====== #!/bin/bash ======

  * [[csh]]
  * [[ksh]]
  * [[sh]]
  * [[tcsh]]
  * [[zsh]]

  * [[bash Built-In Commands]]
  * [[bash completion]]
  * [[bsfl]]
  * [[getopts]]
  * [[iterm]]

  * [[ftp://ftp.gnu.org/gnu/bash/]]
  * [[ftp://ftp.beandog.org/rsyncd/dotfiles/.bashrc.extra]] - My cross-platform ''.bashrc.extra'' :D
  * [[http://www.aboutlinux.info/2005/10/10-seconds-guide-to-bash-shell.html|Bash Shell Scripting - 10 Seconds Guide]]
  * [[http://tille.garrels.be/training/bash/ch07.html|Conditional statements]]
  * [[http://hacktux.com/bash/colors|bash colors]]
  * [[http://wiki.bash-hackers.org/doku.php|Bash Hackers wiki]]
  * [[http://www.commandlinefu.com/commands/browse|commandlinefu.com]]
  * [[http://www.mcsr.olemiss.edu/unixhelp/shell/oview1.1.html|Summary of shell facilities]]
  * [[http://ss64.com/bash/|An A-Z Index of the Bash command line for Linux]]
  * [[http://www.cheatography.com/oguzkonya/cheat-sheets/bash/|bash Cheat Sheet]] - some pretty advanced stuff
  * [[http://www.cyberciti.biz/faq/linux-bash-delete-all-files-in-directory-except-few/|Delete All Files In Directory Except Few]]
  * [[https://shellshocker.net/|Shellshocker]]
  * [[http://redsymbol.net/articles/unofficial-bash-strict-mode/|Use the Unofficial Bash Strict Mode (Unless You Looove Debugging)]] - strict mode to help find bugs
  * [[http://ascii-table.com/ansi-escape-sequences-vt-100.php|ANSI Escape Sequences]]
  * [[https://mywiki.wooledge.org/BashPitfalls|Bash Pitfalls]]

== String Operators ==
 
  * **-a** and
  * **-o** or
  * **=** or **==** equal to
  * **-n** string is not null
  * **-z** string is null, that is, has zero length

== Numeric Operators ==

  * **-eq** number equals
  * **-ne** number does not equal
  * **-gt** greater than
  * **-ge** greater than or equal to
  * **-lt** less than
  * **-le** less than or equal to

== File Operators ==

  * **-e** file exists (returns false in Bourne shell if file is a symlink)
  * **-f** file is not a directory or device file
  * **-d** file exists and is a directory
  * **-h** file exists and is a symlink (also **-L**)
  * **-s** file exists and has a size greater than zero
  * **-w** file exists and is writeable
  * **-x** file exists and is executable
  * **-r** file exists and is readable
  * **-b** file is a block device
  * **-c** file is a character device
  * **-p** file is a pipe
  * **-S** file is a socket
  * **-O** you are owner of file
  * **-G** you are group owner of file

== Regular Expressions ==

Use ''=~'' followed by a regular expression pattern.  **Do not** enclose the pattern in quotes if using in a ''test'' block.

Check if a variable is a positive integer:

<code>
[[ $1 =~ ^[0-9]+$ ]]
</code>

== Functions ==

Functions are created and called the same as any shell script: use command line arguments as parameters to pass, and echo any output.

<code bash>
function parse_input() {
   INPUT=$1
   echo "You passed ${1} as an argument"
}
</code>

== Read each line ==

<code bash>
cat filename | while read line; do
  echo "Your line says ${line}"
done
</code>

== String subset ==

Syntax: ${variable:<starting integer>[:<num characters>]}

<code bash>
string="O hai"
echo ${string:2} # returns hai
</code>

== Strings ==

** Get string length **

<code bash>
${#string}
expr length $string
</code>

** Find the index of the first occurrence of a letter in a string **

Returns 0 on not found.

<code bash>
expr index abcdefg d
</code>

** Strings as commands **

You need to use ''eval'' to **reparse** a command through bash.

See [[http://fvue.nl/wiki/Bash:_Why_use_eval_with_variable_expansion|here]]

<code bash>
#!/bin/bash
cmd="date --date=\"1 days ago\""
$cmd         # Doesn't work
eval $cmd    # Works
</code>

** Simple sed replacement **

<code bash>
echo testing testing2 | sed -e 's/ /\|/' # returns testing|testing2
</code>

** Simple cut with a delimiter, grabbing a field **

<code bash>
eix --only-names -Ie bash | cut -d "/" -f 2
</code>

== Variables ==

  * [[http://www.tldp.org/LDP/Bash-Beginners-Guide/html/sect_03_02.html]]

  * **$#** - number of bash arguments
  * **$*** - display all variables passed
  * **$$** - pid of shell, or script being run
  * **$0** - name of the script
  * **$!** - pid of last job run in background
  * **$_** - last command run, without the arguments

== Displaying variables ==

When setting a variable using the backtick operator, use double quotes around the variable to retain newlines.

<code bash>
files=`ls`
echo "$files"
</code>

== Console settings ==

Get the size of the available cols, lines.  Useful when writing shell applications that display output that needs to be paged:

<code>
tput cols
tput lines
</code>

== Cool bash stuff ==

  * **mktemp** (coreutils) make a temporary file in /tmp

== Get exit status from piped outputs ==

"Wonder piping!" --Shaine

<code bash>
$ true | false | true
$ echo ${PIPESTATUS[*]}
</code>

== Special variables ==

  * ''$#'' Number of arguments on commandline.
  * ''$?'' Exit status of last command.
  * ''$$'' Process id of current program.
  * ''$!'' Process id of last backgroundjob or background function.
  * ''$0'' Program name including the path if started from another directory.
  * ''$1..n'' Commandline arguments, each at a time.
  * ''$*'' All commandline arguments in one string.

== Colors ==

^ Color ^ Normal ^ Bold ^
| Gray | 00;38 | 01;30 |
| Black | 00;30	| |
| Red |00;31 | 01;31 |
| Green | 00;32 | 01;32 |
| Purple 1 | 00;33 | 01;33 |
| Blue | 00;34 | 01;34 |
| Purple 2 | 00;35 | 01;35 |
| Cyan | 00;36 | 01;36 |
| White | 00;37 | 01;38 |
| Bright Blue | | 01;37 |
| Yellow | 02;33 | |
| Dark Gray | | |

== Trapping signals ==

You can use ''trap'' to capture a signal, such as Ctl-C to kill a command, and then map it to an internal function inside the bash script.

This is useful in scenarios where a shell script calls other scripts, and cancelling them would only cancel that one executed script instead of the main one.

<code>
control_c() {
        exit 1
}

trap control_c INT
</code>

== Command Line Control ==

  * Delete: Ctrl W
  * Clear Line: Ctrl U
  * Start of Line: Ctrl A
  * End of Line: Ctrl E

== Check Input ==

Check to see if input is an integer:

<code>
if [[ $1 == ?(-)+([0-9]) ]]; then echo "$1 is an integer"; fi
</code>