Shell / command interpreter ● interactive user interface with an operating system ● command line interface (CLI) ● understands and executes the commands a user enters ● outer layer of an operating system (in contrast to the kernel) ● invokes another program, shows the system settings, allows file system modification etc. ● many shells available on a typical Linux/Unix/MacOs systems: sh, bash, zsh, ksh

BASH ● Bourne Again SHell - enhanced version of the original Bourne shell program, sh (written by Steve Bourne) ● on local system: -started after a successful login (if specified in/etc/passwd) -terminal emulators (xterm, gnome-terminal, konsole,... - depends on window manager) ● on remote system : -ssh (Unix, Linux, MacOS,...) -ssh client program e.g. PuTTY

BASH ● interactive shell vanilla:etc root$ ls -al vanilla:etc root$ mkdir backup vanilla:etc root$ mv *.ini backup ● non-interactive shell vanilla:etc root$. script.sh script.s h if [ -d backup ]; then mv *.ini backup else if [ -e backup ]; then echo “Sorry, I can't create \ directory \"backup\" in directory `pwd`” else mkdir backup mv *.ini backup fi

Some linux commands ● grep - search the file or standard input for lines containing a match to the given pattern ● find – find files ● cat - read files sequentially, writing them to the standard output ● wc - print the number of newlines, words, and bytes in files ● ls - list directory contents ● mkdir - create the directories ● rm - remove files and directories (-r) ● cp - copy the contents of the source file to the target file ● mv - rename/move the file ● man - show command manual (man bash, man ls,...) ● whoami - display effective user id (also: id -un or echo "$USER" ) ● who - display a list of all users currently logged on

Redirection ● there are always three default files open: stdin - file descriptor 0 (generally keyboard) stdout - file descriptor 1 (generally screen) stderr - file descriptor 2 (generally screen) ● redirect the standard output to a file ls -alR / > diretorytree.txt ( recursively list all directories in long format starting from /) ● redirect stderr to file cat * 2>errors.txt (writes all errors to the specified file) ● redirect and append stdout to file cat file2.txt>>all.txt ● redirect and append stderr to file cat privatestuff/* 2>>errors.txt

Redirection ● redirect both stdout and stderr to file cp -vrn privatestuff backup &>copy.txt ● redirects stderr to stdout cp -vrn privatestuff backup > copy.txt 2>&1 ● redirect stdin from file wc -l <file.txt writes number of lines in file.txt, the same as: $ wc -l twinkle, twinkle little star ● ^D 2 ● redirect stdin and stdout wc lines.txt

Pipeline ● a set of chained processes, so that the output of each process (stdout) feeds directly as input (stdin) to the next one command1 > file command2 file2 command1|command2|command3 command3 < file2 cat *.txt >file1.tmp sort file2.tmp cat *.txt|sort|uniq uniq <file2.tmp

Variables ● no data types ● can contain a number, a character, a string of characters ● no need to declare a variable, assigning a value to its reference will create it ● value of the variable is retrieved by putting the '$' before name ● dir=”/usr/local/bin” file=”php” echo running $dir/$file... $dir/$file ● capturing a commands output to a variable var=`command` or var=$(command) ● name=`whoami` ● dir=`pwd` ● echo $name is in $dir directory

Environment vs local variables ● global variables or environment variables are available in all shells – use command: $ env SHELL=/bin/bash USER=ania ORACLE_HOME=/Users/oracle/oracle/product/10.2.0/db_1 PATH=/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin:/usr/X11/bin: /Users/oracle/oracle/product/10.2.0/db_1/bin:/Users/oracle/ oracle/product/10.2.0/db_1/bin PWD=/Users/ania LANG=pl_PL.UTF-8 HOME=/Users/ania … ● local variables are only available in the current shell - use the set command to display a list of all variables (including environment ones)

Variables ● making variable a global one $ export VAR=”value” $ ORACLE_HOME=/home/oracle/db_10; export ORACLE_HOME ● removing variable $ unset VAR ● reading variable from stdin $ read VAR ● reserved BASH variables HOME - current user's home directory IFS - list of characters that separate fields PATH - colon-separated list of directories in which the shell looks for commands PS1the primary prompt string UID- numeric real user ID of the current user RANDOMgenerates random integer between 0 and PWDthe current working directory OSTYPE- string describing the operating system HOSTNAME- name of the current host BASH - full pathname used to execute the current instance of Bash and many more...

Pipe examples ● ls -al|grep ^-|tr -s " " " "|cut -f5,9 -d" "|sort -n (show only regular files in the current directory with their size, sorted by size) ● ls -alt|tr -s " " " "|cut -d" " -f9|head -n2|tail -n1 (write name of the last modified file ) ● echo $USER `finger 2>/dev/null|grep $USER|wc -l` (write number of user sessions) ● cat /etc/passwd|sort -t":" -k3 -n|cut -d":" -f1,3 (show users logins with their uid, sorted by uid) ● cat *.java|sort|uniq|wc -l (write number of different lines in all *.java files)

If … then... else... fi ● if condition; then ● command1 command2 … else command3 command4 … ● fi ● conditions test -f file.txt [ -f file.txt ] ((5==5&&6==6)) true ((5<9)) … … …

test ● man test ● [ -f file.txt ] t rue if file exists and is a regular file ● [ -d file.txt ] t rue if file exists and is a directory ● [ -e file.txt ] t rue if file exists (regardless of type) ● [ -z string ] t rue if the length of string is zero ● [ s1 = s2 ] true if the strings s1 and s2 are identical ● [ s1 != s2 ] true if the strings s1 and s2 are not identical. ● [ s1 < s2 ] true if string s1 comes before s2 based on the ASCII value of their characters ●

test ● [ n1 -eq n2 ] true if the integers n1 and n2 are algebraically equal ● [ n1 -ne n2 ] true if the integers n1 and n2 are not algebraically equal ● [ n1 -ge n2 ] true if the integer n1 is algebraically greater than or equal to the integer n2 ● [ n1 -lt n2 ] true if the integer n1 is algebraically less than the integer n2 ● [ ! expression ] true if expression is false ● [ expression1 -a expression2 ] true if both expression1 and expression2 are true. ● [ expression1 -o expression2 ] true if either expression1 or expression2 are true.

no_backup=0; if test -e backup then echo removing directory backup rm -r backup 2>/dev/null no_backup=$? fi if test $no_backup -eq 0 ; then echo creating directory backup mkdir backup echo copying files cp -v *.ini *.conf backup >summary.txt cat summary.txt echo Files copied: cat summary.txt| wc -l else echo Directory \"backup\" can\'t be removed fi

Special parameters $? expands to the exit status of the most recently executed foreground command expands to the positional parameters. when the expansion occurs within double quotes, each parameter expands to a separate word (similar to $*, but $* is no longer recommended) $#expands to the number of positional parameters in decimal. $$Expands to the process ID of the shell. $0Expands to the name of the shell or shell script. ● Parameters $1, $2, $3, …$# $script.sh Script name : script.sh ● command shift script.sh echo Script name: $0 if [ $# -eq 3 ]; then echo $1 echo $2 echo $3 else echo To few parameters fi

While loop ● while condition; do command1 command2 … done ● show script agruments while [ $# -gt 0 ]; do echo $1 shift done

Arithmetic evaluation ● expression evaluation ((expression)) ((i=i+3)) or i=$((i+3)) ● i=$[i + 3] ● i=`expr $i + 3` ● zm=0 while [ $1 ]; do zm=$[zm+$1] shift done echo Sum: $zm

sum=0 first=true while read line; do if ($first); then first=false max=$line min=$line fi if [ $line -gt $max ]; then max=$line fi if [ $line -lt $min ]; then min=$line fi ((sum=sum+line)) done echo Min: $min Max: $max Sum: $sum Script, which finds sum,minimum and maximum from the numbers on the standard input

For loop (1) ● for variable_name [in list] ; do command1 command2 … done ● for (( expr1 ; expr2 ; expr3 )) ; do command1 command2 … done i=1; for param ; do echo Parameter $i: $param i=$((i+1)) done for user in Mike Ann Max do logged=`who|grep $user` if [ "$logged" ];then echo $user logged in else echo $user is not logged in fi done

For loop (2) ● for filedir in * ; do if [ -d "$filedir" ]; then echo Directory: $filedir elif [ -f "$filedir" ];then echo File $filedir fi done ● for ((a=1;a<=$#;a++)); do echo $a : ${!a} done a: … $# ${!a}: $1 $2 $3 ….${$#}

For loop (3) ● for filedir in `ls` ; do if [ -d "$filedir" ]; then echo Directory: $filedir elif [ -f "$filedir" ];then echo File: $filedir else echo Problem: $filedir fi done ● IFS=$'\n' for filedir in `ls -1` ; do if [ -d "$filedir" ]; then echo Directory: $filedir elif [ -f "$filedir" ];then echo File: $filedir else echo Problem: $filedir fi done Wrong solution for a filenames with spaces: File file1.txt File file2.txt Problem: file Problem: with Problem: spaces.txt Good solution for a filenames with spaces: File file1.txt File file2.txt File: file with spaces.txt

Quotes, double quotes ● used where arguments contains spaces ● rm “big file” = rm 'big file' ● mkdir "max ' has ' a dog" creates max ' has ' a dog mkdir 'max “ has “ a dog' creates max “ has “ a dog ● var=1000 echo $var 1000 echo '$var' $var echo “$var” 1000 ● echo * file1.txt file2.txt file3.txt ….. echo '*' * echo “*” * ● escaping echo “\$var” $ var

Functions ● syntax: function_name () { command1 command2... } ● the exit status of a function is the exit status of the last command executed in the body ● executed in the context of the current shell - no new process is created to interpret them ● the arguments to the function become the positional parameters during its execution ● variables are shared between the function and its caller - variables local to the function may be declared with the local builtin command ● if the return command is executed in a function, the function completes and execution resumes with the next command after the function call function function_name { command1 command2... }

max_in () { ( max=0; maxline=""; while read line; do newmax=`echo $line|wc -m ` if [ $newmax -gt $max ] ; then max=$newmax maxline=$line fi done echo $max ":" $maxline )<$1 } for file do if [ -f $file ] then max_in $file fi done Functions Script finds the longest line in every file provided as a parameter

Factorial ● factorial() { if [ $1 -eq 0 ]; then echo 1 else #or: echo $[$1*$(factorial $[$1-1])] #echo $[$1*`factorial $[$1-1]`]; fi } ● factorial2(){ if [ $1 -eq 0 ]; then result=1 else factorial2 $[$1-1] result=$[result*$1] fi } factorial 6 factorial2 6 echo $result