View source for Bash

= Bash Guide =

== Using Bash ==

Setting the default shell: http://www.unix.com/shell-programming-scripting/32664-how-change-default-shell-linux.html

[[Image:OSXTerminalSettings.png|none|250px|frame|You can set the default shell in Mac's Terminal by going settings and specifying the login shell.]]

== Startup Process ==

The order for sourcing dot files in bash is as follows:

'''Once per login session:'''

1. source /etc/profile - this contains the system-wide profile settings; these are only executed once per login session, and should define any bash variables that need to be defined for everyone; examples include the ${PATH}, the ${MANPATH}, the machine name, and/or enabling things that are not bash-specific (remember the [[Csh]] shell will also source .profile).

2. source ~/.profile - this contains user-specific profile settings; these settings are the same as above, except they are variables that should only be set for one user.  The user's ${PATH} and ${MANPATH} variables, in particular, should be set here.

See my [[dotprofile]]

3. source ~/.bash_profile - (?) This one I'm not so sure about, it's not a "standard" bash file to be sourced.  Plus its role is a little vague.  I use this to define settings for my bash history.

See my [[dotbash_profile]]

4. source /etc/bashrc - sources the system-wide bashrc file.  This will define the default appearance of the command prompt, any aliases, or any settings related to the bash history that should apply to every user.

5. source ~/.bashrc - sources the user-specific bashrc file.  This contains user-specific settings for the prompt, aliases, functions, etc.

See my [[dotbashrc]]

== Dot Files ==

= Bash Scripting =

== Looping ==

Looping in bash is really simple, and convenient - you can use other unix commands (most obviously "ls") to create lists, and then loop over each element of those lists.  For example, if I want to print out the name of every file in my home directory (granted, not very useful, but this is just an example), I can do this:

<source lang="bash">

for i in `/bin/ls -1 $HOME`; do
    echo $i
done

</source>

To do some serious bash looping kung-fu, check out [[Xargs]].

== Logical Operators ==

'''NOTE''': the use of double brackets for logical condition checks is highly recommended.

There are several logical operators available for checking conditions in bash.

These can be tested using a simple "if" statement.  In bash, if statements are of the form:

<source lang="bash">
if [[ condition ]]; then
    cmd
else
    cmd2
fi
</source>

The spaces between the brackets and the condition are essential.

===Integer Operators===

{|border="1"; class="wikitable"
!Operator
!Meaning
!Example

|-
|<code>-eq</code>
|returns true if arguments are equal
|<source lang="bash">
$ a=1; b=1; if [[ "$a" -eq "$b" ]]; then echo "true"; else echo "false"; fi
true

$ a=1; b=2; if [[ "$a" -eq "$b" ]]; then echo "true"; else echo "false"; fi
false
</source>

|-
|<code>-ne</code>
|returns true if arguments are not equal
|<source lang="bash">
$ a=1; b=1; if [[ "$a" -ne "$b" ]]; then echo "true"; else echo "false"; fi
false

$ a=1; b=2; if [[ "$a" -ne "$b" ]]; then echo "true"; else echo "false"; fi
true
</source>

|-
|<code>-gt</code>
|returns true if argument 1 is greater than argument 2
|<source lang="bash">
$ a=5; b=10; if [[ "$a" -gt "$b" ]]; then echo "true"; else echo "false"; fi
false
</source>

|-
|<code>-ge</code>
|returns true if argument 1 is greater than or equal to argument 2
|<source lang="bash">
$ a=15; b=10; if [[ "$a" -ge "$b" ]]; then echo "true"; else echo "false"; fi
true

$ a=10; b=10; if [[ "$a" -ge "$b" ]]; then echo "true"; else echo "false"; fi
true
</source>

|-
|<code>-lt</code>
|returns true if argument 1 less than argument 2
|<source lang="bash">
$ a=5; b=10; if [[ "$a" -lt "$b" ]]; then echo "true"; else echo "false"; fi
true
</source>

|-
|<code>-le</code>
|returns true if argument 1 less than or equal to argument 2
|<source lang="bash">
$ a=15; b=10; if [[ "$a" -le "$b" ]]; then echo "true"; else echo "false"; fi
false

$ a=10; b=10; if [[ "$a" -le "$b" ]]; then echo "true"; else echo "false"; fi
true
</source>

|-
|<code> \< </code>
|returns true if argument 1 less than argument 2

this needs to be escaped with a \ if it occurs inside single brackets; otherwise it can appear between double bracket or between double parentheses
|<source lang="bash">
$ a=10; b=10; if [ "$a" \< "$b" ]; then echo "true"; else echo "false"; fi
false

$ a=10; b=10; if [[ "$a" < "$b" ]]; then echo "true"; else echo "false"; fi
false

$ a=10; b=10; if (( "$a" < "$b" )); then echo "true"; else echo "false"; fi
false
</source>

|-
|<code> <= </code>
|returns true if argument 1 less than or equal to argument 2

this operator needs to go inside double parentheses
|<source lang="bash">
$ a=10; b=10; if (( "$a" <= "$b" )); then echo "true"; else echo "false"; fi
true
</source>

|-
|<code> > </code>
|returns true if argument 1 greater than argument 2

this needs to be escaped with a \ if it occurs inside single brackets; otherwise it can appear between double bracket or between double parentheses
|<source lang="bash">
$ z=10; zz=1000; 

$ if [ zz \> z ]; then echo "true"; else echo "false"; fi
true

$ if [[ zz > z ]]; then echo "true"; else echo "false"; fi
true
</source>

|-
|<code> >= </code>
|returns true if argument 1 greater than or equal to argument 2

this operator needs to go inside double parentheses
|<source lang="bash">
$ a=50; b=10; if (( $a >= $b )); then echo "true"; else echo "false"; fi
true
</source>

|}

===String Operators===

{|border="1"; class="wikitable"
!Operator
!Meaning
!Example

|-
|<code>=</code>
|returns true if two strings are equal
|<source lang="bash">
$ a=foo; b=foo; if [[ "$a" = "$b" ]]; then echo "true"; else echo "false"; fi
true

$ a=foo; b=bar; if [[ "$a" = "$b" ]]; then echo "true"; else echo "false"; fi
false
</source>

|-
|<code>==</code>
|returns true if two strings are equal; equivalent to <code>=</code>
|<source lang="bash">
$ a=foo; b=foo; if [[ "$a" == "$b" ]]; then echo "true"; else echo "false"; fi
true

$ a=foo; b=bar; if [[ "$a" == "$b" ]]; then echo "true"; else echo "false"; fi
false
</source>

Note the difference between quoting a string and not quoting a string:

<pre>
[[ $a ==  b*  ]] # returns true if $a starts with b (pattern matching)
[[ $a == "b*" ]] # returns true if $a is literally equal to b* (literal matching)
</pre>

|-
|<code>!=</code>
|returns true if strings are not equal
|<source lang="bash">
$ a=foo; b=bar; if [[ "$a" != "$b" ]]; then echo "true"; else echo "false"; fi
true
</source>

|-
|<code> < </code>
|returns true if argument 1 is less than (alphabetically) argument 2; capitals come before non-capitals
|<source lang="bash">
$ a=foo; b=bar; if [[ "$a" < "$b" ]]; then echo "true"; else echo "false"; fi
false

$ a=Foo; b=bar; if [[ "$a" < "$b" ]]; then echo "true"; else echo "false"; fi
true

$ a=bar; b=foo; if [[ "$a" < "$b" ]]; then echo "true"; else echo "false"; fi
true
</source>

|-
|<code> > </code>
|returns true if argument 1 is greater than (alphabetically) argument 2; capitals come before non-capitals
|<source lang="bash">
$ a=foo; b=bar; if [[ "$a" > "$b" ]]; then echo "true"; else echo "false"; fi
true

$ a=Foo; b=bar; if [[ "$a" > "$b" ]]; then echo "true"; else echo "false"; fi
false
</source>

|-
|<code>-z</code>
|returns true if the string is null
|<source lang="bash">
$ a=""; b="foobar"; if [ -z "$a" ]; then echo "true"; else echo "false"; fi
true

$ a=""; b="foobar"; if [ -z "$b" ]; then echo "true"; else echo "false"; fi
false
</source>

|-
|<code>-n</code>
|returns true if the string is NOT null
|<source lang="bash">
$ a=""; b="foobar"; if [ -n "$a" ]; then echo "true"; else echo "false"; fi
false

$ a=""; b="foobar"; if [ -n "$b" ]; then echo "true"; else echo "false"; fi
true
</source>

|}


===Compound Operators===

You can combine logical operators using and/or operators:

{|border="1"; class="wikitable"
!Operator
!Meaning
!Example

|-
|<code>-a</code>
|Logical and (both conditions must be true for condition to be true)
|<source lang="bash">
if [ "$expr1" -a "$expr2" ]
then
  echo "Both expr1 and expr2 are true."
else
  echo "Either expr1 or expr2 is false."
fi
</source>

|-
|<code>-o</code>
|Logical or (either condition must be true for condition to be true)
|<source lang="bash">
if [ "$expr1" -o "$expr2" ]
then
  echo "Either expr1 or expr2 is true."
else
  echo "Both expr1 and expr2 are false."
fi
</source>

|}

== Basic Math Operators ==

{{Main|Bash Math#Basic Math}}

== Complex Math Operators ==

{{Main|Bash Math#Operators}}

=Bash Keyboard Shortcuts=

==Editing Shortcuts==

The following are keyboard shortcuts for easy navigation/editing of commands that are on the Bash command line.

===Movement===

* '''C-a''' - Move to beginning of line
* '''C-e''' - Move to end of line



* '''M-f''' - Move forward 1 word
* '''M-b''' - Move backward 1 word



* '''C-f''' - Move forward 1 character
* '''C-b''' - Move backward 1 character

===Cutting and Pasting===

* '''C-k''' - kill (cut) from cursor to end of line
* '''C-w''' - kill (cut) from cursor to previous whitespace
* '''C-y''' - yank (paste) previously killed text at cursor

===Uncategorized===

* '''C-L''' - clear screen, reprint current line at top
* '''C-u''' - undo last edit
* '''C-d''' - delete character under cursor

= References =

Floating point math in the shell:

http://www.novell.com/coolsolutions/tools/17043.html

Fast bash math:

http://www.bytemycode.com/snippets/snippet/350/

Bash script iterate through array of values

http://www.tech-recipes.com/rx/636/bash-shell-script-iterate-through-array-values/

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