Introduction to the Bash Shell

• Bourne-Again SHell (reference manual)
• Provides extensive command line and scripting functionality
• Available on UNIX-based platforms (including Linux and MacOS X)
• Available under Windows using Cygwin

online man pages

The first place to get information on any external command (program) used in bash is to use the switch --help on the program:

user@host:~> program --help

user@host:~> man program

man 1 mkdir
man 2 mkdir
man 1 printf
man 3 printf

1   Executable programs or shell commands
2   System calls (functions provided by the kernel)
3   Library calls (functions within program libraries)
4   Special files (usually found in /dev)
5   File formats and conventions eg /etc/passwd
6   Games
7   Miscellaneous (including macro packages and conventions), e.g. man(7), groff(7)
8   System administration commands (usually only for root)
9   Kernel routines [Non standard]

man -k mkdir

mkdir (1)            - make directories
mkdir (2)            - create a directory
mkdirat (2)          - create a directory relative to a directory file descriptor

help <built-in command>

help cd
help type
help help

$ type cd
$ cd is a shell builtin

$ type diff
$ diff is /usr/bin/diff

$ type ls
$ ls is aliased to `ls --color=auto'

$ type dir
$ dir is aliased to `ls -l --color --group-directories-first'

$ type foo
$ bash: type: foo: not found

$ type sudo
$ sudo is hashed (/usr/bin/sudo)

The shaded commands are external commands. All others are internal, although some can be both.

bash Command	Similar Windows Command	Description
chmod	attrib.exe	Change a file's mode (attributes)
cat	type	Display a text file (also concatenates files)
cd	cd	Change directory
clear	cls	Clears the screen
cp	copy	Copy files
date	date/time	Read/set the system date and time
echo*	echo	Print to the screen
for	for	Looping construct
if	if	Conditional construct
less	more.com	Display one page of text at a time.
ls	dir	List files
man	help.exe	Displays the man (manual) page for a given command
mkdir	mkdir/md	Create (make) a new directory
mv	move/rename	Move and/or rename files
popd	popd	Pop most recent directory and change to it
pushd	pushd	Save current directory and change
rm	del	Removes (deletes) a file
rmdir	rmdir/rd	Removes (deletes) a directory

Command	Description
alias	Create an alias (shortcut) for a command
cal	Display a calendar to the screen (text)
chown	Change owner and group of a file
dd	Data dump, raw read/write for files and devices
diff	Display differences between files
du	Calculate disk usage
file	Determine a files type
find	Search for files matching certain criteria
grep	Search files for lines matching specified text
head	Display first few lines in a file
history	Display command history
kill*	Send a signal to a process
ln	Create a link between files
ps	List processes and status
pwd*	Print current working directory
tail	Show last few lines of a file
time*	Measure the running time of a program (External command as well)
type	Determine the type of a command (e.g. file, alias, keyword, built-in, etc.)
wc	Prints count of lines, words, and bytes
which	Shows where a program is in the file system

To create a PDF from the man pages, use this command (showing chmod as an example):

man -t chmod > chmod.ps && ps2pdf chmod.ps && rm chmod.ps

#!/bin/bash

if [[ $# -eq 0 ]]; then
  echo "Usage: man2pdf topic"
  exit
fi

man -t $1 > $1.ps && ps2pdf $1.ps && rm $1.ps

chmod +x man2pdf.sh

Redirection, Piping and Filters (Review)

Recall from CS 120:

• To redirect input from a file to a program, use the < operator. (Example: prog < input.txt)
• To redirect output from a program to a file, use the > operator. (Example: prog > output.txt)
• To append output to a file (instead of overwrite the file), use the >> operator. (Example: prog >> output.txt)
• To connect stdout of a one program to stdin of another program, use the | operator. (Example: prog1 | prog2)
• You can mix and match these operators. (Example: prog1 < input.txt | prog2 > output.txt)

Here's a couple of very simple examples that show how filters work. We'll use this file: Declaration of Independence without word-wrap. There are actually 9 lines in the file, and 4 of them are empty.

• Counting lines, words, and characters with the wc filter:

  cat doi-nowrap.txt | wc

  Output:

  9     664    3980    

• Wrapping lines to 60 characters using the fmt filter:

  cat doi-nowrap.txt | fmt -w 60 > doi-wrap60.txt

  Output file: doi-wrap60.txt

• Wrapping lines to 60 characters and adding line numbers with the nl filter:

  cat doi-nowrap.txt | fmt -w 60 | nl -ba > doi-wrap60-nl.txt

  Output file: doi-wrap60-nl.txt

• This chain of commands displays all of the IP address of the computer except the localhost address (127.0.0.1):

  $ ifconfig | grep "inet addr" | grep -v "127.0.0.1" | cut -c 21- | cut -d' ' -f1 | sort -n
  

The same thing reading from a file instead. Assume we did this:

$ ifconfig > ip.txt

Now we can get the input from the file ip.txt:

$ grep "inet addr" < ip.txt | grep -v "127.0.0.1" | cut -c 21- | cut -d' ' -f1 | sort -n

or

$ cat ip.txt | grep "inet addr" | grep -v "127.0.0.1" | cut -c 21- | cut -d' ' -f1 | sort -n

• Here is an example for a Windows XP computer with 4 IP addresses: ip.txt (You'll have to modify the command for Windows 7 because the format of the output has changed.) I want to find out what class B networks are setup on the computer:

  $ cat ip.txt | grep "IP Address" | cut -c 45- | cut -d. -f1,2 | sort | uniq
  

  The output is:

  10.10
  192.168
  

• If I just wanted the count, instead of the addresses, I would just pipe it all to wc:

  $ cat ip.txt | grep "IP Address" | cut -c 45- | cut -d. -f1,2 | sort | uniq | wc -l
  

  The output is:

  2
  

If we break it down one pipe at a time, we will see how this all works.
1. First, we extract only the lines that contain the string IP Address using the grep filter:

   $ cat ip.txt | grep "IP Address"
   

   The output is (there are 8 leading spaces, shown with dots ········ to the left):

   ········IP Address. . . . . . . . . . . . : 192.168.17.1
   ········IP Address. . . . . . . . . . . . : 192.168.13.1
   ········IP Address. . . . . . . . . . . . : 10.10.32.67
   ········IP Address. . . . . . . . . . . . : 192.168.56.1
   

2. Next, we extract only the characters from position 45 until the end of the line, using the cut filter:

   $ cat ip.txt | grep "IP Address" | cut -c 45-
   

   The output is:

   192.168.17.1
   192.168.13.1
   10.10.32.67
   192.168.56.1
   

3. Then, we extract the first 2 fields of the string using cut again, specifying the period as the field delimiter:

   $ cat ip.txt | grep "IP Address" | cut -c 45- | cut -d. -f1,2 
   

   The output is:

   192.168
   192.168
   10.10
   192.168
   

4. Now, sort the output using the sort filter:

   $ cat ip.txt | grep "IP Address" | cut -c 45- | cut -d. -f1,2 | sort 
   

   The output is:

   10.10
   192.168
   192.168
   192.168
   

5. To remove duplicates, we use the uniq filter (input must be sorted, hence the previous step):

   $ cat ip.txt | grep "IP Address" | cut -c 45- | cut -d. -f1,2 | sort | uniq
   

   The output is:

   10.10
   192.168
   

6. Finally, we send the output to the wc filter (word count) specifying we just want the line count:

   $ cat ip.txt | grep "IP Address" | cut -c 45- | cut -d. -f1,2 | sort | uniq | wc -l
   

   The output is:

   2
   

   All of the filters are configurable via command line options:
   • cat --help
   • grep --help
   • cut --help
   • sort --help
   • uniq --help
   • wc --help

   By the way, the script above to create PDF documents from the man pages could have been done using pipes:

   man -t grep | ps2pdf - > grep.pdf
   

   And that, boys and girls, is what makes the command line indispensible for the experienced user. Imagine if you had to write a C/C++ program to do this; it would be quite lengthy. (It's not just the parsing, but you'd have to figure out a system-independent way to query the system for IP addresses, etc.)

One of the best things you can do as a student learning the power of computers is to learn the filters in /usr/bin. There are hundreds and learning all of them is unlikely. However, you only really need to learn a couple of dozen to make your computing significantly more productive.

Over time, you will find yourself spending more and more time at the command line because it enables you to do things that are impossible in a GUI. Also, before you sit down to write a program in C or C++ to do some kind of system work, find out if there is a program or set of filters that will do what you want. Most likely, there is, or at least you may only need to write another filter to complete the task.

Writing Your Own Filters

FILE *infile

initialize counters;

IF filename given on command line
  infile = open file for read/text
  (Handle errors)
ELSE
  infile = stdin;
END IF
  
WHILE not end of file
  read a character
  inc char_counter
  IF this is the first char read or the previous character is a newline
    print line number
    inc line_counter
  END IF
  print the character that was read
  set prev char to character read
END WHILE

IF not reading from stdin
  close file
END IF

Simple bash Programming

• Redirection (>, >>, <, 2>)
• Pipes (|)
• Multiple commands (; && ||)
• Background processes/forking (&)
• Iteration (for, while, until)
• Conditionals (if, case)
• Functions (function)
• Testing file types and variable values (test, [])
• Command substitution (assign the output of a command/program/function to a variable)

Variables in bash:

• Variable values are generally character strings
• Case sensitive
• Global unless using the local keyword
• let command used for arithmetic
• Values obtained using $var or ${var} (The second way is a little safer.)
• Special variables, e.g.: $PATH, $1, $2

• Can have any extension, but should have executable (x) privileges
• Comments begin with #
• First line should be #!/bin/bash
• Can use command line arguments

Arithmetic operations

Arithmetic in bash seems a little strange at first. Examples will illustrate.

Example 1 - Using the let command.

Code	Output	Description
a=1+2 echo $a let a=1+2 echo $a let a = 1 + 2 echo $a let a="1 + 2" echo $a	1+2 3 error 3	No arithmetic done. Verbatim assignment. The let command is for arithmetic. Can't have any spaces with let. Using quotes allows spaces.

Example 2 - Using (( )) for arithmetic context.

Code	Output	Description
a=1 ((a=$a+2)) echo $a ((a = a + 2)) echo $a ((a += 2)) echo $a	3 5 7	Set a to 1 Add 2 to a Same, but can use spaces and no $. Same.

Functions

• Basic syntax:

function_name() 
{ 
  command1...
  command2...
  ...
} 

Functions in bash do not specify parameters nor return type, although both are supported.
• Example 1 - No parameters, no return

Function	Calling it	Output
say_hello() { echo "Hello!" }	say_hello	Hello!

• Example 2 - passing parameters

Function	Calling it	Output
print3() { echo "Printing: $1 $2 $3" }	print3 apple banana cherry print3 apple "banana cherry" dog	apple banana cherry apple banana cherry dog

• Example 3 - returning a value

Function	Calling it	Output
count_files() { local count=`ls -l | wc -l` echo $count }	num_files=$(count_files) echo $num_files echo "The number of files is $(count_files)"	17 The number of files is 17

• Example 4 - passing parameters and returning a value

Function	Calling it	Output
multiply() { local product=$(($1 * $2)) echo $product }	total=$(multiply 3 5) echo $total	15

• Exit codes - Functions can use the return command, but it's only for integers between 0 and 255.

Conditionals

• There are if Statements.
• Block-style if: (if and then must be on separate lines)
• This is the CS 180 style:

 if CONDITION-COMMANDS
 then
   COMMAND(S)...
 elif CONDITION-COMMANDS   # optional
 then
   COMMAND(S)...
 else            # optional
   COMMAND(S)...
 fi              # required

• if and then on one line needs semicolons:

if CONDITION-COMMANDS; then COMMAND(S)...; fi

• Example 1 - simple arithmetic comparison. (The space around the square brackets: [[ and ]] is required.)

Code	Output
value=3 if [[ $value -eq 3 ]]; then echo "The value is 3" else echo "The value is NOT 3" fi	The value is 3

• Arithmetic comparison operators

Bash operator
Equivalent
C operator
Meaning
-eq
=
equal
-ne
!=
not equal
-lt
<
less
-gt
>
greater
-le
<=
less or equal
-ge
>=
greater or equal

• Example 2 - string comparison

Code	Output
string1="Hello" string2="hello" if [[ $string1 == $string2 ]]; then echo "Same strings" else echo "Different strings" fi	Different strings

• String comparison operators

Operator
Meaning
==
equal
!=
not equal
<
less
>
greater

• Example 3 - simple file test (See more file tests.)

Code	Output
filename="foo.txt" echo -n "$filename " if [[ -e $filename ]]; then echo "exists" else echo "does not exist" fi	foo.txt does not exist

• Example 4 - Calling a function (Function checks to see if the file is executable and returns true or false)

validate()
{
  if [[ -x $1 ]]; then
    true
  else
    false
  fi
}

Code	Output
filename="a.out" echo -n "$filename " if validate $filename; then echo "is executable" else echo "is not executable" fi	a.out is executable

What's the deal with the single and the double brackets? ([ ] vs. [[ ]]). The best answer I've found on the subject is here.

In a nutshell, [ ] is older and more portable, while [[ ]] is newer, easier to use, but doesn't work with all shells. Since we are talking about the bash shell, this will always work. By the way, there is actually a program in /usr/bin that is named [. That's right, do this:

ls -l /usr/bin/[

-rwxr-xr-x 1 root root 30,244 2011-02-23 05:22 /usr/bin/[

Iteration

There are for loops and while loops of course.

Block-style for loop (CS 180 style):

for arg in LIST
do 
  command(s)... 
done

One line needs semicolons:

for arg in LIST; do command(s)...; done

Example 1 - These all do the same thing

1	2	3	4
for a in 1 2 3 4 5 do echo -n "$a " done	NUMS="1 2 3 4 5" for a in $NUMS do echo -n "$a " done	for a in {1..5} do echo -n "$a " done	for ((a = 1; a <= 5; a++)) do echo -n "$a " done

Output:

1 2 3 4 5 

Note that these two lines mean different things:

for a in 1 2 3 4 5

for a in "1 2 3 4 5"

The first contains 5 separate items (numbers), but the second is a single item (a string). Notice in the second example above, the string "1 2 3 4 5" is assigned to a variable, NUMS, and that variable is used in the for loop.

Example 2 - This lists all of the .cpp files in the current directory

for a in *.cpp
do
  echo "$a "
done  

Example 3 - Calling a function in the for loop

generate_list()
{
  echo "one two three"
}

for word in $(generate_list)
do
  echo "$word"
done

Block-style while loop (CS 180 style):

while CONTROL-COMMAND
do 
  COMMAND(S)... 
done

One line needs semicolons:

while CONTROL-COMMAND; do COMMAND(S)...; done   

Example 4 - Block-style while loop example

i=0
while [ $i -lt 4 ]
do
  i=$(($i + 1))   # can also use ((i++))
  echo -n "$i "
done

Example 5 - Calling a function in the while loop

t=0
condition()
{
  ((t++))

  if [ $t -lt 5 ]
  then
    return 0  # true
  else
    return 1  # false
  fi
}

while condition
do
  echo "Still going: t = $t"
done

• Arrays
• To create an empty array:

list=()        

• Fill it with values:

num=5
for ((a = 0; a < num; a++))
do
  list[(($a))]=$a
done

• You can use +=:

num=5
for ((a = 0; a < num; a++))
do
  list+=($a)
done

• Iterate over it and print the values:

for ((a = 1; a < num; a++))
do
  echo ${list[a]}
done

• Another way to iterate and print:

for i in "${list[@]}"
do
  echo $i
done

• Command-line parameters:
• Parameters are separated by a space.
• Accessed by position: $1 $2 $3 $4 etc.
• Positions 10 and above: ${10} ${11} ${12} etc.
• The number of parameters is in the variable $#
• The command line in one string is the variable $@
• Parameters with spaces require double-quotes.
• Examples: Assume this is the command line: 1 2 3 "4 5 6" 7 8

Simple (no loop)	Loop with $@	Loop with "$@"	Loop with $*	Loop with "$*"
echo $# echo $@ echo $1 echo $2 echo $3 echo $4 echo $5 echo $6 Output: 6 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8	for a in $@ do echo $a done Output: 1 2 3 4 5 6 7 8	for a in "$@" do echo $a done Output: 1 2 3 4 5 6 7 8	for a in $* do echo $a done Output: 1 2 3 4 5 6 7 8	for a in "$*" do echo $a done Output: 1 2 3 4 5 6 7 8

• Other examples:

Loop with shift	Copy to an array	Printing the array elements	Another way to print
num=$# for ((a = 1; a <= num ; a++)) do echo $1 shift done Output: 1 2 3 4 5 6 7 8	list=() num=$# for ((a = 1; a <= num ; a++)) do list[(($a))]=$1 shift done	for ((a = 1; a <= num ; a++)) do echo ${list[a]} done Output: 1 2 3 4 5 6 7 8	for i in "${list[@]}" do echo $i done Output: 1 2 3 4 5 6 7 8

• Nice explanation is here.
• Executing commands and capturing output.
• Various ways to do it.
• Simple example using the date command:
• Typing date at the command prompt:

$ date

Output:

Thu May 24 10:21:40 PDT 2012

• In a bash script:

Command        Output
-----------------------------------------------------------
date           Thu May 24 10:24:11 PDT 2012
dt=$(date)
echo dt        dt
echo $dt       Thu May 24 10:24:11 PDT 2012
dt=`date`
echo $dt       Thu May 24 10:24:11 PDT 2012
$(date)        ./script3: line 42: Thu: command not found

bash_script used to produce all of the examples. It ain't pretty, but here it is. There are actually some lines in the script that aren't on this web page. Examples of looping over filenames in a directory.

This is an excellent place to start: Bash Guide for Beginners

A real world example that I use on student submissions.

Enhancing Your bash Experience

• Define aliases (abbreviations) for long commands
• Create lengthy scripts and functions for common tasks
• Customize the output color of many programs

Aliases

alias short_name='some_other_command'

alias dir='ls -l'
alias del='rm'
alias cp='cp --preserve=timestamps'

Example using the ls (list files) command:

Default ls command:

mmead@olga:~/digipen/cs180> ls BatchFiles.html ding.wav quiz_material Hotel California.mp3 dumpit.exe quiz_material.zip OperatingSystemConcepts8e.zip exams sandbox bash.odt foo.mmg spanish.txt batch graph-0.jpg start.wav batch.odt graph-1.jpg temp.html book makehelp.bat didcgaf-setup.txt new.css

ls using long listing (lowercase 'L': -l), and listing directories before files (--group-directories-first):

mmead@olga:~/digipen/cs180> ls -l --group-directories-first total 145,592,320 drwxr-xr-x 3 mmead mmead 4,096 2011-05-16 08:36 batch drwxr-xr-x 12 mmead mmead 4,096 2011-05-09 20:52 book drwxr-xr-x 2 mmead mmead 4,096 2011-05-18 19:29 exams drwxr-xr-x 2 mmead mmead 4,096 2011-05-09 21:11 quiz_material drwxr-xr-x 2 mmead mmead 4,096 2011-05-12 11:45 sandbox -rw-r--r-- 1 mmead mmead 14,188 2011-05-18 19:25 bash.odt -rw-r--r-- 1 mmead mmead 56,690 2011-05-15 20:39 BatchFiles.html -rw-r--r-- 1 mmead mmead 30,568 2011-05-15 11:52 batch.odt -rw------- 1 mmead mmead 3,480 2010-10-10 22:09 didcgaf-setup.txt -rwxr-xr-x 1 mmead mmead 80,856 2001-08-23 05:00 ding.wav -rw-r--r-- 1 mmead mmead 58,880 2011-05-10 20:19 dumpit.exe -rw-r--r-- 1 mmead mmead 0 2011-05-18 19:20 foo.mmg -rw-r--r-- 1 mmead mmead 25,932 2010-03-30 11:49 graph-0.jpg -rw-r--r-- 1 mmead mmead 25,679 2010-03-30 11:52 graph-1.jpg -rw------- 1 mmead mmead 6,533,037 2010-10-31 17:22 Hotel California.mp3 -rw-r--r-- 1 mmead mmead 4,291 2011-05-16 08:34 makehelp.bat -rw------- 1 mmead mmead 11,140 2011-04-20 12:58 new.css -rw-r--r-- 1 mmead mmead 138,465,681 2011-05-09 20:53 OperatingSystemConcepts8e.zip -rw-r--r-- 1 mmead mmead 52,876 2011-05-06 18:30 quiz_material.zip -rw-r--r-- 1 mmead mmead 153 2010-10-16 10:57 spanish.txt -rwxr-xr-x 1 mmead mmead 1,192 2001-08-23 05:00 start.wav -rw-r--r-- 1 mmead mmead 1,253 2011-05-18 19:33 temp.html

Same as above but enabling color output (--color):

mmead@olga:~/digipen/cs180> ls -l --group-directories-first --color=auto total 145,592,320 drwxr-xr-x 3 mmead mmead 4,096 2011-05-16 08:36 batch drwxr-xr-x 12 mmead mmead 4,096 2011-05-09 20:52 book drwxr-xr-x 2 mmead mmead 4,096 2011-05-18 19:29 exams drwxr-xr-x 2 mmead mmead 4,096 2011-05-09 21:11 quiz_material drwxr-xr-x 2 mmead mmead 4,096 2011-05-12 11:45 sandbox -rw-r--r-- 1 mmead mmead 14,188 2011-05-18 19:25 bash.odt -rw-r--r-- 1 mmead mmead 56,690 2011-05-15 20:39 BatchFiles.html -rw-r--r-- 1 mmead mmead 30,568 2011-05-15 11:52 batch.odt -rw------- 1 mmead mmead 3,480 2010-10-10 22:09 didcgaf-setup.txt -rwxr-xr-x 1 mmead mmead 80,856 2001-08-23 05:00 ding.wav -rw-r--r-- 1 mmead mmead 58,880 2011-05-10 20:19 dumpit.exe -rw-r--r-- 1 mmead mmead 0 2011-05-18 19:20 foo.mmg -rw-r--r-- 1 mmead mmead 25,932 2010-03-30 11:49 graph-0.jpg -rw-r--r-- 1 mmead mmead 25,679 2010-03-30 11:52 graph-1.jpg -rw------- 1 mmead mmead 6,533,037 2010-10-31 17:22 Hotel California.mp3 -rw-r--r-- 1 mmead mmead 4,291 2011-05-16 08:34 makehelp.bat -rw------- 1 mmead mmead 11,140 2011-04-20 12:58 new.css -rw-r--r-- 1 mmead mmead 138,465,681 2011-05-09 20:53 OperatingSystemConcepts8e.zip -rw-r--r-- 1 mmead mmead 52,876 2011-05-06 18:30 quiz_material.zip -rw-r--r-- 1 mmead mmead 153 2010-10-16 10:57 spanish.txt -rwxr-xr-x 1 mmead mmead 1,192 2001-08-23 05:00 start.wav -rw-r--r-- 1 mmead mmead 1,253 2011-05-18 19:33 temp.html

alias dir='ls -l --color --group-directories-first'

export BLOCK_SIZE=\'1

Changing the Command Prompt

1. First, by coloring the prompt, it is easy to find the commands in a sea of output. If all output is the same color as the prompt, it's very difficult to find the command.
2. Second, by using a different color prompt between "user" mode and "superuser" mode, it makes it less likely that you'll do something bad to your computer. (This isn't a cure for that and I'm not going to get into the whole philosophy of "when and why you should ever be root (administrator) while using the command line")
3. Most bash shells do automatic coloring today, but even a few years ago this wasn't done. That's why I did this. You may find that this is unecessary today. But, you still may want to change the colors to something you prefer.

   This is how you would do it:

export PS1="\[\033[1;33m\]\u@\h:\w>\[\033[0m\]"

# Assume that my user ID is 1234
# 33=yellow, 31=red, admin/root/superuser is 0
user_color()
{
  if [ "$UID" -eq "0" ]; then
    echo 31
  elif [ "$UID" -eq "1234" ]; then
    echo 33
  fi
}

export PS1="\[\033[\$(user_color)m\]\u@\h:\w>\[\033[0m\]" 

dircolors Abbreviations
fi = normal file di = directory ln = symbolic link pi = fifo pipe so = socket bd = block device cd = character device or = symbolic link to nonexistent file (orphan) mi = symbolic link pointing to non-existent file ex = executable

Color Codes	Color Codes (cont.)
00 = normal 01 = bold 04 = underlined 05 = blinking 07 = reversed 08 = concealed 31 = red 32 = green 33 = orange 34 = blue 35 = purple 36 = cyan 37 = grey 40 = black background 41 = red background 42 = green background 43 = orange background 44 = blue background 45 = purple background 46 = cyan background 47 = grey background	90 = dark grey 91 = light red 92 = light green 93 = yellow 94 = light blue 95 = light purple 96 = turquoise 100 = dark grey background 101 = light red background 102 = light green background 103 = yellow background 104 = light blue background 105 = light purple background 106 = turquoise background

See the man pages for dircolors and dir_colors

Colorize the Output from grep

# Add color to grep
export GREP_COLOR="44;37;01"
export GREP_OPTIONS="--color=auto"

$ grep -i "^a.*b.*c.*d.*" /usr/share/dict/american-english  

abdicated
abducted
abracadabra
abracadabra's
abscessed
abscond
absconded
absconding
absconds
abstracted
abstractedly

$ grep -i "^b.*s.*g.*d.*" /usr/share/dict/american-english  

besieged

Colorizing man Pages

# Add color to man pages
export LESS_TERMCAP_mb=$'\E[01;31m'      # begin blinking
export LESS_TERMCAP_md=$'\E[01;34m'      # begin bold
export LESS_TERMCAP_me=$'\E[0m'          # end mode
export LESS_TERMCAP_se=$'\E[0m'          # end standout-mode
export LESS_TERMCAP_so=$'\E[01;44;33m'   # begin standout-mode - info box
export LESS_TERMCAP_ue=$'\E[0m'          # end underline
export LESS_TERMCAP_us=$'\E[01;32m'      # begin underline

The bash shell has all of the modern shell features you would want.

Tab Completion

whereis chmod

chmod: /bin/chmod /usr/share/man/man1/chmod.1.gz /usr/share/man/man2/chmod.2.gz

whe<TAB>

whereis

If there is more than one command or file that will complete what you've typed, bash won't complete it because it's ambiguous. In this case, pressing the TAB key twice quickly, will show you a list of possible candidates. For example, typing this

wh<TAB><TAB>

whatis    whereis   which     while     whiptail  who       whoami    whois

Cycling Through the Command Completion

The alternative is to have the TAB key cycle through the choices. So, in the example above, typing TAB will first show whatis and pressing TAB a second time will show whereis. Pressing TAB will cycle through the choices. This is especially useful if the first several characters in a filename match (which is common). Suppose you had these two filenames in a directory:

filename-a.txt
filename-b.txt

To enable this cycling method, add this to your .bashrc file:

bind '"\t":menu-complete'

Navigating and Search Through the Command History

In this case, you want to search for that command. Let's say you ran this command 20 minutes ago:

valgrind -q --leak-check=full --show-reachable=yes --tool=memcheck ./memmgr 1 2

(reverse-i-search)`': 

But there's more! You don't have to type the first characters in the command. If you've used the valgrind command with dozens of different options, you'd have to cycle through all of them to find the one you want. If you pick something a little unique within the command line, it will jump to that one. For example, typing Ctrl-r and then the characters t o o will match the --tool=memcheck portion and show the entire command with that substring it it. Very, very cool!

Case-insensitive command completion

ls d<TAB>

ls Downloads

set completion-ignore-case on

Making the Changes Permanent

If the file exists, just open it with a text editor and add the lines at the bottom. If the file doesn't exist, it will be created. gedit is a decent text editor for new Linux users:

gedit ~/.bashrc

# Now, the dir command will display files properly :)
alias dir='ls -l --color --group-directories-first'

# Add color to grep output
export GREP_COLOR="44;37;01"
export GREP_OPTIONS="--color=auto"

# Add color to man pages
export LESS_TERMCAP_mb=$'\E[01;31m'      # begin blinking
export LESS_TERMCAP_md=$'\E[01;34m'      # begin bold
export LESS_TERMCAP_me=$'\E[0m'          # end mode
export LESS_TERMCAP_se=$'\E[0m'          # end standout-mode
export LESS_TERMCAP_so=$'\E[01;44;33m'   # begin standout-mode - info box
export LESS_TERMCAP_ue=$'\E[0m'          # end underline
export LESS_TERMCAP_us=$'\E[01;32m'      # begin underline

# This causes the TAB-completion to cycle through possible matches
bind '"\t":menu-complete'

# This causes commas to be inserted in numbers, e.g. 1234567890 becomes 1,234,567,890
export BLOCK_SIZE=\'1

Note: Simply modifying the .bashrc in your home directory will not cause the changes to take effect. If you want them to take effect immediately, you have to type this while in your home directory:

      source .bashrc

Now the changes are in effect only for the current shell. If you have other shells already open, you will have to type that command in each one. However, any new shells that you open up will have the changes.

Creating functions

lpath()
{
  perl -e 'print "\n";
  print join("\n", split(/:/, $ENV{'PATH'}));
  print "\n";'
}

lpath

echo $PATH | tr : '\n'

This example is more verbose. It will extract (unzip, untar, uncompress, etc.) a file based on the file's extension.

#------------------------------------------
#------Extraction of compressed files------
# from ARCH Wiki

extract() 
{
  if [ -f $1 ]; then
    case $1 in
        *.tar.bz2)   tar xvjf $1    ;;
        *.tar.gz)    tar xvzf $1    ;;
        *.bz2)       bunzip2 $1     ;;
        *.rar)       rar x $1       ;;
        *.gz)        gunzip $1      ;;
        *.tar)       tar xvf $1     ;;
        *.tbz2)      tar xvjf $1    ;;
        *.tgz)       tar xvzf $1    ;;
        *.zip)       unzip $1       ;;
        *.Z)         uncompress $1  ;;
        *.7z)        7z x $1        ;;
        *)           echo "don't know how to extract '$1'..." ;;
    esac
  else
    echo "'$1' is not a valid file!"
  fi
}

Global customization

• Bash Reference Manual
• Bash man page
• Bash FAQ
• Bash Pitfalls
• BASH Frequently Asked Questions
• Bash Hackers Wiki
• Bash shell scripting tutorial
• Advanced Bash-Scripting Guide
• Custom bash colorizing
• More bash customizations from Arch Wiki

• Lots of examples It appears to be a work in progress, but useful as it is.