Unix/linux System Management Technical Manual study notes--shell

Date Created: 2016/02/29

Update on: 2016/02/29

1. Shell variables cannot be left blank on both sides of the equals sign, otherwise the shell will mistake the variable name for the command name
2. Variables enclosed in double quotes can be replaced with * and? The file name matches the meta-character extension) and the variable extension, and the single quotation marks do not handle the variable.
3. The left quotation mark ', which handles a mechanism similar to a double quote, is able to execute the contents of a string as a shell command, and then replace the string with the output.
4. Cut: Divides the row into fields, the default qualifier is tab, you can change the qualifier with the-D option, and the-F option specifies which fields the output contains.
5. Bash +x: The command will be printed before executing a command.
6. The-n option of the echo command eliminates the usual line breaks.
7. A command-line argument to a script can be a variable: $ $ for the first, $ $ for the second, and $ for the name (script name) used to invoke the script, $ #为命令行参数的个数, $* for all parameters, none of these 2 are counted as $ A.
8. $? succeeded to 0 for the status of the last execution of the command exit. If it is not successful then the other parameter 1-255, called in the script also represents the state in the previous command (will be updated in real time), and when a script exit 100, then the% value becomes 100. The return value of exit can therefore be used to determine the execution state of the script.

Unix/linux System Management Technical Manual study notes--shell