BreadCrumbs: Bash

Bash

From Luke Jackson

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Shells

What is a shell? The short answer is that it is a command interpreter. It is what allows you to interact with the system from the console. That is, it is what locates and starts programs for you. It also has builtin commands and is, infact, a complete programming language. Most of the init scripts on a Linux system are written in bash, peruse the files in /etc/rc.d/init.d in order to see examples of bash scripts.

Bash is not the only shell available, there are many others: sh, ash, tcsh, csh, pdksh, ksh, sash, zsh, etc... Bash happens to be the default shell in most Linux distributions. BTW, the name, 'Bash', stands for 'Bourne Again SHell' -- a pun on the original UNIX shell, sh, written by Steve Bourne. Bash is an improved reimplementation of sh, largely POSIX compliant.

 Upon exit, ~/.bash_logout is executed in order to clean up after the shell.
+=== Profile ===
+ export HISTFILESIZE=50000
+ export HISTSIZE=50000
+ export HISTCONTROL=ignoredups
 == Bash Scripting ==
 * How to find out more about bash:
 there is a lot of information in the info page about bash. Type: info bash, in order to read the info page. The trouble about the info page, though, is that it was written by programmers for programmers... One book that I have is called 'Learning the Bash Shell', by Newham and Rosenblatt, published by O'Reilly ( http://www.oreilly.com ). This book is good for beginners, building up from a presumed minimal knowledge set to some fairly advanced programming.
+== Execution ==
+The shell locates and executes programs whose names you enter on the command line. It finds the programs by searching through a subset of the filesystem specified by the PATH environment variable. In order to see the contents of you PATH, type echo $PATH. Note that as root, you should never have a PATH that includes '.' -- there is the story of a bofh who was duped by some junior admins who needed access to some part of the machine (which he wouldn't grant them; they put a rootkit of some sort in a directory, named it 'ls' and then complained to the bofh that they were having problems with the directory; he changed to the directory, typed 'ls' in order to see what was there, and was promptly rooted...
+== Aliases ==
+Aliases are short text strings that the shell substitutes for patterns that it sees on the command line. There are a number of system aliases on most versions of Linux such as aliasing cp against cp -i ( the -i switch means 'interactive', i.e., ask before overwriting ( or removing, in the case of rm -i )). The builtin alias will list all aliases that apply to your current shell. In order to specify an new alias, type alias ll="ls -l" ( this is a common alias already on your machine ). ll is the alias, "ls -l" is the command it's aliased against. Note that it is double quote enclosed -- that is due to there being a space in the text string -- if there are no spaces, then the quotes are not needed. In order to make the alias permanent, place it in your ~/.bashrc script.
+== History ==
+Bash provides an execllent history mechanism to allow you to re-execute previous commands with minimal typing. Each command that you type is kept in ~/.bash_history in order ( take a look at it with less ). You can also view your history by typing history -- the history builtin numbers the commands for you. Typing history 10 will list the last ten entries in your history file. You can select a command and rerun it by typing !999, where '999' is the number of the command. That is called 'bang execution'. You can also type the bang and the first few letters of the command -- bash will search backward through your history file to find the firs match and will run that. The simplest thing is to just use the up/down arrow keys in order to scroll through your previous commands -- when you get to one that you like, hit either TAB in order to edit it or RETURN in order to rerun it. You can also use the builtin fc, 'fix command', in order to select a range ( or single ) command for re-execution. fc puts the commands into a text editor session ( vi by default ) so that you can edit ( fix ) them before running them. The commands are run when you exit the editor -- in order to not run them, delete them... The format for fc is fc 900 950 where '900' is the first command to run and '950' is the last.
+== IO Streams & Redirection ==
+The power of UNIX comes from its root philosophy, that of the toolbox approach. Software bloat comes from trying to write monolithic applications that aspire to be and do everything, emacs, for instance ;) The defining ideas of unix are that everything is a text stream and that programs should be small and do one thing well. Such small programs are called filters. Where the power comes in is in the ability to redirect the output of one filter to the input of another.
+In order to do this, you should understand unix I/O. Input and Output are divided into three streams. A stream is a long series of characters, 8 bits per character on x86/Linux. Realize that the files on your computer are simply long, ordered sequences of characters terminated by NULL bytes ( abbreviated '\0' in C ). The three streams are:
+* fd0 - standard input, abbreviated stdin,
+* fd1 - standard output, stdout, and
+* fd2 - standard error, stderr.
+Standard input is normally attached to ( taken from ) the keyboard. It is designated 'file descriptor 0'. Standard output is normally attached to ( sends to ) the monitor ( terminal ). It is designated 'file descriptor 1'. Standard error is also usually attached to the terminal. It is designated 'file descriptor 2'.
+When you type a command such as cat, if you pass it no file name, it takes stdin from the keyboard. Try this: type cat RET, then some text, followed by CTL-D. As you'll see, cat takes its input from the keyboard and spews it to the terminal. If you type cat some_file, you are redirecting cat's stdin from the file, some_file. You should recollect my showing you the < operator. It is a redirection operator. Think of it as pointing from the source to the destination and as being pronounced 'comes from'. The < is implied by the last command, i.e., you could have equally well typed cat < some_file. What happens if you type cat > some_file? Think of this operator as the 'goes into' sign. It redirects the stdout of cat into the file, some_file. If some_file does not exist, it gets created; if it does, it gets overwritten. In order to append to some_file, you must type cat >> some_file.
+These three operators work for the terminal and for files. In order to redirect the stdout of a program ( think 'filter' ) to another program's stdin, you must use the pipe operator, |.
+Try this: type ls. Then, ls | sort. You might be keen to guess what sort does, but look at its man page to see what all it does ( this applies to any command that you use ). Now try this: ls | sort -r | head -n 5. If that does not impress you, su - to root ( always use su -l ) and type: cat /var/log/messages | grep root. Can you account for all the root logins? ( actually, if you have been rooted, you probably will find nothing obvious like that... ). Finally, try some things such as: cat /var/log/messages | grep $USER > $USER.log. Or, track down sound problems with: cat /var/log/messages | grep sound | unique > sound.msg... Experiment.
+A final note. You can use the file descriptors in order to redirect I/O. E.g., type find /var. That will give you a list of as many files as you can access ( do this as a regular user ). Suppose that you do not want to see the error messages. Type find /var 2> /dev/null > files_i_can_read. The descriptor '1' is presumed before the last goesinto. /dev/null is the bit bucket. Don't forget to empty it when you are done. Once you get the hang of redirection and learn some useful filters, you will be amazed at what you can do and will begin to wonder why anyone would want to use a graphical interface...
+== Control Characters ==
+There are a number of control characters that you should be familiar with: ^z, ^c, and ^d ( the carat ( ^ ) is a common symbol for the control key ). The ^z sequence sends a suspend signal to the terminal's controlling process. The ^c sequence sends an interrupt to the process, and ^d is the End of File ( EOF ) character that is used to terminate text strings and files ( which are really long text strings in UNIX, remember... ).
+== Environment Variables ==
+The shell maintains a set of variables that it and programs running under it can use to get information. The information represents the program's environment. The variables determine things such as the owner's user id ( UID ), name ( USER ), group id ( GID ), home directory ( HOME ), most recent command ( _ ), present working directory ( PWD ), etc. etc. Some programs might need special environment variables set, for example, in order for them to know where they are installed in the filesystem. E.g., some systems need MOZILLA_HOME set. If you use Java, you probably had to set JAVA_HOME to point to the directory where Java was installed or CLASSPATH to tell it where to find Java executables.
+Environment variables can be used to affect the behavior of a program be specifying a default set of arguments that you will not need to type at the command line. Bash uses them to determine things such as the number of columns to print on screen and what to display in the prompt. The most important variable, is the PATH. It is a colon-separated list of filesystem paths that the shell uses to determine where to look for execuatables given at the command line. If the command is not in the PATH, you need to specify the path absolutely. Try typing $ dhcpcd as a regular user. Bash will complain 'command not found'. Then type whereis dhcpcd. Notice that the path, /sbin is not in your PATH ( you can see the value of an environment variable by typing echo $VAR, where VAR is the variable you want to examine ).
+You can set a variable at the command line by typing VAR=value, where VAR is the name of the variable ( conventionally capitalized ) and value is whatever you need it to be -- note that if there are spaces in the value you will need to double-quote it. Try this: type CD=/mnt/cdrom. Now, type mount $CD. Your cdrom should mount if there is anything in it, or else produce an error message about no medium being found. Notice the $ before the variable, it is necessary whenever you use the variable, e.g., echo $CD, but not when you set it... Now, type bash then try using $CD to mount or umount the drive. It should fail. When you typed bash, you started another instance of the shell under the original one. It inherited an environment exported from its parent shell. Any variables that were not exported were not inherited. Now, type exit ( or CTL-d ) then export CD, then again bash. Try using $CD to mount the disc now. It should work. export with no arguments will return a list of exported variables. env will show all variables. It can also be used to run a command in an altered environment ( see the man page... ).
+== Job Control ==
+Job control provides a way for a user to stop, resume, or modify the priority of execution of running programs or to run more than one program from the same console. A 'job' in this context is an instance of a program in memory and running.
+A process can run in either the foreground or the background. A process that is running in the foreground is associated with the controlling terminal ( tty or pty ) and can receive keyboard events from the terminal. A background process is divorced from the terminal from which it was started and cannot receive terminal input.
+A process can be referred to in several ways. The Process ID number ( PID ) is one way. The job number is another. If you are referring to a process by job, you need to precede it by a % sign. In order to see what jobs are running on your terminal and the associated job numbers, type jobs. If you are logged into more than one terminal, type ps -ja ( the -j causes ps to use jobs' format ).
+In order to move a running job to the background, you need to suspend it. You do that by typing CTL-z . The job is then suspended and bash reports its job number on the command line. Type bg in order to resume the current ( suspended ) job in the background. You can specify a job, if you have more than one going, by using bg %job_no. You can resume a job in the foreground by typing %job_no or fg %job_no ( fg by itself resumes the current job ).
+We have covered kill elsewhere. Know that you can kill a process by its job number.
+Although it is not a shell builtin and is not technically 'job control', we will cover nice here. When a job is running, the kernel assigns time slices to it and other running processes in a 'fair' manner based on scheduling priority ( the kernel's scheduler is what determines who gets to run in what order and for how long ). If you want to change the 'weighting' that your program gets when the kernel allots slices, you can start it by typing nice -n command. The default nice level is 0. The highest priority is -19 and the lowest, 20. The higher the number, the 'nicer' the program is to others. The -n x is an optional specifier for the adjustment to the priority, where x is some number -- the default is +10 if not specified. You can use renice in order to change the priority of an already running process by typing renice priority PID. Only root can increase the priority of a process ( less nice ) and you can only renice processes that you own.
 == Globbing ==
  chown 701 public_html/chap{0{8,9},1{0,1,2}}
 the last token will be expanded to the list: chap08, chap09, chap10, chap11, and chap12 ( the command will attempt to operate on the all the paths, possibly failing on any path that does not exist ). Note that you can nest braces.
+=== Create Files From Words ===
+ touch fns.crud.{delete,update,insert,read}.{show,do}.php
+=== More Examples ===
+ for i in {1..99}; do echo 00{0..9} 0{10..99}; printf '|\n'; done
+ for i in {1..99}; do printf "%.3d " {8..10} ; printf '|\n'; done
+ for i in {1..99}; do echo {a..z}; printf '|\n'; done
+ for i in {1..99}; do echo {a..z}; echo -e '|'; done
+=== String Operations ===
+<TABLE
+BORDER="1"
+CLASS="CALSTABLE"
+><TR
+><TH
+ALIGN="LEFT"
+VALIGN="TOP"
+>Expression</TH
+><TH
+ALIGN="LEFT"
+VALIGN="TOP"
+>Meaning</TH
+></TR
+><TR
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+><TT
+CLASS="OPTION"
+>${#string}</TT
+></TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>Length of <TT
+CLASS="PARAMETER"
+><I
+>$string</I
+></TT
+></TD
+></TR
+><TR
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>&nbsp;</TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>&nbsp;</TD
+></TR
+><TR
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+><TT
+CLASS="OPTION"
+>${string:position}</TT
+></TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>Extract substring from <TT
+CLASS="PARAMETER"
+><I
+>$string</I
+></TT
+>
+		at <TT
+CLASS="PARAMETER"
+><I
+>$position</I
+></TT
+></TD
+></TR
+><TR
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+><TT
+CLASS="OPTION"
+>${string:position:length}</TT
+></TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>Extract <TT
+CLASS="PARAMETER"
+><I
+>$length</I
+></TT
+>
+		characters substring from <TT
+CLASS="PARAMETER"
+><I
+>$string</I
+></TT
+>
+		at <TT
+CLASS="PARAMETER"
+><I
+>$position</I
+></TT
+> [zero-indexed,
+		first character is at position 0]</TD
+></TR
+><TR
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>&nbsp;</TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>&nbsp;</TD
+></TR
+><TR
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+><TT
+CLASS="OPTION"
+>${string#substring}</TT
+></TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>Strip shortest match of
+	      <TT
+CLASS="PARAMETER"
+><I
+>$substring</I
+></TT
+> from front of
+	      <TT
+CLASS="PARAMETER"
+><I
+>$string</I
+></TT
+></TD
+></TR
+><TR
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+><TT
+CLASS="OPTION"
+>${string##substring}</TT
+></TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>Strip longest match of
+	      <TT
+CLASS="PARAMETER"
+><I
+>$substring</I
+></TT
+> from front of
+	      <TT
+CLASS="PARAMETER"
+><I
+>$string</I
+></TT
+></TD
+></TR
+><TR
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+><TT
+CLASS="OPTION"
+>${string%substring}</TT
+></TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>Strip shortest match of
+	      <TT
+CLASS="PARAMETER"
+><I
+>$substring</I
+></TT
+> from back of
+	      <TT
+CLASS="PARAMETER"
+><I
+>$string</I
+></TT
+></TD
+></TR
+><TR
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+><TT
+CLASS="OPTION"
+>${string%%substring}</TT
+></TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>Strip longest match of
+	      <TT
+CLASS="PARAMETER"
+><I
+>$substring</I
+></TT
+> from back of
+	      <TT
+CLASS="PARAMETER"
+><I
+>$string</I
+></TT
+></TD
+></TR
+><TR
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>&nbsp;</TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>&nbsp;</TD
+></TR
+><TR
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+><TT
+CLASS="OPTION"
+>${string/substring/replacement}</TT
+></TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>Replace first match of
+	      <TT
+CLASS="PARAMETER"
+><I
+>$substring</I
+></TT
+> with
+	      <TT
+CLASS="PARAMETER"
+><I
+>$replacement</I
+></TT
+></TD
+></TR
+><TR
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+><TT
+CLASS="OPTION"
+>${string//substring/replacement}</TT
+></TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>Replace <EM
+>all</EM
+> matches of
+	      <TT
+CLASS="PARAMETER"
+><I
+>$substring</I
+></TT
+> with
+	      <TT
+CLASS="PARAMETER"
+><I
+>$replacement</I
+></TT
+></TD
+></TR
+><TR
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+><TT
+CLASS="OPTION"
+>${string/#substring/replacement}</TT
+></TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>If <TT
+CLASS="PARAMETER"
+><I
+>$substring</I
+></TT
+>
+	      matches <EM
+>front</EM
+> end of
+	      <TT
+CLASS="PARAMETER"
+><I
+>$string</I
+></TT
+>, substitute
+	      <TT
+CLASS="PARAMETER"
+><I
+>$replacement</I
+></TT
+> for
+	      <TT
+CLASS="PARAMETER"
+><I
+>$substring</I
+></TT
+></TD
+></TR
+><TR
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+><TT
+CLASS="OPTION"
+>${string/%substring/replacement}</TT
+></TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>If <TT
+CLASS="PARAMETER"
+><I
+>$substring</I
+></TT
+>
+	      matches <EM
+>back</EM
+> end of
+	      <TT
+CLASS="PARAMETER"
+><I
+>$string</I
+></TT
+>, substitute
+	      <TT
+CLASS="PARAMETER"
+><I
+>$replacement</I
+></TT
+> for
+	      <TT
+CLASS="PARAMETER"
+><I
+>$substring</I
+></TT
+></TD
+></TR
+><TR
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>&nbsp;</TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>&nbsp;</TD
+></TR
+><TR
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>&nbsp;</TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>&nbsp;</TD
+></TR
+><TR
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+><TT
+CLASS="OPTION"
+>expr match "$string" '$substring'</TT
+></TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>Length of matching <TT
+CLASS="PARAMETER"
+><I
+>$substring</I
+></TT
+>*
+	        at beginning of <TT
+CLASS="PARAMETER"
+><I
+>$string</I
+></TT
+></TD
+></TR
+><TR
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+><TT
+CLASS="OPTION"
+>expr "$string" : '$substring'</TT
+></TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>Length of matching <TT
+CLASS="PARAMETER"
+><I
+>$substring</I
+></TT
+>*
+	        at beginning of <TT
+CLASS="PARAMETER"
+><I
+>$string</I
+></TT
+></TD
+></TR
+><TR
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+><TT
+CLASS="OPTION"
+>expr index "$string" $substring</TT
+></TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>Numerical position in <TT
+CLASS="PARAMETER"
+><I
+>$string</I
+></TT
+>
+		of first character in <TT
+CLASS="PARAMETER"
+><I
+>$substring</I
+></TT
+>*
+		that matches [0 if no match, first character counts as
+		position 1]</TD
+></TR
+><TR
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+><TT
+CLASS="OPTION"
+>expr substr $string $position
+	        $length</TT
+></TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>Extract <TT
+CLASS="PARAMETER"
+><I
+>$length</I
+></TT
+> characters
+	        from <TT
+CLASS="PARAMETER"
+><I
+>$string</I
+></TT
+> starting at
+	        <TT
+CLASS="PARAMETER"
+><I
+>$position</I
+></TT
+> [0 if no match, first
+		character counts as position 1]</TD
+></TR
+><TR
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+><TT
+CLASS="OPTION"
+>expr match "$string"
+	        '\($substring\)'</TT
+></TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>Extract <TT
+CLASS="PARAMETER"
+><I
+>$substring</I
+></TT
+>*, searching
+	        from beginning of <TT
+CLASS="PARAMETER"
+><I
+>$string</I
+></TT
+></TD
+></TR
+><TR
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+><TT
+CLASS="OPTION"
+>expr "$string" :
+	        '\($substring\)'</TT
+></TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>Extract <TT
+CLASS="PARAMETER"
+><I
+>$substring</I
+></TT
+>* , searching
+	        from beginning of <TT
+CLASS="PARAMETER"
+><I
+>$string</I
+></TT
+></TD
+></TR
+><TR
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+><TT
+CLASS="OPTION"
+>expr match "$string"
+	        '.*\($substring\)'</TT
+></TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>Extract <TT
+CLASS="PARAMETER"
+><I
+>$substring</I
+></TT
+>*, searching
+	        from end of <TT
+CLASS="PARAMETER"
+><I
+>$string</I
+></TT
+></TD
+></TR
+><TR
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+><TT
+CLASS="OPTION"
+>expr "$string" :
+	        '.*\($substring\)'</TT
+></TD
+><TD
+ALIGN="LEFT"
+VALIGN="TOP"
+>Extract <TT
+CLASS="PARAMETER"
+><I
+>$substring</I
+></TT
+>*, searching
+	        from end of <TT
+CLASS="PARAMETER"
+><I
+>$string</I
+></TT
+></TD
+></TR
+></TABLE>
+'''Source:'''
+* http://tldp.org/LDP/abs/html/refcards.html#AEN22664
+* http://wiki.bash-hackers.org/syntax/expansion/brace
+= Exploits =
+== Shellshock - Sep. 2014 ==
+=== Scan for Apache Intrusions ===
+ grep -H "() {" /var/log/httpd/*_log
+=== Manual Patch - Fedora Core 15 ===
+Check for Vulnerability
+'''Safe'''
+ env x='() { :;}; echo Server is vulnerable' bash -c "echo"
+ bash: warning: x: ignoring function definition attempt
+ bash: error importing function definition for `x'
+'''Vulnerable'''
+ env x='() { :;}; echo Server is vulnerable' bash.old -c "echo"
+ Server is vulnerable
+Check CPU Type
+ lscpu
+<pre>
+Architecture:          i686
+CPU op-mode(s):        32-bit, 64-bit
+Byte Order:            Little Endian
+CPU(s):                1
+On-line CPU(s) list:   0
+Thread(s) per core:    1
+Core(s) per socket:    1
+CPU socket(s):         1
+Vendor ID:             AuthenticAMD
+CPU family:            15
+Model:                 44
+Stepping:              2
+CPU MHz:               1808.328
+BogoMIPS:              3616.65
+L1d cache:             64K
+L1i cache:             64K
+L2 cache:              128K
+</pre>
+Check Kernel Type
+ uname -m
+ i686
+Check LONG_BIT
+ getconf LONG_BIT
+Locate Bash
+ which bash
+ /bin/bash
+Backup Bash
+ cp /bin/bash /bin/bash.old
+Determine Bash Version
+ bash --version
+ GNU bash, version 4.2.49(1)-release (i686-pc-linux-gnu)
+Setup Patch Working Directory
+ mkdir /usr/local/src/bashfix
+ cd /usr/local/src/bashfix
+Install Build Tools
+ sudo yum install patch ybacc bison autoconf
+Download Bash
+ wget https://ftp.gnu.org/pub/gnu/bash/bash-4.2.tar.gz
+ tar zxvf bash-4.2.tar.gz
+ cd bash-4.0
+Download and Apply Patches
+'''bash-multipatch.sh Script'''
+<pre>
+#!/bin/sh
+# A quick script file for downloading an applying multiple patches when manually compiling GNU bash on Linux
+# Written (mostly) by Steve Cook with (a little) help from Steve Jenkins
+# This really seems like a lame way to have to do this, but it works. :) Use at your own risk.
+# You can edit these variables
+version="4.2"
+nodotversion="42"
+lastpatch="49"
+# You probably don't want to edit anything below this line
+for i in `seq 1 $lastpatch`;
+do
+number=$(printf %02d $i)
+file="https://ftp.gnu.org/pub/gnu/bash/bash-${version}-patches/bash${nodotversion}-0$number"
+echo $file
+curl $file | patch -p0
+done
+</pre>
+Run Script
+ chmod 755 bash-multipatch.sh
+ ./bash-multipatch.sh
+Change Permissions
+ chown -R user:user bashfix/
+Change to Normal User
+ su user
+Run Configure
+ ./configure
+Run Make
+ make
+Run Make Tests
+ make test
+Check for New Bash Binary
+ ls -la bash
+ -rwxrwxr-x 1 user user 2362608 27. Sep 16:01 bash
+Replace Bash Binary
+ sudo cp -f bash /bin/bash
+Reset Bash
+ /bin/bash
+Retest
+ env x='() { :;}; echo Server is vulnerable' bash -c "echo"
+ bash: warning: x: ignoring function definition attempt
+ bash: error importing function definition for `x'
+Reboot Server
+ reboot
+= See Also =
+* [[Bash Scripts]] - Example Scripts
+= Sources =
+* Wayne M Albert
+* http://stevejenkins.com/blog/2014/09/how-to-manually-update-bash-to-patch-shellshock-bug-on-older-fedora-based-systems/
 [[Category:Linux]]
 [[Category:Mac OS X]]

Expression	Meaning
`${#string}`	Length of `$string`

`${string:position}`	Extract substring from `$string` at `$position`
`${string:position:length}`	Extract `$length` characters substring from `$string` at `$position` [zero-indexed, first character is at position 0]

`${string#substring}`	Strip shortest match of `$substring` from front of `$string`
`${string##substring}`	Strip longest match of `$substring` from front of `$string`
`${string%substring}`	Strip shortest match of `$substring` from back of `$string`
`${string%%substring}`	Strip longest match of `$substring` from back of `$string`

`${string/substring/replacement}`	Replace first match of `$substring` with `$replacement`
`${string//substring/replacement}`	Replace all matches of `$substring` with `$replacement`
`${string/#substring/replacement}`	If `$substring` matches front end of `$string`, substitute `$replacement` for `$substring`
`${string/%substring/replacement}`	If `$substring` matches back end of `$string`, substitute `$replacement` for `$substring`


`expr match "$string" '$substring'`	Length of matching `$substring`* at beginning of `$string`
`expr "$string" : '$substring'`	Length of matching `$substring`* at beginning of `$string`
`expr index "$string" $substring`	Numerical position in `$string` of first character in `$substring`* that matches [0 if no match, first character counts as position 1]
`expr substr $string $position $length`	Extract `$length` characters from `$string` starting at `$position` [0 if no match, first character counts as position 1]
`expr match "$string" '\($substring\)'`	Extract `$substring`*, searching from beginning of `$string`
`expr "$string" : '\($substring\)'`	Extract `$substring`* , searching from beginning of `$string`
`expr match "$string" '.*\($substring\)'`	Extract `$substring`*, searching from end of `$string`
`expr "$string" : '.*\($substring\)'`	Extract `$substring`*, searching from end of `$string`

Bash

From Luke Jackson

Current revision

Contents

Shells

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Dots

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Start Up

Profile

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Brace Expansion

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Shellshock - Sep. 2014

Scan for Apache Intrusions

Manual Patch - Fedora Core 15

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