Bash Script

Index

1. Sample Script clone branch to temp
2. Sample Script count files
3. Sample Script functions
4. Sample Script init js

Tips

Create and Run bash scripts

# For a new script, just alone this would fail with permission denied
$ ./script.sh

# Change permissions for user to be able to execute the file
$ chmod u+x script.sh

# Or change permissions for all user to be able to execute the file
$ chmod +x script.sh

# You can pass parameters to the script following $1, $2, $3, . . order in the script

Making a script executable

$ cp script.sh /usr/local/bin/<command>

Exit status in bash

In bash, every script, command or function that runs, returns an exit status.

Exit status can range from 0 to 255
Successful execution of a command will return 0

Example:
$ ls
$ echo $?
$ ls donotexist
$ echo $?

Syntax

Conditional Statements

if [[ -z myvar ]]; then              # Check is the variable is empty
    echo "true"
elif [[ -e script.sh ]]; then        # Check is file exists
    echo "true"
elif [[ 1 -eq 1 ]]; then             # Numeric equal check
    echo "true"
elif [[ $USER = 'anshul' ]]; then    # Any condition
    echo "true"
else
    echo "false"
fi

Ternary Operation
[[ $USER = 'anshul' ]] && echo "true" || echo "false"

Handling Variables

Setting and Unsetting an environment variable

Bash sets a lot of environment variables.
$ env           # list all the current environment variables
$ var=12        # Sets a variable (not an environment variable)
$ export var    # makes the variable visible to all child processes in context of current shell
$ unset var     # unsets the variable