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![Getting Help for Shell Builtins
• Type: type [-afptP] name [name…]
• For each NAME, indicate how it would be interpreted if used as a command
name.
• Help: help [-s] [pattern …]
• Display helpful information about builtin commands](https://image.slidesharecdn.com/linuxshellscripting2-221213122258-2ef72a0c/75/Linux-Shell-Scripting-pptx-6-2048.jpg)
![The if statement
• if [[ COMMANDS ]]
then
COMMANDS
else
COMMANDS
fi](https://image.slidesharecdn.com/linuxshellscripting2-221213122258-2ef72a0c/75/Linux-Shell-Scripting-pptx-10-2048.jpg)
![Sanity Checking
if [[ “${UID}” –ne 0 ]]
then
echo ‘Please run as root.’ >&2
exit 1
fi](https://image.slidesharecdn.com/linuxshellscripting2-221213122258-2ef72a0c/75/Linux-Shell-Scripting-pptx-12-2048.jpg)
![The for Loop
for VARIABLE in LIST
do
COMMANDS
done
The while Loop
while [[ COMMANDS ]]
do
COMMANDS
done](https://image.slidesharecdn.com/linuxshellscripting2-221213122258-2ef72a0c/75/Linux-Shell-Scripting-pptx-16-2048.jpg)
Linux Shell Scripting.pptx
- 1.
- 2. Vagrant • Vagrant boxadd ‘USER/BOX • vagrant box add jasonc/centos7 Will download iso(s) from vagrant public • mkdir testbox01 • cd testbox01 • vagrant init jasonc/centos7 • vagrant up • Vagrant ssh • Vagrant halt • Vagrant status • etc
- 3. The Shell ScriptFile • Naming shell scripts and file extension • Shell script file permissions • Chmod 755 script • Chmod +x script
- 4. Scripts • Sharp bang •#!/bin/bash • Comments • # • Variables • VAR=“value”
- 5. Creating Standard Outputand Quoting • The echo builtin • Single versus double quotes • “${VAR} gets expanded” • ‘${VAR} not expand’
- 6. Getting Help forShell Builtins • Type: type [-afptP] name [name…] • For each NAME, indicate how it would be interpreted if used as a command name. • Help: help [-s] [pattern …] • Display helpful information about builtin commands
- 7. Getting Help forLinux Commands • Man – format and display the on-line manual pages
- 8. Shell Variables • Theshell sets several variables automatically • HOSTNAME RANDOM UID …
- 9. Command Substitution • VAR=$(command) •VAR=`command` # Old style _________________________________________ • Echo “Output of command: $(command)”
- 10. The if statement •if [[ COMMANDS ]] then COMMANDS else COMMANDS fi
- 11. Exit Statuses • 0= true/ successful • 1=false/unsuccessful • Any non-zero exit status represents a failure • Exit 1 • Echo ${?} # you can also use $? • $? Will store the last exit status value.
- 12. Sanity Checking if [[“${UID}” –ne 0 ]] then echo ‘Please run as root.’ >&2 exit 1 fi
- 13. Obtaining Standard Input •The read shell builtin. • Read –p “A prompt: ” VARIABLE_ readonly VERBOSE=‘true’ Is like const where this variable cannot be reassigned any value.
- 14. Generating Random Data •The $RANDOM shell variable Echo ${RANDOM} Seemingly random data using checksums. date +%s%N | sha256sum | head -c8
- 15. Positional parameters • Argumentsvs Parameters • $0 = Stores the script name. • $1 = Stores the first argument • $2= Stores the second argument • $* = When used in quotes: “$1 $2 ….” • $@ = When used in quotes “$1” “$2”… • $# = total number of positions parameters • For var in “$@” • Do • Echo “$var” • Done • _____________ • ./test.sh 1 2 ‘3 4’ • 1 • 2 • 3 4 • ______________ • Now change “$@” to “$*” • 1 • 2 • 3 • 4
- 16. The for Loop forVARIABLE in LIST do COMMANDS done The while Loop while [[ COMMANDS ]] do COMMANDS done
- 17. I/O Redirection -Pipes • Sending STDOUT as STDIN. Echo ${PWORD} | passwd –stdin ${USER_NAME} • String manipulation & data munging with pipes. echo ‘!@#$%^’ | fold –w1 | shuf | head -c1
- 18. File I/O Redirection •COMMAND > /path/to/file • COMMAND >> /path/to/file • COMMAND < /path/to/file • COMMAND 2> /path/to/file • COMMAND &> /path/to/file
- 19. I/O Redirection • COMMAND|& COMMAND: to redirect both standard output and standard error to command (output) • Head –n3 /etc/passwd /fakefile |& cat -n • COMMAND &> FILE: to redirect both standard output and standard error to fil • COMMAND < FILE • COMMAND >&2 • COMMAND > /dev/null
- 20. File descriptors • 0stdin • 1 stdout • 2 stderr
- 21. Case statements • Case“${1}” in • start) echo ‘starting’ ;; • Stop) echo ‘stopping’;; • Status) echo ‘status’ ;; • *) • Echo ‘supply a valid option’ >&2 • Exit 1 • ;; • esac
- 22. Functions • Usage(){ • Echo“hello $1” • } • Usage “world”
- 23. Cut and Awk •Cut takes single character as delimiter however awk is more flexible • $echo “abc def” | cut –f 2 –d “ ” • Def • ___________ • $echo “abc def” | cut –f 2 –d “ ” • $echo “ abc def” | cut –f 2 –d “ ” • abc ______________________ $ echo "abc def" | awk '{ print $2 }' def $ echo "abc def" | awk '{ print $2 }' def $ echo " abc def" | awk '{ print $2 }' def
- 24. • Bar • Foo •Baz • ______________ • $cat test | sort • $sort < test • $sort test • ___________ • Bar • Baz • Foo Sort and Uniq To sort numerically use $sort –n test Uniq • $cat namelist1.txt • Jones, Bob • Smith, Mary • Babbage, Walter • $cat namelist2.txt • Jones, Bob • Jones, Shawn • Smith, Cathy • ___________________ • $sort namelist1.txt namelist2.txt | uniq • Babbage, Walter • Jones, Bob • Jones, Shawn • Smith, Cathy • Smith, Mary
- 25. -d on uniqwill output the duplicate line • $sort namelist1.txt namelist2.txt | uniq –d • Jones,bob -c on uniq will provide how many times it has found each entry • $sort namelist1.txt namelist2.txt | uniq –c • 1 Babbage, Walter • 2 Jones, Bob • 1 Jones, Shawn • 1 Smith, Cathy • 1 Smith, Mary