38 lines
4.9 KiB
Markdown
38 lines
4.9 KiB
Markdown
## Marking a script as executable
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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`
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## The Shebang
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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:
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```sh
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#!/bin/sh
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echo "Hello, World!"
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```
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`#!/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.
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## Variables
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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 (`$`):
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```bash
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#!/bin/bash
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# There may not be any spaces used during assignment, `A = B` means something different than `A=B`
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# Assignment is done with the equal sign (=) operator:
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MY_VARIABLE="Hi Mom!"
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echo $MY_VARIABLE
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```
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## Quotes
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In Bash, different styles of quotes (or a backtick) mean different things:
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| Quote | Description |
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| ----------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
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| Single Quotes (') | Enclosing characters in single quotes (`'`) preserves the literal value of each character within the quotes. A single quote may not occur between single quotes, even when preceded by a backslash. Commands in single quotes will not be evaluated. |
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| Double Quotes (") | Enclosing characters in double quotes (`"`) preserves the literal value of all characters within the quotes, with the exception of `$`, \`, `\`, and, when history expansion is enabled, `!`. The characters `$` and \‘ retain their special meaning within double quotes. A double quote may be quoted within double quotes by preceding it with a backslash. When the shell is in POSIX mode (see Bash POSIX Mode), the ‘!’ has no special meaning within double quotes, even when history expansion is enabled.<br><br>Within double quotes, substitution can be done using `$()`.<br><br>```<br>"Output of ls: $(ls)"<br>``` |
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| Backtick (\`) | While a backtick is not technically a quotation mark, it's included here. Backticks are used to substitute the output a command in a location:<br>```<br>sudo chown `id -u` /some/directory<br>``` |
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## Conditionals
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## Commands
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| Command | Description |
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| ----------------- | ---------------------------------------------------------------------------------------------- |
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| `exit [CODE]` | Make the script process exit, where `[CODE]` is the exit code the process will terminate with. |
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| `read [VARIABLE]` | Read user input into the provided variable. |
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