17:13:06 发布

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分类专栏： Shell linux 文章标签： shell 脚本 command variables attributes interface

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Shell脚本的错误检测

set - 打开某个选项，例如set -x；

set + 关闭某个选项，例如set +x；

这样就能精确控制调试某一段的代码，在不需要调试的地方关闭选项。

1、如果脚本文件中加入了命令set -x ，那么在set命令之后执行的每一条命令以及加在命令行中的任何参数（包括变量和变量的值）都会显示出来。每一行之前都会加上加号（+），提示它是跟踪输出的标识。在子Shell中执行的Shell跟踪命令会加两个加号，即“++”。

2、set -v 选项打开冗余模式，能打印出调试语句。

3、根据调试层次控制输出，用于多层次调试：在脚本开始部分设置一个调试变量。脚本运行时测试该变量，然后根据变量的值决定是显示还是禁止调试指令。

例如：

#！/bin/bash

debug=3
test $debug -gt 1 && echo "Debug is bigger than 1."
test $debug -gt 2 && echo "Debug is bigger than 2."
……

/etc/shadow中用户账号信息的第三个字段保存的是该账户的口令最后一次更改的时间，记录形式从1970年1月1日到该时间的天数。UNIX和Linux都是从1970年1月1日开始计算时间的。

[root@localhost ~]# tail -3 /etc/shadow
tomcat:!!:15261::::::
tom:$6$y6Glr2jNfeFeokEP$Fiov9oRVKKOT9tHhL4ZrgS6WMarI4QuFBWyEOlivFbOPxezJN5PltO5xTlhz4Qxa3B0cuUHghDVJey5cXUv590:15261:0:99999:7:::
jack:$6$WngWxvov$EgAcspKEwnllJ1mpCiCjt.O5wgewhdEFP6Prkx2g.Z6z9LusXyZeFUZe5V3kzzWvhvIH9Bg5K6NGZEicQfHiw1:15287:0:99999:7:::

date +%s 直接返回纪元（1970年1月1日）以来的秒数。
[root@localhost ~]# date +%s
1321600930

[root@localhost ~]# help set
set: set [--abefhkmnptuvxBCHP] [-o option-name] [arg ...]
   Set or unset values of shell options and positional parameters.

   Change the value of shell attributes and positional parameters, or
   display the names and values of shell variables.

   Options:
   -a Mark variables which are modified or created for export.
   -b Notify of job termination immediately.
   -e Exit immediately if a command exits with a non-zero status.
   -f Disable file name generation (globbing).
   -h Remember the location of commands as they are looked up.
   -k All assignment arguments are placed in the environment for a
   command, not just those that precede the command name.
   -m Job control is enabled.
   -n Read commands but do not execute them.
   -o option-name
   Set the variable corresponding to option-name:
   allexport same as -a
   braceexpand same as -B
   emacs use an emacs-style line editing interface
   errexit same as -e
   errtrace same as -E
   functrace same as -T
   hashall same as -h
   histexpand same as -H
   history enable command history
   ignoreeof the shell will not exit upon reading EOF
   interactive-comments
   allow comments to appear in interactive commands
   keyword same as -k
   monitor same as -m
   noclobber same as -C
   noexec same as -n
   noglob same as -f
   nolog currently accepted but ignored
   notify same as -b
   nounset same as -u
   onecmd same as -t
   physical same as -P
   pipefail the return value of a pipeline is the status of
   the last command to exit with a non-zero status,
   or zero if no command exited with a non-zero status
   posix change the behavior of bash where the default
   operation differs from the Posix standard to
   match the standard
   privileged same as -p
   verbose same as -v
   vi use a vi-style line editing interface
   xtrace same as -x
   -p Turned on whenever the real and effective user ids do not match.
   Disables processing of the $ENV file and importing of shell
   functions. Turning this option off causes the effective uid and
   gid to be set to the real uid and gid.
   -t Exit after reading and executing one command.
   -u Treat unset variables as an error when substituting.
   -v Print shell input lines as they are read.
   -x Print commands and their arguments as they are executed.
   -B the shell will perform brace expansion
   -C If set, disallow existing regular files to be overwritten
   by redirection of output.
   -E If set, the ERR trap is inherited by shell functions.
   -H Enable ! style history substitution. This flag is on
   by default when the shell is interactive.
   -P If set, do not follow symbolic links when executing commands
   such as cd which change the current directory.
   -T If set, the DEBUG trap is inherited by shell functions.
   - Assign any remaining arguments to the positional parameters.
   The -x and -v options are turned off.

-a &&