Bash: an introduction

So far you have typed commands one at a time. When a sequence of ten commands repeats every day, it is time to save it in a file. That file is a script, and Bash reads it the same way it reads the lines you type by hand.

A script is an ordinary text file. To tell the system which program runs it, the first line starts with a shebang:

#!/usr/bin/env bash
echo "hello from a script"

The line #!/usr/bin/env bash finds bash through PATH instead of hard-coding a path like /bin/bash. To run the file as a program, it needs the execute bit:

$ chmod +x hello.sh   # allow execution
$ ./hello.sh          # run it from the current directory

Variables and quoting

A variable hold