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Bash Scripting

About this document

This document is a reference and guide for creating and running basic bash scripts. It assumes a knowlege of basic terminal usage.

Useful links

Basic understanding

  • <command> [-opt1[ -opt2]] [<arg1>[, <arg2>]] (one single command, many possible options, many possible arguments)
  • scripts can run from any directory if...
    • a) the script is located in a directory in your PATH variable, or
    • b) you run the script with the full path to it's location
  • add scripts to ~/bin so they are in your PATH
  • make scripts executable using chmod +x <scriptname>
  • debug scripts with bash -x
  • check which directories are in your PATH: echo $PATH
  • if executable shell programs have the same name but are in different directories the program in the first directory in your path is run
  • name your scripts with a .sh extension

Create and execute a script

$ cd ~/bin
$ nano myscript.sh # opens nano to create a new file

< # start of file contents on next line
#!/bin/bash # the 'hash-bang' tells the shell that the command interpreter should be 'bash' (execute using the program found at /bin/bash)
MYGREETING="Hello, "
if [[ $USER = Rion ]]
then echo $MYGREETING "Rion"
else echo $MYGREETING "whoever you are"
fi
> # end of file contents, control+x to exit nano (y to save)

$ ls -l # by default the file is not exectuable
$ chmod +x myscript.sh # gives file global executable permissions
$ ls -l # check to see permissions (should be x's in each of user/group/everyone fields now)
$ cd ~ # go back home
$ myscript # executes script, would need ./myscript if running from ~/bin

Create custom commands (aliases)

$ alias
$ alias ls='ls --color -l'
$ alias # lists curent aliases (both global and in current session)

Edit .bash_profile

Your .bash_profile file controls how your bash terminal session looks and operates. Changes made to this file will persist configuration changes to all subsequent terminal sessions.

$ cd ~/
$ nano .bash_profile

# edit the file with custom aliases, custom variables, and/or custom scrips, for example
echo "custom aliases:"
echo "'code' -> 'cd ~/code'"
echo "'ls' -> 'ls -la'"
alias code="cd ~/code"
alias ls="ls -la"
MYVARIABLE="Here is some text that will show in the terminal window upon open"
echo $MYVARIABLE # display the variable
# save and close file

$ [ctrl+t] # opens a new tab

see here to compare .bashrc vs. .bash_profile files