/bash_scripts

Polishing Bash/Shell scripts

Primary LanguageShell

Victors-MacBook-Pro-2@zazvick: ~/Projects/personal/training/bash-scripts
$ ./tn test
Hello, World!
Victors-MacBook-Pro-2@zazvick: ~/Projects/personal/training/bash-scripts
$ ls
tn
Victors-MacBook-Pro-2@zazvick: ~/Projects/personal/training/bash-scripts
$ ./tn test
Hello, World!
Victors-MacBook-Pro-2@zazvick: ~/Projects/personal/training/bash-scripts
$ ls
notes.txt tn
Victors-MacBook-Pro-2@zazvick: ~/Projects/personal/training/bash-scripts
$ cat notes.txt
Tue Jan 16 01:28:22 CST 2018 : test
Victors-MacBook-Pro-2@zazvick: ~/Projects/personal/training/bash-scripts
$ ./tn working
Hello, World!
Victors-MacBook-Pro-2@zazvick: ~/Projects/personal/training/bash-scripts
$ cat notes.txt
Tue Jan 16 01:28:22 CST 2018 : test
Tue Jan 16 01:28:36 CST 2018 : working
Victors-MacBook-Pro-2@zazvick: ~/Projects/personal/training/bash-scripts
$ ls
notes.txt tn

Let's put a confirmation for user:

Victors-MacBook-Pro-2@zazvick: ~/Projects/personal/training/bash-scripts (master)
$ ./tn hello
Hello, World!
Note saved: hello

How to check if your bash script name is not reserved by bash:


# Use type

$ type test
test is a shell builtin
Victors-MacBook-Pro-2@zazvick: ~/Projects/personal/training/bash-scripts (master)
$ type cp
cp is /bin/cp
Victors-MacBook-Pro-2@zazvick: ~/Projects/personal/training/bash-scripts (master)
$ type foo
-bash: type: foo: not found
Victors-MacBook-Pro-2@zazvick: ~/Projects/personal/training/bash-scripts (master)
$ type bar
-bash: type: bar: not found
Victors-MacBook-Pro-2@zazvick: ~/Projects/personal/training/bash-scripts (master)

Recap:

Shell Script

- A file containing commands
- Executed by your shell

Naming your scripts

Don’t forget to set permissions

- chmod u+w

Shebang
 
- First line
- #!/bin/bash

Use comments

- Comments start with #

Add script to your PATH

- ./tn
- /home/zazvick/tn
- Tip: make a bin folder in your home
- PATH=“$PATH:~/bin”

Or call it with a full pathname

Variables

  • Variables

    • Create
    • Assign value
    • Use value

  • Variable Names

  • Good habits when using variables

Victors-MacBook-Pro-2@zazvick: ~/Projects/personal/training/bash-scripts (master)
$ greeting="hello"
Victors-MacBook-Pro-2@zazvick: ~/Projects/personal/training/bash-scripts (master)
$ $greeting
-bash: hello: command not found
Victors-MacBook-Pro-2@zazvick: ~/Projects/personal/training/bash-scripts (master)
$ echo $greeting
hello
Victors-MacBook-Pro-2@zazvick: ~/Projects/personal/training/bash-scripts (master)
$ filename="somefile.txt"
Victors-MacBook-Pro-2@zazvick: ~/Projects/personal/training/bash-scripts (master)
$ touch $filename
Victors-MacBook-Pro-2@zazvick: ~/Projects/personal/training/bash-scripts (master)
$ ls
notes.txt    readme.md    somefile.txt tn
Victors-MacBook-Pro-2@zazvick: ~/Projects/personal/training/bash-scripts (master)
$ files="file1 file2"
Victors-MacBook-Pro-2@zazvick: ~/Projects/personal/training/bash-scripts (master)
$ touch $files
Victors-MacBook-Pro-2@zazvick: ~/Projects/personal/training/bash-scripts (master)
$ ls -l files
ls: files: No such file or directory
Victors-MacBook-Pro-2@zazvick: ~/Projects/personal/training/bash-scripts (master)
$ ls -l $files
-rw-r--r--  1 zazvick  staff  0 Jan 16 23:49 file1
-rw-r--r--  1 zazvick  staff  0 Jan 16 23:49 file2
Victors-MacBook-Pro-2@zazvick: ~/Projects/personal/training/bash-scripts (master)
$ echo $greeting, $USER
hello, zazvick
Victors-MacBook-Pro-2@zazvick: ~/Projects/personal/training/bash-scripts (master)
$ echo $greeting, $user
hello,
Victors-MacBook-Pro-2@zazvick: ~/Projects/personal/training/bash-scripts (master)
$ usergreeting="$greeting, $USER"
Victors-MacBook-Pro-2@zazvick: ~/Projects/personal/training/bash-scripts (master)
$ echo $usergreeting
hello, zazvick
Victors-MacBook-Pro-2@zazvick: ~/Projects/personal/training/bash-scripts (master)
$ x = 5
-bash: x: command not found
Victors-MacBook-Pro-2@zazvick: ~/Projects/personal/training/bash-scripts (master)
$ x=5
Victors-MacBook-Pro-2@zazvick: ~/Projects/personal/training/bash-scripts (master)
$ $x
-bash: 5: command not found
Victors-MacBook-Pro-2@zazvick: ~/Projects/personal/training/bash-scripts (master)
$ echo $x
5
Victors-MacBook-Pro-2@zazvick: ~/Projects/personal/training/bash-scripts (master)

  • Used to store data by name

  • To create: just assign a value

    • x=10
    • If x already existed, it is assigned the new value
    • filenames="notes.txt picture.jpg movie.mov"
    • Values containing spaces: use quotes
    • Don't use white space around =

  • To get the value

    • Prefix with $
    • echo $x

  • Bash variables have no type

    • Basically just store a string

  • Names:

    • Only letters, numbers, and underscore are allowed
    • First character should be a letter or an underscore
    • Variable names are case-sensitive

  • Upercase variables:

  • Bash has many pre-defined variables
  • PATH, HOME, SECONDS, IFS, etc.
  • You don't want to override them by mistake
  • Good Habit:
  • Use lowercase names for your variables
  • Good habit: surround your variables with quotes
  • Use "$x" instead of $x
  • Prevent surprises when it contains spaces
  • User double quotes: keep meaning of dollar sign intact
  • Braces
  • Where does your variable name end?
  • echo "${foo}bar"
  • prints value of var "foo" followed by string "bar" echo "$foobar" prints value of "foobar"
  • Using braces a lot is a Good Habit
  • Another good habit
  • use $HOME instead of ~
  • read
  • Reads a line of input into variable
  • read var
  • Is a shell builtin
  • "help read"
  • "man builtins"
  • read -p "Type your name:" name
  • Debugging
  • user -x
  • set -x : set options to bash
  • set + x
  • Summary
  • Variables
    • Assign value
    • Get value ($)
    • No whitespace around=
  • Variables
    • Quotes
    • Braces
  • Reading input
    • read
  • Debugging
    • Use -x option in hashbang line
    • Or use "set-x" to enable and "set +x" to disable