Operating systems 1 -- 2008-2009 -- info.uvt.ro/Laboratory 2

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Võro system paths

• examples:
  • absolute paths:

/home/ciprian/test.sh
/tmp

• • relative paths:

./test.sh
a/b/c
../a/b/c
test.sh

• • ~ expansion:

~/abc

Zulu bash commands

POP PLAYER commands

• syntax:
  • a list of blank separated words (strings);
  • the first word specifies the command to be invoked;
  • the remaining words are passed as arguments;
  • the end is marked by a control character:
    • end of line;
    • &, &&, ||, ;;

<command> [<argument>] ...

• examples:
  • prints Hello world:

echo Hello world!
echo 'Hello world!'

• • displays the manual page for bash:
    • use q to exit;

man bash

• • displays the current user:

whoami

List of commands

• syntax:
  • a list of simple commands;
  • separated by: ;, &&, ||;
  • optionally terminated by ; or &;
  • attention to the spacing;

<command> [argument] ... { <; | && | ||> <command> [argument] ... } ...

• example:
  • displays hello world on two distinct lines:

echo hello ; echo world

• • displays the date at two seconds apart:

date ; sleep 2 ; date

Comments

• in almost all situations characters following a # and up to the end of the line are treated as a comment:

echo a # b c

Basic bash script

• editing:

nano ./test.sh

• example script:

#!/bin/bash
echo hello world
exit 0

• making it executable:

chmod +x ./test.sh

• executing it:

./test.sh

• references:
  • Advanced Bash-Scripting Guide -- Starting Off With a Sha-Bang;

Generic commands

• references:
  • echo.1;
  • date.1;
  • sleep.1;
  • whoami.1;
  • Advanced Bash-Scripting Guide -- Internal Commands and Builtins;

File system commands

• references:
  • Advanced Bash-Scripting Guide -- Basic Commands;

Current directory

• syntax:

pwd
cd
cd <directory>

• examples:

pwd
cd /tmp
pwd
cd
pwd

• references:
  • cd.1;
  • pwd.1;

Viewing

cat

• syntax:

cat [flag] ... [files] ...

• example:

cat ./test.sh
cat -n ./test.sh

• important flags:
  • -b or --number-nonblank;
  • -n or --number;
  • -s or --squeeze-nonblank;
• references:
  • cat.1;

stat and file

• syntax:

stat <file> ...
file <file> ...

• examples:
  • detailed information about a file or directory:

stat /etc
stat /etc/group

• • type information about a file or directory:

file /etc/group
file /bin/bash

• references:
  • stat.1;
  • file.1;

less and more

• syntax:

less [file]
more [file]

• examples:
  • displays the content of the /etc/services file:
    • use q to exit;

less /etc/services
more /etc/services
cat /etc/services | less

• references:
  • less.1;
  • more.1;

Directory creation

• syntax:

mkdir [flag] ... <directory>

• example:
  • shows that the directory dir1 does not exist (in the current working directory);
  • creates the directory dir1;

stat ./dir1
mkdir ./dir1
stat ./dir1

• • creates a directory and its parents:

mkdir ./dir2/dir3
mkdir -p ./dir2/dir3

• important flags:
  • -p or --parrents;
• references:
  • mkdir.1;

Directory deletion

• syntax:

rmdir [flag] ... <directory>

• example:
  • deletes the empty folder dir1:

stat ./dir1
rmdir ./dir1
stat ./dir1

• • deletes the empty folder and its (empty parents):

rmdir ./dir2/dir3
rmdir -p ./dir2/dir3

• important flags:
  • -p or --parrents;
• references:
  • rmdir.1;

File creation

• syntax:

touch <file>

• example:
  • shows that the file file1 does not exist and creates it:

stat ./file1
touch ./file1

• • shows that if the file already exists it's left as it is (only the timestamp is modified):

stat ./file1
touch ./file1
stat ./file1

• references:
  • nano.1;
  • touch.1;

File deletion

• syntax:

rm [flag] ... <file> ...

• example:
  • deletes the file file1

stat ./file1
rm ./file1
stat ./file1

• • it demonstrates that we can not delete a directory that contains files or other folders:

mkdir dir4
touch dir4/file4
rm dir4

• • we have to delete its children first:

rm dir4/file4 dir4

• • or we can use the -R (recursive) flag to delete the directory and its children in one step:

mkdir dir5
touch dir5/file5
rm -R dir5

• important flags:
  • -i or --interactive;
  • -R or --recursive;
• references:
  • rm.1;
  • for safer deletion use: shred.1;

Copying

• syntax:

cp [flag] ... <sourc> <target>

• example:
  • copying only one file:

cp /etc/group .
stat ./group

• • copying one file under a new name:

cp /etc/passwd ./passwd-copyied
stat ./passwd-copyied

• • creating a directory hierarchy:

mkdir ./dir6
cp ./group ./dir6
stat ./dir6/group

• • trying to copy a directory (does not work unless we give it the -R flag):

cp ./dir6 ./dir7

• • using the -R flag:

cp -R ./dir6 ./dir7
stat ./dir7/group

• • showing that cp overwrites the destination file (if it exists):

cat ./group
cp /etc/passwd ./group
cat ./group

• important flags:
  • -i or --interactive;
  • -R or --recursive;
• references:
  • cp.1;

Moving

• syntax:

mv [flag] ... <sourc> <target>

• examples:
  • renaming a directory under one that already exists should not work:

stat ./dir6
stat ./dir7
mv ./dir6 ./dir7

• • but we can rename it under a name that does not exist:
    • we demonstrate that mv moves the entire hierarchy (without -R);

mv ./dir6 ./dir8
stat ./dir8/group

• • mv overwrites the destination file (just like cp):

cat ./passwd-copyied
cp /etc/group ./group
cat ./group
mv ./passwd-copyed ./group
cat ./group

• important flags:
  • -i or --interactive;
  • -R or --recursive;
• references:
  • mv.1;

Querying

ls

• syntax

ls [flag] ... <directory>

• examples:

ls /tmp
ls ~
ls -a ~
ls -l ~
ls -a -l ~
ls -al ~
ls /etc
ls -1 /etc

• important flags:
  • -a or -A;
  • -l (with -h and / or -n);
  • -1;
• references:
  • ls.1;

find

• syntax:

find <directory> [test] ... [action] ...

• examples:

find /etc
find /etc -type d
find /etc -type f
find /etc -name 'g*'

• important (flags) tests:
  • -type;
  • -name and -iname;
• important actions:
  • -print;
  • -ls;
  • -exec;
• references:
  • find.1;

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• Ciprian Dorin Crăciun, ccraciun@info.uvt.ro