This document provides an overview of basic commands and concepts for using the Bash shell on Linux and Mac terminals. It covers common commands for navigation, files, processes, variables, control flow, and functions. Key points include using man pages, aliases and tab autocomplete for help; piping and chaining commands; conditional statements and loops; and writing Bash scripts and configuration files. Hands-on tutorials are recommended for learning Bash scripting.

1. Productive Bash
Getting Comfortable Scripting on the Command Line

2. Command Line Basics
● Terminal:
○ command line interface application
● Shell:
○ command line interpreter that runs in terminal
● Why use the command line terminal?
○ fast
○ less memory intensive than GUI tools
○ simple, efficient on remote hosts
■ display host not needed
○ versatile set of built in commands
○ custom commands with scripts

3. Command Help
● Command help
○ man pages (or info)
■ command, function, system call (usually C) lookup
○ help
■ list built in commands
■ describe a built in command
○ type
■ reports type (shell builtin, keyword, file etc.)
○ alias
■ make command shortcuts
● alias ll=”ls -la”
■ simplify command and flag combinations
○ tab autocomplete
○ ↑↓ through command history

4. Command History
● history
○ command etc. history list with line numbers
● !n
○ repeat from history by line number
● !-i
○ repeat ith previous command
● !!
○ repeat last command
○ same as !-1
● chain commands
○ command1 ; command2
○ command1 && command2
○ command1 || command2

5. Jobs and Processes
● Process:
○ executing program
○ unique process id (PID) and name
○ ps
■ list all currently executing processes
● Job:
○ one or more related processes
○ job number
○ job spec (%n)
○ jobs
■ list all jobs running in background
● &
○ run in background

6. Job Control
● CTRL-C
○ terminate process
● CTRL-Z
○ suspend process
● bg
○ restart suspended job, send to background
○ job spec %n optional
● fg
○ send job to foreground
○ job spec %n optional
● kill
○ terminate or signal process by process id
● killall
○ terminate or signal process by process name

7. Shell Environment
● env
○ set and print environment variables
● printenv
○ print environment variables
● export
○ declare and set variable
● unset
○ delete variable
● which
○ find program in environment $PATH

8. File System Commands
● file
○ tests and reports file type (directory, ASCII, executable etc.)
● ls
○ list directory contents
● cd
○ change directory
● rm
○ remove a file or directory
● ln
○ link to file or directory
○ symbolic link (-s flag)
■ can link directories
■ can cross filesystems

9. File System Commands
● chmod
○ change file or directory permissions
● mkdir
○ create a directory
● find
○ search directory
■ find . -name “*.py”
■ find A B -name “*.bak” -exec rm {} ;
● grep
○ search file contents
■ grep -i copyright *.py
■ grep -Rn 201[5-7] .
● diff
○ compare 2 or more files line by line

10. File System Commands
● touch
○ changes file modification & access time, create empty file
● cat
○ read files, output to stdout
● more/less
○ page through text
○ less allows backward paging
● head
○ display first n lines or bytes of a file (default n=10 lines)
● tail
○ display last n lines or bytes of a file (default n=10 lines)

11. File System Commands
● uniq
○ filter and/or report repeated lines in file
● sort
○ sort lines in file
● wc
○ count words, lines, characters and bytes in files
● sed
○ stream, edit and substitute text patterns using regular expressions in files
○ sed -e 's/foo/bar/g' -i.sed test.txt
● cut
○ cut portions from file by delimiter (default is tab), byte or character position
○ writes to standard output

12. Chaining Commands
● pipe:
aylas-mbp-4:masters ayla$ git status --porcelain
M paper.tex
?? arch.key
?? arch2.key
?? images/arch2/
?? paper.tex.save.1
?? vol.key
aylas-mbp-4:masters ayla$ git status --porcelain | grep "^??" | cut -d ' ' -f 2
arch.key
arch2.key
images/arch2/
paper.tex.save.1
vol.key

13. Chaining Commands
● xargs:
○ build and execute commands from standard input
○ print directory file on 1 line
■ ls | xargs echo
aylas-mbp-4:masters ayla$ find . -name "*.tex" | xargs -t wc -w
wc -w ./outline.tex ./paper.tex
491 ./outline.tex
1936 ./paper.tex
2427 total

14. Bash Script Variables
● Variables
○ string, integers, arrays etc.
○ no native floating point math
■ use builtin tools instead (bc: arbitrary precision calculator language)
○ readonly
○ declare
■ limit type (array, integer)
■ can make variables readonly
■ declare [option flag] [variable[=value] ...]
● Positional parameters
○ $*: quoted string containing positional parameters
○ $@: array of positional parameters
○ $0, $1,…: parameter variables
○ $#: number of arguments

15. Bash Control Flow
● Conditional statements:
○ if test -f $1; then echo “File $1 exists”; fi
○ if [ -f $1 ]; then echo “File $1 exists”; fi
○ if [[ -f $1 ]]; then echo “File $1 exists”; fi
if [[ $i -lt 0 ]] && (( $i % 2 == 0 ))
then
echo “$i is negative and even”
elif [[ $i -ge 0 ]]
then
if (( $i % 2 == 0 ))
then
echo "$i is positive and even"
else
echo "$i is positive and odd"
fi
else
echo “$i is negative and odd”
fi

16. Bash Control Flow
● case statements
case "$1" in
start)
start
;;
stop)
stop
;;
status)
status anacron
;;
*)
echo $"Usage: $0 {start|stop|status}"
exit 1
esac
http://tldp.org/LDP/Bash-Beginners-Guide/html/sect_07_03.html

17. Bash Control Flow
● for loops:
○ for ((i=1; i<=10; i+=2)); do echo “Loop $i times”; done
○ for i in {1..5}; do …; done
○ for i in $(seq 1 5); do …; done
for file in $filelist
do
echo $file
done

18. Bash Control Flow
● while loops:
○ while [[ $i -lt 4 ]]; do echo $i; i=$(($i+1)); done
while true
do
if [[ $i -lt 4 ]]; then
break
fi
i=$(($i+1))
done

19. Bash Operators
● Integer comparison
○ in [[ ]] and [ ]: -gt, -ge, -lt, -le, -eq, -ne
○ in (( )): <, <=, >, >=, ==, !=
● String comparison
○ ==, !=
○ in ASCII alphabetical order: >, <
○ -z (null string), -n (not null)
○ also file test operators (-e, -f, -d etc.)
● Boolean
○ in [[ ]]: &&, ||, !
○ in [ ] and with test: -a, -o, !
● Math
○ in (( )): +, -, *, / (rounds to integer), ++, --, %, +=, *=, /=, -=, %=

20. Parameters and Strings
● Parameter manipulation
○ parameter length
■ ${#parameter}
○ remove pattern from end
■ ${parameter%pattern} or ${parameter%%pattern}
■ list=*.tiff; for l in $list; do convert "$l" "${l%.tiff}.png"; done
○ remove pattern from beginning
■ ${parameter#pattern} or ${parameter##pattern}
○ substitute first matched pattern
■ ${parameter/pattern/replacement}
○ substitute all matched pattern
■ ${parameter//pattern/replacement}
● String concatenation
○ $a$b
○ foo$a
○ substrings (length optional)
■ ${parameter:offset:length}
https://www.ibm.com/developerworks/library/l-bash-parameters/

21. Bash Functions
● basic syntax:
function simple
{
myvariable=“foo”
}
simple
echo $myvariable

22. Bash Functions
● positional parameters:
○ same as scripts
● no return value to caller
● local vs global variables:
○ myvariable visible in function block
function simple_with_arg
{
local myvariable=$1
echo $myvariable
}
simple_with_arg "foo"

23. Bash Scripts
● shell setup
○ #!/usr/bin/env bash
● list of commands, or commands and functions
● run with executable permissions or using source command
● command execution, substitution
○ backtick: `mycommand`, output=`mycommand`
○ subshell (preferred)
■ (mycommand), output=$(mycommand)
■ (mycommand1; mycommand2; mycommand3 ...)
■ python_files=$(ls -l $(find . -name "*.py"))
#!/bin/bash
OF=/var/my-backup-$(date +%Y%m%d).tgz
tar -cZf $OF /home/me/

24. Bash Configuration Scripts
● .bash_profile
○ executed on login shell startup
○ always executed for new Mac OS X terminal windows and tabs
● .bashrc
○ executed on interactive non-login shells
http://www.joshstaiger.org/archives/2005/07/bash_profile_vs.html

25. Useful, hands-on bash tutorials...
● https://www.hackerrank.com/domains/shell/bash
● https://www.ibm.com/developerworks/library/l-bash
● http://www.hackmac.org/articles/bash/bash-101-hello-world-and-a-little-further
● http://ryanstutorials.net/bash-scripting-tutorial
● https://en.wikibooks.org/wiki/Bash_Shell_Scripting