34 lines
6.6 KiB
Markdown
34 lines
6.6 KiB
Markdown
## Marking a script as executable
|
||
Sometimes, you may need to mark a script as an executable to run it. On Linux, this can be accomplished by `chmod +x [FILE]`, where `[FILE]` is the file you want to mark as executable. To unmark a file as executable, use `chmod -x`
|
||
|
||
## The Shebang
|
||
There are various shells with their own language syntax (`sh`, `bash`, `fish`, etc). Therefore, more complicated scripts will indicate a particular shell by specifying the absolute path to the interpreter as the first line, prefixed by `#!` like this:
|
||
```sh
|
||
#!/bin/sh
|
||
echo "Hello, World!"
|
||
```
|
||
`#!/bin/sh` means that this script can be executed by the binary located at `/bin/sh`, and so the reader knows this is a `sh`(ell) script.
|
||
|
||
## Variables
|
||
In bash, variable assignment is done with the `=` operator. Variables are conventionally named with `SCREAMING_SNAKE_CASE`, and can be accessed by prefixing the variable name with a dollar sign (`$`):
|
||
```bash
|
||
#!/bin/bash
|
||
# There may not be any spaces used during assignment, `A = B` means something different than `A=B`
|
||
# Assignment is done with the equal sign (=) operator:
|
||
MY_VARIABLE="Hi Mom!"
|
||
echo $MY_VARIABLE
|
||
```
|
||
|
||
## Quotes
|
||
In Bash, different styles of quotes mean different things:
|
||
|
||
| Quote | Description |
|
||
| ----------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
|
||
| Single Quotes (') | Enclosing characters in single quotes (`'`) preserves the literal value of each character within the quotes. A single quote may not occur between single quotes, even when preceded by a backslash. Commands in single quotes will not be evaluated. |
|
||
| Double Quotes (") | Enclosing characters in double quotes (`"`) preserves the literal value of all characters within the quotes, with the exception of `$`, \`, `\`, and, when history expansion is enabled, `!`. When the shell is in POSIX mode (see Bash POSIX Mode), the ‘!’ has no special meaning within double quotes, even when history expansion is enabled. The characters `$` and \‘ retain their special meaning within double quotes (see Shell Expansions). The backslash retains its special meaning only when followed by one of the following characters: `$`, ‘\`’, ‘"’, ‘\’, or newline. Within double quotes, backslashes that are followed by one of these characters are removed. Backslashes preceding characters without a special meaning are left unmodified. A double quote may be quoted within double quotes by preceding it with a backslash. If enabled, history expansion will be performed unless an ‘!’ appearing in double quotes is escaped using a backslash. The backslash preceding the ‘!’ is not removed. |
|
||
| | |
|
||
## Commands
|
||
| Command | Description |
|
||
| ------------- | ---------------------------------------------------------------------------------------------- |
|
||
| `exit [CODE]` | Make the script process exit, where `[CODE]` is the exit code the process will terminate with. |
|
||
| | | |