A UNIX/Linux in a nutshell

Transcription

1 bergman p.1/23 A UNIX/Linux in a nutshell Introduction Linux/UNIX Tommi Bergman tommi.bergman[at]csc.fi Computational Environment & Application CSC IT center for science Ltd. Espoo, Finland

2 bergman p.2/23 Contents Introduction Linux/UNIX Small utilities Shell Command line interface Linux/UNIX redirecting Directories and files Linux/UNIX pipes Directory structure Reading text files Contents of a directory More on text files Moving around in the directory tree Environment variables Creating directories Adding and Removing Moving and copying files Shell Scripting Directory and file permissions Config files.emacsrc.bashrc etc. Permissions: adding or removing Command Reference Online help on commands

3 bergman p.3/23 Introduction to UNIX/Linux UNIX/Linux are multitasking operating systems So systems running multiple programs and hosting multiple users at a time usually textual command line shell for command input you can also use GUI(graphical user interface) Same basic system utilities are typically found on both systems These system utilities include small programs for e.g. showing contents for a directory: ls, for copying files: cp, finding text in files: grep

4 bergman p.4/23 The Shell or command line interface Program that enables the user to interact with the computer Most common shells are called bash and tcsh, main differences between shells being syntax and builtin commands Usually commands follow a basic command structure command -options targets Command is sort of a verb and handles the target according to options Linux/UNIX command prompt is case sensitive, so cp command names are usually acronyms of actual words as cp for copy Cp

5 bergman p.5/23 Directory structure The filesystem is organized in a tree-like hierarchial directory structure The uppermost directory in a filesystem is called the root directory Files have a place in one of the directories (tree branches) Command pwd will show you current working directory bergman@c551 bergman> pwd /wrk/bergman/

6 bergman p.6/23 Contents of a directory Command ls(list directory) will show the contents of current directory with different switches you can change the output format yourid@c553 linuxkurssi> ls -la drwxr-xr-x 2 bergman csc 1024 Jan 30 15:47. drwxr-xr-x 4 bergman csc 512 Jan 28 15:02.. -rwx bergman csc Feb 1 13:24 a.out type, permissions,links, owner, group, size, date, name of the file

7 bergman p.7/23 Moving in directory tree Whereas in Graphical user interface you use mouse to navigate through the directories, the cd command is used traverse the directory tree in a command line interface To enter subdirectory inside the current directory cd subdir, for entering parent directory cd.. also explicit path is possible e.g. cd /wrk/userid/new model/

8 bergman p.8/23 Directory and file handling commands To add a directory mkdir and to remove directory rmdir rmdir will only remove directories without content To remove a file command rm is used can also be used to remove directories with option -r which will erase the directory and all its subrirectories When creating files or directories the special characters are tricky, best to avoid using them e.g.?, -, one should especially avoid functions on most shells,/,? and # since they have special

9 bergman p.9/23 Moving and copying files For moving files around the filesystem there are few small commands For copying cp -options oldname new(name/dir) to copy entire folder one must use -r option to recurse the folder Also wildcards: all or part of the filename can be substituted with so called wildcards,?,[a-l] For moving or renaming mv -options oldname new(name/folder) Command history up/down arrows to flick through the previous commands If you have started an unwanted program which takes long to complete one can stop a program execution by pressing Ctrl-C

10 bergman p.10/23 Directory and file permissions All files and directories have a given set of permission attributes The permissions are read, write and/or execute: -rw-r--r-- 1 bergman csc 0 Jan 29 11:04 stuff.txt There are three groups of users The owner, user that has created the file The group, user belongs to at least one group. At CSC, usually group is named after the project leader And the others, that is all other users One can see the users own groups with command groups

11 bergman p.11/23 Permission adding or removing To change the permission there is command chmod ugo(+/-)rwx to add reading rights to user and group: chmod ug+r chmod +r User can also give permissions to users of these groups to use the files that he/she owns and to change the group of the file chgrp Be careful what permissions you give to other users: If you give write permissions to group others, anyone can destroy your important data Usually there is no need to give write permissions to the group other users

12 bergman p.12/23 Online help on commands There are many small commands there is also help features in the shell For shell basic utilities you can find help with info command which will give menu of basic utilities which can be browsed with cursor keys info coreutils The man command works for most programs It prints out manual pages for command in question (e.g. man ls)

13 bergman p.13/23 Linux/UNIX small utilities There are a small utilities that make life a little easier If you have misplaced important file for which you only know the name or part of it. This will find you all files named result yourid@c553:/wrk/yourid> find -name "result" -print For finding text in files yourid@c553:/wrk/yourid> grep pattern file usually you don t want to copy the same file to many different directories. For this purpose it is possible to create symbolic links: ln -s actualfile linkname

14 bergman p.14/23 Linux/UNIX small utilities continued for selecting columns from a file yourid@c553:/wrk/yourid> cut -f 2-3 file You have a list of names you want sort in alphabethical order? This will sort the lines in a file starting in column m and ending in column n sort -k m-n file For substituting parts of the text in (a) file(s) sed e.g. to change all the words dry to word wet yourid@c553:/wrk/yourid> sed s/dry/wet/g blah.txt One can also create aliases for often used commands alias lo logout

15 bergman p.15/23 Linux/UNIX redirecting Shells have a possibility to redirect files or output to commands for giving a file instead of reading from keyboard yourid@c553:/wrk/yourid> cat < names.txt for directing output to a file To print all lines that have string House from file names.txt to file house.txt: yourid@c553:/wrk/yourid> grep House names.txt > house.txt to append output to end of a file To add all lines that have string Road to file house.txt yourid@c553:/wrk/yourid> grep Road names.txt >> house.txt

16 bergman p.16/23 Linux/UNIX pipes It is also possible to redirect output of one program as input to another Almost all commands print result of their actions to standard output which can be redirected to file or as input to other programs using the pipe operator To print out first 10 lines with a string black of the file output.txt: yourid@c553: /testdir> grep black output.txt head [-10]

17 bergman p.17/23 Reading text files Several programs to printout textfiles: less (and more) printout text a screenful at a time, cat will put all on the screen in one go More and less quite similar programs, only More is a lot more primitive and moving about the document is more complex Less can be controlled with arrow and page up/down keys There is also search option with / -key To print a file to terminal screen use cat [option] file cat can also be used to join text files into one cat file1 file2 file3 > bigfile for splitting up a file there is split split -l 10 file.txt

18 bergman p.18/23 More on textfiles For printing only a part from the start or end of the file one can use tail/head [option ] file most common option is -n, where n is the number of lines to print by combining these two one can print some intermidiate part of the file head -100 output tail -5 will print lines To evaluate the size of textfiles we have wc (wordcount) it will tell you how the number of lines, words and bytes the file or files have: Nutshell.tex For editing there is vi and emacs more on these later

19 bergman p.19/23 Environment variables The shell stores information about the current system in environment variables similar to variables in programming languages: environment variable is some data that has a name assigned to it They can be essential to the system opreation or for users own needs purposes e.g. $PATH command search path, $HOME home directory, $LPDEST current printer or $IMPORTANT FILES

20 bergman p.20/23 Environment variables continued To see all current environment variables env They are userdefinable, but to add you must include the current variable to the list of values tcsh:setenv PATH ($PATH /some/new/directory/) bash:export PATH=$PATH:/some/new/directory/ NB! environment variables are used with a $-sign, but are set without

21 bergman p.21/23 Shell scripting Commands can be written to a text file to create scripts, so it is possible to automate even complex tasks They can be executed using shell-interpreter(sh scriptfile) or by changing file permission to execute Most of the normal programming language constructs are available as e.g If-then-else for conditional branches and for-loops Small example: for f in do.txt echo sorting file $f cat $f sort $f.sorted echo sorted file has been output to $f.sorted done

22 bergman p.22/23 Config files.emacsrc.bashrc etc. Config files are often called the dot-files for their naming conventions(.config) and stored at the users home directory These can include almost any information from work directory to redefining keyboard commands When logging on the shell will process.login and.bashrc files These are normal script files They include usually environment variables and aliases, advanced users may include many automated tasks to be run when logging on

23 bergman p.23/23 Small command reference card cd folder move to folder export PRINTER=spoolprint (bash) set environment ls show contents of folder set PRINTER spoolprint (tcsh) variable PRINTER rm remove file find -name foot -print find file with foot in the name cp for copying files env show environment variables rmdir remove directory ln -s file linkname create a link to file mkdir make directory sort file sort lines in file cat concatenate scp secure copy grep print lines with certain string head -n file show n first lines of file chmod change permissions tail -n file show n last lines of file less file show file screenful at a time cut -f n-m file cut columns n to m from file