Upades of the scripting chapter, added another script example.

Signed-off-by: V-Z <vojta@trapa.cz>

Author: V-Z

presentation/linux_bash_metacentrum_course.tex

@@ -3116,6 +3116,7 @@ \subsection{Basic skeleton}
 		\item Launch with \texttt{./noninteractive.sh}
 		\item The most simple script:
 	\end{itemize}
+	\vfill
 	\begin{bashcode}
     #!/bin/bash
     # Simple non-interactive script - no communication with user
@@ -3126,26 +3127,11 @@ \subsection{Basic skeleton}
 	\end{bashcode}
 \end{frame}
 
-\subsection{BASH variables}
-
-\begin{frame}{Special variables available in the script (selection)}
-	\begin{itemize}
-		\item \alert{\texttt{\$1}},~\ldots~(number from \texttt{1} up to number of parameters) --- individual positional parameters (see further for example)
-		\item \alert{\texttt{\$0}} --- path of the starting script
-		\item \alert{\texttt{\$\#}} --- number of command-line arguments
-		\item \alert{\texttt{\$*}} --- all of the positional parameters, seen as a~single word, must be quoted (i.e. \texttt{"\$*"})
-		\item \alert{\texttt{\$@}} --- same as \texttt{\$*}, but each parameter is a~quoted string --- the parameters are passed on intact, without interpretation or expansion, each parameter in the argument list is seen as a~separate word, should be quoted (i.e. something like \texttt{"\$@"})
-		\item \alert{\texttt{\$\$}} --- process ID (PID) of the script itself
-		\item \alert{\texttt{\$?}} --- Exit status of previous command, function, or the script itself
-		\item \href{https://www.tldp.org/LDP/abs/html/internalvariables.html}{See more variables\ldots}
-	\end{itemize}
-\end{frame}
-
 \subsection{Functions}
 
 \begin{frame}[fragile]{Functions in BASH}{Pieces of code, which can be used repeatedly}
 	\begin{bashcode}
-    # Declare new function
+    # Declare new function within script
     function MyNewFunction1 {
       echo "Hello, $USER from $(groups) on $HOSTNAME!"
       }
@@ -3165,11 +3151,27 @@ \subsection{Functions}
 	\end{bashcode}
 \end{frame}
 
+\subsection{BASH variables}
+
+\begin{frame}{Special variables available in the script (selection)}
+	\begin{itemize}
+		\item These variables can be used within script e.g. to parse arguments provided by the user
+		\item \alert{\texttt{\$1}},~\ldots~(number from \texttt{1} up to number of parameters) --- individual positional parameters (see further for example)
+		\item \alert{\texttt{\$0}} --- path of the starting script
+		\item \alert{\texttt{\$\#}} --- number of command-line arguments
+		\item \alert{\texttt{\$*}} --- all of the positional parameters, seen as a~single word, must be quoted (i.e. \texttt{"\$*"})
+		\item \alert{\texttt{\$@}} --- same as \texttt{\$*}, but each parameter is a~quoted string --- the parameters are passed on intact, without interpretation or expansion, each parameter in the argument list is seen as a~separate word, should be quoted (i.e. something like \texttt{"\$@"})
+		\item \alert{\texttt{\$\$}} --- process ID (PID) of the script itself
+		\item \alert{\texttt{\$?}} --- Exit status of previous command, function, or the script itself
+		\item \href{https://www.tldp.org/LDP/abs/html/internalvariables.html}{See more variables\ldots}
+	\end{itemize}
+\end{frame}
+
 \subsection{Reading variables}
 
 \begin{frame}{It is important to check user input\ldots}
 	\begin{center}
-		\includegraphics[width=7.5cm]{exploits_of_a_mom.png}
+		\includegraphics[width=8cm]{exploits_of_a_mom.png}
 	\end{center}
 	\begin{flushright}
 		\url{https://xkcd.com/327/}
@@ -3178,7 +3180,7 @@ \subsection{Reading variables}
 		\item By accident or purpose (attack), user can enter unexpected value
 		\begin{itemize}
 			\item In the \enquote{best} case, the script \enquote{just} crashes
-			\item Script can behave unexpectedly, returning very weird results
+			\item Script can behave unexpectedly, returning very weird results, damage data
 			\item Internal functions/commands can return error messages, which are hard to understand
 			\item Attacker can e.g. modify web content (\href{https://en.wikipedia.org/wiki/Cross-site_scripting}{XSS},~\ldots), obtain private data, root privileges,~\ldots
 		\end{itemize}
@@ -3246,6 +3248,7 @@ \subsection{Reading variables}
 	\begin{itemize}
 		\item Detailed explanations of all features used here are in various following slides\ldots{ }See scripts \texttt{interactive2\{whiles,functions\}.sh}
 	\end{itemize}
+	\vfill
 	\begin{bashcode}
     ... # Following code replace lines 3 and 4 from previous script
     NUMBER='^[0-9]+$'
@@ -3379,6 +3382,7 @@ \subsection{Reading variables}
 		\item See \texttt{interactive5.sh} for complete example
 		\item \texttt{getopts} reads short (one-letter) parameters, they can have input value (marked by \texttt{:})
 	\end{itemize}
+	\vfill
 	\begin{bashcode}
     #!/bin/bash
     # All provided values are evaluated in while cycles...
@@ -3471,6 +3475,31 @@ \subsection{Reading variables}
 	\end{bashcode}
 \end{frame}
 
+\begin{frame}[fragile]{Simple providing of input file}
+	\begin{bashcode}
+    #!/bin/bash
+    # We expect exactly one parameter
+    if [ "$#" -ne "1" ]; then
+      echo "Error! Exactly one parameter is required!"
+      exit 1
+      fi
+    # Verify that file exists and is readable
+    if [ ! -r "$1" ]; then
+      echo "Error! The file provided does not exist or is not readable!"
+      exit 1
+      fi
+    # Do the operation with input file..
+    echo "Size of the file is $(du -sh "$1" | cut -f 1)."
+    echo "The file has $(wc -l "$1" | cut -d ' ' -f 1) lines."
+    echo "Making backup of the file $1..."
+    cp "$1" "$1".bak || { echo "Error! Making backup of $1 failed!"; exit 1; }
+    echo "Done!"
+    exit
+    # Use the script with some text file...
+    ./interactive6.sh long_text.txt
+	\end{bashcode}
+\end{frame}
+
 \subsection{Branching the code}
 
 \begin{frame}[fragile]{If branching (examples are elsewhere)}
@@ -3505,14 +3534,14 @@ \subsection{Branching the code}
 			\begin{itemize}
 				\item Escaping variables and values by double quotes (\texttt{"}\ldots\texttt{"}) is recommended (to be sure), but not strictly required all the time
 			\end{itemize}
-			\item \texttt{if [ ! -f regularfile ];} \ldots --- reverted condition (\texttt{!})
+			\item \texttt{if [ !} -\texttt{f regularfile ];} \ldots --- reverted condition (\texttt{!})
 			\item Single-bracket conditions --- file, string, or arithmetic conditions
 			\item Double-bracket syntax --- enhanced
 			\begin{itemize}
 				\item Allow usage of regular expressions and globing patterns
 				\item Word splitting is prevented --- \texttt{\$STRINGVAR} can contain spaces
-				\item Expanding file names --- \texttt{if [[ -a *.sh ]]} (variant with only one bracket doesn't work when there are multiple sh files)
-				\item Allows more detailed test, e.g. \texttt{if [[ \$num -eq 3 \&\& "\$STRINGVAR" == XXX ]] \ldots}
+				\item Expanding file names --- \texttt{if [[} -\texttt{a *.sh ]]} (variant with only one bracket doesn't work when there are multiple sh files)
+				\item Allows more detailed test, e.g. \texttt{if [[ \$num} -\texttt{eq 3 \&\& "\$STRINGVAR" == XXX ]] \ldots}
 			\end{itemize}
 		\end{itemize}
 		\item -\texttt{eq} --- Equal to
@@ -3531,8 +3560,8 @@ \subsection{Branching the code}
 		\item \texttt{\$STR1 == \$STR2} --- True if both strings are equal
 		\item \texttt{\$STR} --- True if string \texttt{\$STR} is assigned a~value and is not null
 		\item \texttt{\$STR1 != \$STR2} --- True if both strings are unequal
-		\item -\texttt{a} --- Performs the \texttt{AND} function (\texttt{[ \ldots -a \ldots~]} or \texttt{[ \ldots~] \&\& [ \ldots~]})
-		\item -\texttt{o} --- Performs the \texttt{OR} function (\texttt{[ \ldots -o \ldots~]} or \texttt{[ \ldots~] || [ \ldots~]})
+		\item -\texttt{a} --- Performs the \texttt{AND} function (\texttt{[ \ldots} -\texttt{a \ldots~]} or \texttt{[ \ldots~] \&\& [ \ldots~]})
+		\item -\texttt{o} --- Performs the \texttt{OR} function (\texttt{[ \ldots} -\texttt{o \ldots~]} or \texttt{[ \ldots~] || [ \ldots~]})
 		\item Do not confuse globing patterns and regular expressions when using \texttt{[[ \ldots~]]}
 		\begin{itemize}
 			\item Shell globing: \texttt{if [[ "\$STRINGVAR" \textbf{==} ?[sS]tring* ]]; then} --- \texttt{?} represents single character \texttt{[]} any character inside and \texttt{*} zero or more characters
@@ -3548,6 +3577,7 @@ \subsection{Branching the code}
 		\item RAxML binaries must be in \texttt{\$PATH}
 		\item See \texttt{raxml\_if.sh} for whole script
 	\end{itemize}
+	\vfill
 	\begin{bashcode}
     if grep -iq avx2 /proc/cpuinfo; then # Does the CPU support AVX2?
       RAXML='raxmlHPC-AVX2' # Select appropriate binary
@@ -3567,6 +3597,7 @@ \subsection{Branching the code}
 		\item Same task as on previous slide, but instead of if-then branching it is using \texttt{case}
 		\item See \texttt{raxml\_case.sh} for whole script
 	\end{itemize}
+	\vfill
 	\begin{bashcode}
     # Determine which CPU is available and which binary use then
     CPUFLAGS=$(grep -i flags /proc/cpuinfo | uniq)
@@ -3597,7 +3628,7 @@ \subsection{Loops}
     for JPGF in *.jpg; do convert $JPGF -resize 100x100 thumbs-$JPGF; done
     # More commands in a block
     for JPGF in $(ls -1 *.jpg); do
-      echo "Processing JPGF $JPGF"
+      echo "Processing JPG $JPGF"
       convert $JPGF -resize 100x100 thumbs-$JPGF
       echo "File thumbs-$file created"
       done
@@ -3614,8 +3645,7 @@ \subsection{Loops}
 	\begin{bashcode}
     # while cycle is evaluating condition and if it is equal to 0 (TRUE)
     # the cycle body is launched, repeatedly while the condition is met
-    while condition
-      do
+    while condition; do
         commands
       done
     # Like while cycle, but until condition is not equal to zero
@@ -3627,7 +3657,7 @@ \subsection{Loops}
       if [condition]; then # If something happens
         break; fi # End up the cycles and continue by following commands
     while read TEXTLINE; do # Run cycles on text file
-      commands...
+      commands... # TEXTLINE contains in each cycle one line of the file
       done < text_file_to_process.txt
     while :; do echo "Press CTRL+C to exit..."; done # Infinite loop
     for (( ; ; )) ; do echo "Press CTRL+C to exit..."; done # Infinite loop

scripts_data/interactive6.sh

@@ -0,0 +1,24 @@
+#!/bin/bash
+
+# We expect exactly one parameter
+if [ "$#" -ne "1" ]; then
+	echo "Error! Exactly one parameter is required!"
+	exit 1
+	fi
+
+# Verify that file exists and is readable
+if [ ! -r "$1" ]; then
+	echo "Error! The file provided does not exist or is not readable!"
+	exit 1
+	fi
+
+# Do the operation with input file..
+echo "Size of the file is $(du -sh "$1" | cut -f 1)."
+echo "The file has $(wc -l "$1" | cut -d ' ' -f 1) lines."
+
+echo "Making backup of the file $1..."
+cp "$1" "$1".bak || { echo "Error! Making backup of $1 failed!"; exit 1; }
+
+echo "Done!"
+
+exit