Shell Script

A Shell Script is a system-level control program which enables certain operations to be automated.

Shebang

The "shebang" or "opening header" is a directive which should appear at the top of a particular type of Shell script and location. It should be any ONE of the following:

#!/bin/sh
#!/bin/bash
#!/usr/bin/perl
#!/usr/bin/tcl
#!/bin/sed -f
#!/usr/awk -f

Commands

run

./program.sh [ARGS]

Run shell script As root:

sudo sh program.sh [ARGS]

locate

locate <something>

ex:

locate tomcat

list all known files/folders which contain the name "tomcat"

grep

ps ax | grep <something>

ex:

ps ax | grep VRD

list running processes which start with "VRD"

nohup

nohup <something>

ex:

nohup VRD-proxy &

run VRD-Proxy application with "no hang-ups" (even after shell closes)

trap

Setup a cleanup function to be triggered upon script exit:

 __cleanup ()
 {
    -f "MyProcess.lock"  && rm "MyProcess.lock"
 }
 # ...
 # bunch of other commands and stuff
 # ...
 trap __cleanup EXIT

Environment Variables

• How to set environment variable for everyone under my linux system?: https://stackoverflow.com/questions/1641477/how-to-set-environment-variable-for-everyone-under-my-linux-system (some techs say to put it in "/etc/environment" others say "/etc/profile.d/" and yet more say "~/.bashrc" as an environment variable)
• How To Read and Set Environmental and Shell Variables on a Linux VPS: https://www.digitalocean.com/community/tutorials/how-to-read-and-set-environmental-and-shell-variables-on-a-linux-vps

Resources

• Short but Simple Shell Script cheat-sheet: http://www.cheat-sheets.org/saved-copy/shellcheatsheet.pdf
• Bash Shell Scripting Cheat Sheet: http://riceball.com/d/content/shell-scripting-cheat-sheet
• Shell Scripting - Syntax Cheat Sheet: http://steve-parker.org/sh/cheatsheet.pdf
• Advanced Shell Scripting guide: http://www.linuxtopia.org/online_books/advanced_bash_scripting_guide/refcards.html
• Shellshock - Better 'bash' shell security patches now available: http://www.zdnet.com/shellshock-better-bash-patches-now-available-7000034115/
• Bash Guide for Beginners: http://tldp.org/LDP/Bash-Beginners-Guide/html/index.html
• Advanced Bash-Scripting Guide: http://www.tldp.org/LDP/abs/html/ (An in-depth exploration of the art of shell scripting)
• Shelldorado: http://shelldorado.com/ (UNIX shell scripting resource)
• Bash Scripting examples: http://programmingexamples.wikidot.com/bash-scripting

Tutorials

• Writing Shell Database and File Backup Scripts for OS X: http://www.noendpress.com/vroman/shellscripting/index.php
• Basic sample shell script: http://www.go2linux.org/starting-with-shell-script
• UNIX & Linux Shell Scripting Tutorial: http://www.dreamsyssoft.com/sp_ifelse.jsp
• Unix / Linux - Using Shell Variables: https://www.tutorialspoint.com/unix/unix-using-variables.htm
• Working with Variables in Shell Scripts: http://www.informit.com/articles/article.aspx?p=29246
• Working with script variables, including command line arguments: http://pangea.stanford.edu/computerinfo/unix/programming/shell/variables.html
• How to Pass Arguments to Shell Script: http://bashscript.blogspot.com/2009/11/how-to-pass-arguments-to-shell-script.html
• Shell Script to get user input: http://www.thelinuxblog.com/shell-script-get-user-input/
• Handling Command Line Arguments: http://www.shelldorado.com/goodcoding/cmdargs.html
• How do you take a single line of input from the user in a shell script?: http://www.cyberciti.biz/faq/read-input-from-the-user-in-a-shell-script/
• How to set a variable to the output from a command in Bash?: https://stackoverflow.com/questions/4651437/how-to-set-a-variable-to-the-output-from-a-command-in-bash
• Set shell script Variable to output of command: https://stackoverflow.com/questions/38641757/set-shell-script-variable-to-output-of-command
• How do I trim leading and trailing whitespace from each line of some output?: https://unix.stackexchange.com/questions/102008/how-do-i-trim-leading-and-trailing-whitespace-from-each-line-of-some-output
• CURL used in shell: https://superuser.com/questions/760645/curl-used-in-shell (checking for status to ensure program closes correctly)
• Shell Script - syntax error near unexpected token `else': https://unix.stackexchange.com/questions/87776/shell-script-syntax-error-near-unexpected-token-else (you must either put "if [ ... ]; then" for same-line or newline between the "if [ ... ]" and "then")
• How To Untar a Tarball .tar or .tar.gz File In Linux Shell Command: http://www.wallpaperama.com/disp-post26.html
• I/O With Files That Aren't Files: http://java.dzone.com/articles/io-files-arent-files (using PIPEs to temporarily open/cache files and streams for processing)
• Passing arguments to a shell script: http://osr507doc.sco.com/en/OSUserG/_Passing_to_shell_script.html
• Passing named arguments to shell scripts: https://unix.stackexchange.com/questions/129391/passing-named-arguments-to-shell-scripts
• Jenkins shell script does not receive the new value of a job parameter: https://stackoverflow.com/questions/35085788/jenkins-shell-script-does-not-receive-the-new-value-of-a-job-parameter
• Bash -- Exit and cleanup on error: https://stackoverflow.com/questions/36335186/bash-exit-and-cleanup-on-error
• How to run a shell script at startup: https://stackoverflow.com/questions/12973777/how-to-run-a-shell-script-at-startup
• How to save the output of a shell command to a variable: https://samindaw.wordpress.com/2009/02/25/how-to-save-the-output-of-a-shell-command-to-a-variable/
• How to increment a variable in bash?: https://askubuntu.com/questions/385528/how-to-increment-a-variable-in-bash
• HowTo -- Check If a String Exists: https://www.shellhacks.com/check-if-string-exists/
• Bash – Check If Two Strings are Equal: https://tecadmin.net/tutorial/bash/examples/check-if-two-strings-are-equal/
• How to represent multiple conditions in a shell if statement?: https://stackoverflow.com/questions/3826425/how-to-represent-multiple-conditions-in-a-shell-if-statement
• How do I make a batch file terminate upon encountering an error?: https://stackoverflow.com/questions/734598/how-do-i-make-a-batch-file-terminate-upon-encountering-an-error/8965092#8965092
• How to Use "Case Statements" in Bash Scripts: https://www.howtogeek.com/766978/how-to-use-case-statements-in-bash-scripts/
• How to Use Brace Expansion in Linux’s Bash Shell: https://www.howtogeek.com/725657/how-to-use-brace-expansion-in-linuxs-bash-shell/
• How to check if a string contains a substring in Bash: https://stackoverflow.com/questions/229551/how-to-check-if-a-string-contains-a-substring-in-bash
• Split string into array (on delimiter) Shellscript: https://stackoverflow.com/questions/10130280/split-string-into-array-shellscript
• How to find the length of an array in shell?: https://stackoverflow.com/questions/1886374/how-to-find-the-length-of-an-array-in-shell
• Bash split string into array using 4 simple methods: https://www.golinuxcloud.com/bash-split-string-into-array-linux/

External Links

• wikipedia: Shell script
• wikipedia: Bash (Unix shell)
• wikipedia: Comparison of command shells
• Bash Guide for Beginners: http://tldp.org/LDP/Bash-Beginners-Guide/html/
• An example of Shell Scripting using the Simpson family: http://www.joedog.org/articles-cheat-sheet/
• Advanced Bash-Scripting Guide -- An in-depth exploration of the art of shell scripting: http://www.tldp.org/LDP/abs/html/
• Rute (terminal) User's Tutorial and Exposition: http://rute.2038bug.com/index.html.gz
• "/bin/sh : bad interpreter: No such file or directory": https://www.raspberrypi.org/forums/viewtopic.php?t=77127 (likely requires a run through "dos2unix" CLI tool if you edited it in Windows and are trying to run in Linux/Unix)
• Gracefully Close an Application from the Command Line in Mac OS X: http://osxdaily.com/2014/09/05/gracefully-quit-application-command-line/
• How to kill a script running in terminal, without closing terminal (Ctrl + C doesn't work)?: https://askubuntu.com/questions/520107/how-to-kill-a-script-running-in-terminal-without-closing-terminal-ctrl-c-doe
• Exit terminal after running a bash script: https://askubuntu.com/questions/611648/exit-terminal-after-running-a-bash-script
• How do I exit or cancel a bad bash command?: https://unix.stackexchange.com/questions/45646/how-do-i-exit-or-cancel-a-bad-bash-command
• Bash script exit cleanup: https://stackoverflow.com/questions/24151726/bash-script-exit-cleanup
• An introduction to services, runlevels, and rc.d scripts: https://www.linux.com/news/introduction-services-runlevels-and-rcd-scripts
• How to run a shell script at startup: https://stackoverflow.com/questions/12973777/how-to-run-a-shell-script-at-startup
• Run shell script on startup or boot: https://askubuntu.com/questions/108800/run-shell-script-on-startup-or-boot
• How to execute a shell script on startup?: https://superuser.com/questions/126106/how-to-execute-a-shell-script-on-startup
• Looping through the content of a file in Bash?: https://stackoverflow.com/questions/1521462/looping-through-the-content-of-a-file-in-bash
• Loop through an array of strings in Bash?: https://stackoverflow.com/questions/8880603/loop-through-an-array-of-strings-in-bash
• Redirect stderr and stdout in Bash: https://stackoverflow.com/questions/637827/redirect-stderr-and-stdout-in-bash

See Also

MySQL | FTP | Cloud Computing | Batch Script | TCL