Linux 学习记录

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背景

这是一个很好的学习Linux的资源。

记录一些看教程时发现的自己还不了解的点。

注：

  1. 【申时】哺时，又名日铺、夕食等（15时至17时）。

  2. 【拾遗】采补缺漏遗佚。《南齐书．卷九．礼志上》：吴则太史令丁孚拾遗汉事，蜀则孟光、许慈草建众典。

重定向 Redirection

1. Redirecting input/output

1
command > file

redirect standard output to a file.

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command >> file

append standard output to a file.

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command < file

redirect standard input from a file.

2. Pipes

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command1 | command2

pipe the output of command1 to the input of command2.

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cat file1 file2 > file0

concatenate file1 and file2 to file0.

Wildcards

1. The * (asterisk) wildcard

  • * match any number of characters.

2. The ? (question mark) wildcard

  • ? match one character.

Some Uesful Commands

commands Funcition
df reports on the space left on the file system
quota check amount of disk space quota you have
du outputs the number of kilobyes used by each subdirectory
apropos not sure of the exact name of a command
gzip compress the file to *.gz
gunzip expand the *.gz file
tar -cvf file compress the file tot *.tar
tar -xvf file expand the *.tar file
file classifies the named files according to the type of data they contain
diff file1 file2 compares the contents of two files and displays the differences
find; find . -name “*.txt” -print; find . -size +1M -ls searches through the directories for files and directories with a given name, date, size, or any other attribute you care to specify

UNIX Variables

1. Intro

  • Variables are a way of passing information from the shell to programs when you run them.

  • Standard UNIX variables are split into two categories, environment variables and shell variables.

    1. Shell variables apply only to the current instance of the shell and are used to set short-term working conditions; Shell variables have lower case names.
  1. Environment variables have a farther reaching significance, and those set at login are valid for the duration of the session. Environment variables have UPPER CASE.
  2. Variables all start with a “$” mark.

2. Environment Variables

Show environment variables

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% echo $OSTYPE

More e.g.:

  • USER (your login name)
  • HOME (the path name of your home directory)
  • HOST (the name of the computer you are using)
  • ARCH (the architecture of the computers processor)
  • DISPLAY (the name of the computer screen to display X windows)
  • PRINTER (the default printer to send print jobs)
  • PATH (the directories the shell should search to find a command)

Check values of the variables

  • setenv set environment variables.

  • unsetenv unset environment variables.

  • printenv & env display:

    1
    % printenv | less

3. Shell Variables

Show

1
% echo $history

More e.g.:

  • cwd (your current working directory)
  • home (the path name of your home directory)
  • prompt (the text string used to prompt for interactive commands shell your login shell)
  • path (the directories the shell should search to find a command)

Check values of the variables

  • set

  • unset

  • 1
    % set | less

4. Setting shell variables in .cshrc

  • set history=200 only works in current shell, so it works for only once.

  • gedit ~/.cshrc add the lines after all other lines:

set history = 200

Save the file and reload it:

source ~/.cshrc

Check whether it works or not:

echo $history

5. Setting the path

  • path/PATH variable defines in which directories the shell will look to find the cmommand you typed.

  • set path = ($path ~/units174/bin) only works for once

  • add the following line to .cshrc to add path permanently

    set path = ($path ~/units174/bin)