diff --git a/.gitignore b/.gitignore
index 02866f6..0049502 100644
--- a/.gitignore
+++ b/.gitignore
@@ -3,4 +3,7 @@
 *.iml
 
 # test data
-*.json
\ No newline at end of file
+*.json
+
+# local install script
+install.sh
\ No newline at end of file
diff --git a/Cargo.lock b/Cargo.lock
index a62a213..35e42b5 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1,5 +1,253 @@
 # This file is automatically @generated by Cargo.
 # It is not intended for manual editing.
+[[package]]
+name = "atty"
+version = "0.2.14"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d9b39be18770d11421cdb1b9947a45dd3f37e93092cbf377614828a319d5fee8"
+dependencies = [
+ "hermit-abi",
+ "libc",
+ "winapi",
+]
+
+[[package]]
+name = "autocfg"
+version = "1.0.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cdb031dd78e28731d87d56cc8ffef4a8f36ca26c38fe2de700543e627f8a464a"
+
+[[package]]
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+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cf1de2fe8c75bc145a2f577add951f8134889b4795d47466a54a5c846d691693"
+
+[[package]]
+name = "clap"
+version = "3.0.0-beta.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4bd1061998a501ee7d4b6d449020df3266ca3124b941ec56cf2005c3779ca142"
+dependencies = [
+ "atty",
+ "bitflags",
+ "clap_derive",
+ "indexmap",
+ "lazy_static",
+ "os_str_bytes",
+ "strsim",
+ "termcolor",
+ "textwrap",
+ "unicode-width",
+ "vec_map",
+]
+
+[[package]]
+name = "clap_derive"
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+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "370f715b81112975b1b69db93e0b56ea4cd4e5002ac43b2da8474106a54096a1"
+dependencies = [
+ "heck",
+ "proc-macro-error",
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
+[[package]]
+name = "hashbrown"
+version = "0.11.2"
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+checksum = "ab5ef0d4909ef3724cc8cce6ccc8572c5c817592e9285f5464f8e86f8bd3726e"
+
+[[package]]
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+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6d621efb26863f0e9924c6ac577e8275e5e6b77455db64ffa6c65c904e9e132c"
+dependencies = [
+ "unicode-segmentation",
+]
+
+[[package]]
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+checksum = "62b467343b94ba476dcb2500d242dadbb39557df889310ac77c5d99100aaac33"
+dependencies = [
+ "libc",
+]
+
+[[package]]
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+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bc633605454125dec4b66843673f01c7df2b89479b32e0ed634e43a91cff62a5"
+dependencies = [
+ "autocfg",
+ "hashbrown",
+]
+
 [[package]]
 name = "jsonformat"
 version = "0.1.0"
+dependencies = [
+ "clap",
+]
+
+[[package]]
+name = "lazy_static"
+version = "1.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e2abad23fbc42b3700f2f279844dc832adb2b2eb069b2df918f455c4e18cc646"
+
+[[package]]
+name = "libc"
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+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "320cfe77175da3a483efed4bc0adc1968ca050b098ce4f2f1c13a56626128790"
+
+[[package]]
+name = "os_str_bytes"
+version = "2.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "afb2e1c3ee07430c2cf76151675e583e0f19985fa6efae47d6848a3e2c824f85"
+
+[[package]]
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+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "da25490ff9892aab3fcf7c36f08cfb902dd3e71ca0f9f9517bea02a73a5ce38c"
+dependencies = [
+ "proc-macro-error-attr",
+ "proc-macro2",
+ "quote",
+ "syn",
+ "version_check",
+]
+
+[[package]]
+name = "proc-macro-error-attr"
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+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a1be40180e52ecc98ad80b184934baf3d0d29f979574e439af5a55274b35f869"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "version_check",
+]
+
+[[package]]
+name = "proc-macro2"
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+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f0d8caf72986c1a598726adc988bb5984792ef84f5ee5aa50209145ee8077038"
+dependencies = [
+ "unicode-xid",
+]
+
+[[package]]
+name = "quote"
+version = "1.0.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c3d0b9745dc2debf507c8422de05d7226cc1f0644216dfdfead988f9b1ab32a7"
+dependencies = [
+ "proc-macro2",
+]
+
+[[package]]
+name = "strsim"
+version = "0.10.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "73473c0e59e6d5812c5dfe2a064a6444949f089e20eec9a2e5506596494e4623"
+
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+ "proc-macro2",
+ "quote",
+ "unicode-xid",
+]
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+ "winapi-util",
+]
+
+[[package]]
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+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "203008d98caf094106cfaba70acfed15e18ed3ddb7d94e49baec153a2b462789"
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+ "unicode-width",
+]
+
+[[package]]
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+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8895849a949e7845e06bd6dc1aa51731a103c42707010a5b591c0038fb73385b"
+
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+
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+
+[[package]]
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+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f1bddf1187be692e79c5ffeab891132dfb0f236ed36a43c7ed39f1165ee20191"
+
+[[package]]
+name = "version_check"
+version = "0.9.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5fecdca9a5291cc2b8dcf7dc02453fee791a280f3743cb0905f8822ae463b3fe"
+
+[[package]]
+name = "winapi"
+version = "0.3.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5c839a674fcd7a98952e593242ea400abe93992746761e38641405d28b00f419"
+dependencies = [
+ "winapi-i686-pc-windows-gnu",
+ "winapi-x86_64-pc-windows-gnu",
+]
+
+[[package]]
+name = "winapi-i686-pc-windows-gnu"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ac3b87c63620426dd9b991e5ce0329eff545bccbbb34f3be09ff6fb6ab51b7b6"
+
+[[package]]
+name = "winapi-util"
+version = "0.1.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "70ec6ce85bb158151cae5e5c87f95a8e97d2c0c4b001223f33a334e3ce5de178"
+dependencies = [
+ "winapi",
+]
+
+[[package]]
+name = "winapi-x86_64-pc-windows-gnu"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "712e227841d057c1ee1cd2fb22fa7e5a5461ae8e48fa2ca79ec42cfc1931183f"
diff --git a/Cargo.toml b/Cargo.toml
index 155214b..35961f7 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -8,3 +8,4 @@ description = "Reads raw json from stdin and formats it to stdout"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
+clap = "3.0.0-beta.2"
\ No newline at end of file
diff --git a/src/lib.rs b/src/lib.rs
index 9f12788..614bd44 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,5 +1,14 @@
-pub fn format_json(json: &str, indent_str: &str) -> String {
-    let mut out = String::with_capacity(json.len()); // at least as big as the input
+///
+/// # Formats a json string
+///
+/// The indentation can be set to any custom value  
+/// The default value is two spaces
+/// The default indentation is faster than a custom one
+///
+pub fn format_json(json: &str, indentation: Option<&str>) -> String {
+    // at least as big as the input to avoid resizing
+    // this might be too big if the input string is formatted in a weird way, but that's not expected
+    let mut out = String::with_capacity(json.len());
 
     let mut escaped = false;
     let mut in_string = false;
@@ -42,9 +51,9 @@ pub fn format_json(json: &str, indent_str: &str) -> String {
                 '}' | ']' => {
                     indent_level -= 1;
                     if !newline_requested {
-                        // see comment above
+                        // see comment below about newline_requested
                         out.push('\n');
-                        indent(&mut out, indent_level, indent_str);
+                        indent(&mut out, indent_level, indentation);
                     }
                 }
                 ':' => {
@@ -59,8 +68,10 @@ pub fn format_json(json: &str, indent_str: &str) -> String {
             }
             if newline_requested && char != ']' && char != '}' {
                 // newline only happens after { [ and ,
+                // this means we can safely assume that it being followed up by } or ]
+                // means an empty object/array
                 out.push('\n');
-                indent(&mut out, old_level, indent_str);
+                indent(&mut out, old_level, indentation);
             }
 
             if auto_push {
@@ -74,76 +85,83 @@ pub fn format_json(json: &str, indent_str: &str) -> String {
     out
 }
 
-fn indent(buf: &mut String, level: usize, indent_str: &str) {
+fn indent(buf: &mut String, level: usize, indent_str: Option<&str>) {
     for _ in 0..level {
-        buf.push_str(indent_str);
+        match indent_str {
+            None => {
+                buf.push(' ');
+                buf.push(' ');
+            }
+            Some(indent) => {
+                buf.push_str(indent);
+            }
+        }
     }
 }
 
 #[cfg(test)]
 mod test {
-    const INDENT: &str = " ";
     use super::*;
 
     #[test]
     fn echoes_primitive() {
         let json = "1.35";
-        assert_eq!(json, format_json(json, INDENT));
+        assert_eq!(json, format_json(json, None));
     }
 
     #[test]
     fn ignore_whitespace_in_string() {
         let json = "\" hallo \"";
-        assert_eq!(json, format_json(json, INDENT));
+        assert_eq!(json, format_json(json, None));
     }
 
     #[test]
     fn remove_leading_whitespace() {
         let json = "   0";
         let expected = "0";
-        assert_eq!(expected, format_json(json, INDENT));
+        assert_eq!(expected, format_json(json, None));
     }
 
     #[test]
     fn handle_escaped_strings() {
         let json = "  \" hallo \\\" \" ";
         let expected = "\" hallo \\\" \"";
-        assert_eq!(expected, format_json(json, INDENT));
+        assert_eq!(expected, format_json(json, None));
     }
 
     #[test]
     fn simple_object() {
         let json = "{\"a\":0}";
         let expected = "{
- \"a\": 0
+  \"a\": 0
 }";
-        assert_eq!(expected, format_json(json, INDENT));
+        assert_eq!(expected, format_json(json, None));
     }
 
     #[test]
     fn simple_array() {
         let json = "[1,2,null]";
         let expected = "[
- 1,
- 2,
- null
+  1,
+  2,
+  null
 ]";
-        assert_eq!(expected, format_json(json, INDENT));
+        assert_eq!(expected, format_json(json, None));
     }
 
     #[test]
     fn array_of_object() {
         let json = "[{\"a\": 0}, {}, {\"a\": null}]";
         let expected = "[
- {
-  \"a\": 0
- },
- {},
- {
-  \"a\": null
- }
+  {
+    \"a\": 0
+  },
+  {},
+  {
+    \"a\": null
+  }
 ]";
 
-        assert_eq!(expected, format_json(json, INDENT));
+        assert_eq!(expected, format_json(json, None));
     }
 }
diff --git a/src/main.rs b/src/main.rs
index bbbf69b..d3ff159 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,12 +1,21 @@
+use clap::clap_app;
 use jsonformat::format_json;
 use std::fs;
 use std::io;
 use std::io::Read;
 
 fn main() -> Result<(), io::Error> {
-    let filename = std::env::args().skip(1).next();
+    let matches = clap_app!(jsonformat =>
+        (version: "1.0")
+        (author: "nilstrieb <nilstrieb@gmail.com>")
+        (about: "Formats json")
+        (@arg indentation: -i --indent +takes_value "Set the indentation used (\\s for space, \\t for tab)")
+        (@arg output: -o --output +takes_value "The output file for the formatted json")
+        (@arg input: "The input file to format")
+    )
+    .get_matches();
 
-    let str = match filename {
+    let str = match matches.value_of("input") {
         Some(path) => fs::read_to_string(path)?,
         None => {
             let mut buf = String::new();
@@ -16,7 +25,18 @@ fn main() -> Result<(), io::Error> {
         }
     };
 
-    println!("{}", format_json(&str, "  "));
+    let replaced_indent = matches
+        .value_of("indentation")
+        .map(|value| value.replace("s", " ").replace("t", "\t"));
+
+    let formatted = format_json(&str, replaced_indent.as_deref());
+
+    match matches.value_of("output") {
+        Some(file) => {
+            fs::write(file, formatted)?;
+        }
+        None => println!("{}", formatted),
+    }
 
     Ok(())
 }