This is a text-only version of the following page on https://raymii.org:

This is a text-only version of the following page on https://raymii.org:
---
Title : Bash Bits: Simple command line arguments
Author : Remy van Elst
Date : 30-12-2013
URL : https://raymii.org/s/snippets/Bash_Bits_Simple_Command_Line_Arguments.html
Format : Markdown/HTML
---

Bash Bits are small examples and tips for Bash Scripts. This bash bit shows you
how to add command line arguments to your script. It is very simple, non-
positional and does not use getopts.

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Sometimes a script need to have a variable which you don't know on forehand or
can change later. Or you have a script which works on a file, therefore you need
a filename. For example, when you have a script that adds a watermark to an
image. It is nice if you can give both the filename and the watermark as
parameters to the script.

Note that this is very very simple. The arguments must be given in order and it
does not support parameters like `--file/-f`. If you need something quick and
simple, this is very usable, if you need something more advanced it might be
better to take a look at `getopts` or `shift`.

The following example takes one required parameter, and one optional one. If the
first (filename) is not given, an error message plus usage is printed and the
script exits. A second parameter can be given but is optional. If that is not
given the script will use the default.

By using the `-z` option in the `if` statement, we check if the variable is
null, that is, has zero length.

if [[ -z "${1}" ]]; then
echo -e "[ERROR] Please give a filename to watermark and an optional watermark. Otherwise the default is used."
echo -e "${0} example.jpg"
exit 255

else
FILE="${1}"
fi

if [[ -z "${2}" ]]; then
WATERMARK="Picture Watermark"

else
WATERMARK="${2}"
fi

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[2]: https://raymii.org/s/tags/bash-bits.html

---

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