34 lines
7.4 KiB
Markdown
34 lines
7.4 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 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, ‘!’. When the shell is in POSIX mode (see [Bash POSIX Mode](https://www.gnu.org/software/bash/manual/html_node/Bash-POSIX-Mode.html)), the ‘!’ has no special meaning within double quotes, even when history expansion is enabled. The characters ‘$’ and ‘`’ retain their special meaning within double quotes (see [Shell Expansions](https://www.gnu.org/software/bash/manual/html_node/Shell-Expansions.html)). The backslash retains its special meaning only when followed by one of the following characters: ‘$’, ‘`’, ‘"’, ‘\’, 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. |
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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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